Patent Publication Number: US-2010115667-A1

Title: Novel At1g67330 gene involved in altered nitrate uptake efficiency

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 of a provisional application Ser. No. 61/198,223 filed Nov. 4, 2008, which application is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of molecular biology. 
     BACKGROUND OF THE INVENTION 
     The domestication of many plants has correlated with dramatic increases in yield. Most phenotypic variation occurring in natural populations is continuous and is effected by multiple gene influences. The identification of specific genes responsible for the dramatic differences in yield, in domesticated plants, has become an important focus of agricultural research. 
     One group of genes effecting yield are the nitrogen utilization efficiency (NUE) genes. These genes have utility for improving the use of nitrogen in crop plants, especially maize. Increased nitrogen use efficiency can result from enhanced uptake and assimilation of nitrogen fertilizer and/or the subsequent remobilization and reutilization of accumulated nitrogen reserves. The genes can be used to alter the genetic composition of the plants rendering them more productive with current fertilizer application standards, or maintaining their productive rates with significantly reduced fertilizer input. Plants containing these genes can therefore be used for the enhancement of yield. Improving the NUE in corn would increase corn harvestable yield per unit of input nitrogen fertilizer, both in developing nations where access to nitrogen fertilizer is limited and in developed nations were the level of nitrogen use remains high. Nitrogen utilization improvement also allows decreases in on-farm input costs, decreased use and dependence on the non-renewable energy sources required for nitrogen fertilizer production, and decreases the environmental impact of nitrogen fertilizer manufacturing and agricultural use. 
     SUMMARY OF THE INVENTION 
     The present invention provides polynucleotides, related polypeptides and all conservatively modified variants of a novel gene, At1g67330 that has been shown to be involved in nitrogen uptake in plants. 
     The present invention presents methods to alter the genetic composition of crop plants, especially maize, so that such crops can be more productive with current fertilizer applications and/or as productive with significantly reduced fertilizer input. The utility of this class of invention is then both yield enhancement and reduced fertilizer costs with corresponding reduced impact to the environment. The genetic enhancement of the crop plant&#39;s intrinsic genetics in order to enhance NUE has not been achieved by scientists in the past in any commercially viable sense. This invention involves the discovery and characterization of a novel nitrogen uptake gene in plants. According to the invention, applicants have identified a gene, At1g67330, which has been shown to increase nitrate uptake efficiency by a pH indicator dye and nitrate uptake assays. The gene has been shown to increase fresh weight of plants at low nitrogen levels and to increase root and leaf mass in the presence of sucrose. Thus, the gene offers the ability to affect nitrogen uptake and concomitant nitrogen use efficiency. The gene encodes a protein which contains a predicted transmembrane domain, a putative nitrate-inducible sequence in the 5′UTR and 3′UTR (Rastogi et al. Plant Molecular Biology, Vol. 34(3), 465-476, June 1997) and is preferentially expressed in roots in the root hair zone, lateral root region, and elongation zone (Zimmermann et al. Plant Physiology, Vol. 136, 2621-2632, September 2004). 
     Therefore, in one aspect, the present invention relates to an isolated nucleic acid comprising an isolated polynucleotide sequence encoding a nitrate uptake associated gene. One embodiment of the invention is an isolated polynucleotide comprising a nucleotide sequence selected from the group consisting of: (a) the nucleotide sequence comprising SEQ ID NO: 1 (b) the nucleotide sequence encoding an amino acid sequence comprising SEQ ID NO: 2 and (c) the nucleotide sequence comprising at least 70% sequence identity to SEQ ID NO: 1, wherein said polynucleotide encodes a polypeptide affecting NUE activity. 
     Compositions of the invention include an isolated polypeptide comprising an amino acid sequence selected from the group consisting of: (a) the amino acid sequence comprising SEQ ID NO:2 and (b) the amino acid sequence comprising at least 70% sequence identity to SEQ ID NO:2 wherein said polypeptide has effects on NUE. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Polynucleotide/ 
                   
               
               
                 SE1Q ID NO: 
                 polypeptide 
                 Identity 
               
               
                   
               
             
            
               
                 SEQ ID NO: 1 
                 polynucleotide 
                 At1g67330 
               
               
                 SEQ ID NO: 2 
                 polypeptide 
                 At1g67330 
               
               
                 SEQ ID NO: 3 
                 polypeptide 
                 Dicot_At_At1g27930.1 
               
               
                 SEQ ID NO: 4 
                 polypeptide 
                 Dicot_Bs_PBR110841 
               
               
                 SEQ ID NO: 5 
                 polypeptide 
                 Dicot_Bs_PBR117871 
               
               
                 SEQ ID NO: 6 
                 polypeptide 
                 Monocot_Os_Os11g29780.1 
               
               
                 SEQ ID NO: 7 
                 polypeptide 
                 Monocot_Sb_Sb05g106480 
               
               
                 SEQ ID NO: 8 
                 polypeptide 
                 Monocot_Zm_pco639489 
               
               
                 SEQ ID NO: 9 
                 polypeptide 
                 Dicot_Mt_CT737180 
               
               
                 SEQ ID NO: 10 
                 polypeptide 
                 Dicot_Pt_548026 
               
               
                 SEQ ID NO: 11 
                 polypeptide 
                 Dicot_Pt_554785 
               
               
                 SEQ ID NO: 12 
                 polypeptide 
                 Dicot_Vv_CAN63149. 
               
               
                 SEQ ID NO: 13 
                 polypeptide 
                 Dicot_Vv_CAO66163.1 
               
               
                 SEQ ID NO: 14 
                 polypeptide 
                 Dicot_Vv_CAO49019.1 
               
               
                 SEQ ID NO: 15 
                 polypeptide 
                 Consensus sequence 
               
               
                 SEQ ID NO: 16 
                 polynucleotide 
                 Monocot_Zm_pco639489 
               
               
                   
               
            
           
         
       
     
     In another aspect, the present invention relates to a recombinant expression cassette comprising a nucleic acid as described. Additionally, the present invention relates to a vector containing the recombinant expression cassette. Further, the vector containing the recombinant expression cassette can facilitate the transcription and translation of the nucleic acid in a host cell. The present invention also relates to the host cells able to express the polynucleotide of the present invention. A number of host cells could be used, such as but not limited to, microbial, mammalian, plant, or insect. 
     In yet another embodiment, the present invention is directed to a transgenic plant or plant cells, containing the nucleic acids of the present invention. Preferred plants containing the polynucleotides of the present invention include but are not limited to maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, tomato, and millet. In another embodiment, the transgenic plant is a maize plant or plant cells. Another embodiment is the transgenic seeds from the transgenic nitrate uptake-associated polypeptide of the invention operably linked to a promoter that drives expression in the plant. The plants of the invention can have altered NUE as compared to a control plant. In some plants, the NUE is altered in a vegetative tissue, a reproductive tissue, or a vegetative tissue and a reproductive tissue. Plants of the invention can have at least one of the following phenotypes including but not limited to: increased root mass, increased root length, increased leaf size, increased ear size, increased seed size, increased green color, increased endosperm size, alterations in the relative size of embryos and endosperms leading to changes in the relative levels of protein, oil, and/or starch in the seeds, absence of tassels, absence of functional pollen bearing tassels, or increased plant size. 
     Another embodiment of the invention would be plants that have been genetically modified at a genomic locus, wherein the genomic locus encodes a nitrate uptake-associated polypeptide of the invention. 
     Methods for increasing the activity of a nitrate uptake-associated polypeptide in a plant are provided. The method can comprise introducing into the plant a nitrate uptake-associated polynucleotide of the invention. 
     Methods for reducing or eliminating the level of a nitrate uptake-associated polypeptide in the plant are provided. The level or activity of the polypeptide could also be reduced or eliminated in specific tissues, causing alteration in plant growth rate. Reducing the level and/or activity of the nitrate uptake-associated polypeptide may lead to smaller stature or slower growth of plants. 
    
    
     
       DETAILED DESCRIPTION OF THE FIGURES 
       The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the United States Patent and Trademark Office upon request and payment of the necessary fee. 
         FIG. 1  depicts a Clustal W dendrogram alignment of 10 full length relatives to At1g67330 (SEQ ID NO: 2). The Rice Os11g29780.1,  Sorghum  Sb05g106480 and Maize PCO639489 appear to be a monocot ortholog grouping, likely representing a single gene from each species. 
         FIGS. 2A and 2B  show a sequence Clustal W alignment of a group of At1g67330 orthologs. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Unless mentioned otherwise, the techniques employed or contemplated herein are standard methodologies well known to one of ordinary skill in the art. The materials, methods and examples are illustrative only and not limiting. The following is presented by way of illustration and is not intended to limit the scope of the invention. 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 
     The practice of the present invention will employ, unless otherwise indicated, conventional techniques of botany, microbiology, tissue culture, molecular biology, chemistry, biochemistry and recombinant DNA technology, which are within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Langenheim and Thimann, (1982)  Botany: Plant Biology and Its Relation to Human Affairs , John Wiley;  Cell Culture and Somatic Cell Genetics of Plants , vol. 1, Vasil, ed. (1984); Stanier, et al., (1986)  The Microbial World,  5 th  ed., Prentice-Hall; Dhringra and Sinclair, (1985)  Basic Plant Pathology Methods , CRC Press; Maniatis, et al., (1982)  Molecular Cloning: A Laboratory Manual; DNA Cloning , vols. I and II, Glover, ed. (1985);  Oligonucleotide Synthesis , Gait, ed. (1984);  Nucleic Acid Hybridization , Hames and Higgins, eds. (1984); and the series  Methods in Enzymology , Colowick and Kaplan, eds, Academic Press, Inc., San Diego, Calif. 
     Units, prefixes, and symbols may be denoted in their SI accepted form. Unless otherwise indicated, nucleic acids are written left to right in 5′ to 3′ orientation; amino acid sequences are written left to right in amino to carboxy orientation, respectively. Numeric ranges are inclusive of the numbers defining the range. Amino acids may be referred to herein by either their commonly known three letter symbols or by the one-letter symbols recommended by the IUPAC-IUB Biochemical Nomenclature Commission. Nucleotides, likewise, may be referred to by their commonly accepted single-letter codes. The terms defined below are more fully defined by reference to the specification as a whole. 
     In describing the present invention, the following terms will be employed, and are intended to be defined as indicated below. 
     By “microbe” is meant any microorganism (including both eukaryotic and prokaryotic microorganisms), such as fungi, yeast, bacteria, actinomycetes, algae and protozoa, as well as other unicellular structures. 
     By “amplified” is meant the construction of multiple copies of a nucleic acid sequence or multiple copies complementary to the nucleic acid sequence using at least one of the nucleic acid sequences as a template. Amplification systems include the polymerase chain reaction (PCR) system, ligase chain reaction (LCR) system, nucleic acid sequence based amplification (NASBA, Cangene, Mississauga, Ontario), Q-Beta Replicase systems, transcription-based amplification system (TAS), and strand displacement amplification (SDA). See, e.g.,  Diagnostic Molecular Microbiology Principles and Applications , Persing, et al., eds., American Society for Microbiology, Washington, D.C. (1993). The product of amplification is termed an amplicon. 
     The term “conservatively modified variants” applies to both amino acid and nucleic acid sequences. With respect to particular nucleic acid sequences, conservatively modified variants refer to those nucleic acids that encode identical or conservatively modified variants of the amino acid sequences. Because of the degeneracy of the genetic code, a large number of functionally identical nucleic acids encode any given protein. For instance, the codons GCA, GCC, GCG and GCU all encode the amino acid alanine. Thus, at every position where an alanine is specified by a codon, the codon can be altered to any of the corresponding codons described without altering the encoded polypeptide. Such nucleic acid variations are “silent variations” and represent one species of conservatively modified variation. Every nucleic acid sequence herein that encodes a polypeptide also describes every possible silent variation of the nucleic acid. One of ordinary skill will recognize that each codon in a nucleic acid (except AUG, which is ordinarily the only codon for methionine; one exception is  Micrococcus rubens , for which GTG is the methionine codon (Ishizuka, et al., (1993)  J. Gen. Microbiol.  139:425-32) can be modified to yield a functionally identical molecule. Accordingly, each silent variation of a nucleic acid, which encodes a polypeptide of the present invention, is implicit in each described polypeptide sequence and incorporated herein by reference. 
     As to amino acid sequences, one of skill will recognize that individual substitutions, deletions or additions to a nucleic acid, peptide, polypeptide, or protein sequence which alters, adds or deletes a single amino acid or a small percentage of amino acids in the encoded sequence is a “conservatively modified variant” when the alteration results in the substitution of an amino acid with a chemically similar amino acid. Thus, any number of amino acid residues selected from the group of integers consisting of from 1 to 15 can be so altered. Thus, for example, 1, 2, 3, 4, 5, 7 or 10 alterations can be made. Conservatively modified variants typically provide similar biological activity as the unmodified polypeptide sequence from which they are derived. For example, substrate specificity, enzyme activity, or ligand/receptor binding is generally at least 30%, 40%, 50%, 60%, 70%, 80% or 90%, preferably 60-90% of the native protein for it&#39;s native substrate. Conservative substitution tables providing functionally similar amino acids are well known in the art. 
     The following six groups each contain amino acids that are conservative substitutions for one another: 
     1) Alanine (A), Serine (S), Threonine (T); 
     2) Aspartic acid (D), Glutamic acid (E); 
     3) Asparagine (N), Glutamine (Q); 
     4) Arginine (R), Lysine (K); 
     5) Isoleucine (I), Leucine (L), Methionine (M), Valine (V); and 
     6) Phenylalanine (F), Tyrosine (Y), Tryptophan (W). 
     See also, Creighton,  Proteins , W.H. Freeman and Co. (1984). 
     As used herein, “consisting essentially of” means the inclusion of additional sequences to an object polynucleotide where the additional sequences do not selectively hybridize, under stringent hybridization conditions, to the same cDNA as the polynucleotide and where the hybridization conditions include a wash step in 0.1×SSC and 0.1% sodium dodecyl sulfate at 65° C. 
     By “encoding” or “encoded,” with respect to a specified nucleic acid, is meant comprising the information for translation into the specified protein. A nucleic acid encoding a protein may comprise non-translated sequences (e.g., introns) within translated regions of the nucleic acid, or may lack such intervening non-translated sequences (e.g., as in cDNA). The information by which a protein is encoded is specified by the use of codons. Typically, the amino acid sequence is encoded by the nucleic acid using the “universal” genetic code. However, variants of the universal code, such as is present in some plant, animal, and fungal mitochondria, the bacterium  Mycoplasma capricolumn  (Yamao, et al., (1985)  Proc. Natl. Acad. Sci. USA  82:2306-9), or the ciliate Macronucleus, may be used when the nucleic acid is expressed using these organisms. 
     When the nucleic acid is prepared or altered synthetically, advantage can be taken of known codon preferences of the intended host where the nucleic acid is to be expressed. For example, although nucleic acid sequences of the present invention may be expressed in both monocotyledonous and dicotyledonous plant species, sequences can be modified to account for the specific codon preferences and GC content preferences of monocotyledonous plants or dicotyledonous plants as these preferences have been shown to differ (Murray, et al., (1989)  Nucleic Acids Res.  17:477-98 and herein incorporated by reference). Thus, the maize preferred codon for a particular amino acid might be derived from known gene sequences from maize. Maize codon usage for 28 genes from maize plants is listed in Table 4 of Murray, et al., supra. 
     As used herein, “heterologous” in reference to a nucleic acid is a nucleic acid that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous structural gene is from a species different from that from which the structural gene was derived or, if from the same species, one or both are substantially modified from their original form. A heterologous protein may originate from a foreign species or, if from the same species, is substantially modified from its original form by deliberate human intervention. 
     By “host cell” is meant a cell, which comprises a heterologous nucleic acid sequence of the invention, which contains a vector and supports the replication and/or expression of the expression vector. Host cells may be prokaryotic cells such as  E. coli , or eukaryotic cells such as yeast, insect, plant, amphibian, or mammalian cells. Preferably, host cells are monocotyledonous or dicotyledonous plant cells, including but not limited to maize, sorghum, sunflower, soybean, wheat, alfalfa, rice, cotton, canola, barley, millet, and tomato. A particularly preferred monocotyledonous host cell is a maize host cell. 
     The term “hybridization complex” includes reference to a duplex nucleic acid structure formed by two single-stranded nucleic acid sequences selectively hybridized with each other. 
     The term “introduced” in the context of inserting a nucleic acid into a cell, means “transfection” or “transformation” or “transduction” and includes reference to the incorporation of a nucleic acid into a eukaryotic or prokaryotic cell where the nucleic acid may be incorporated into the genome of the cell (e.g., chromosome, plasmid, plastid or mitochondrial DNA), converted into an autonomous replicon, or transiently expressed (e.g., transfected mRNA). 
     The terms “isolated” refers to material, such as a nucleic acid or a protein, which is substantially or essentially free from components which normally accompany or interact with it as found in its naturally occurring environment. The isolated material optionally comprises material not found with the material in its natural environment. Nucleic acids, which are “isolated”, as defined herein, are also referred to as “heterologous” nucleic acids. Unless otherwise stated, the term “nitrate uptake-associated nucleic acid” means a nucleic acid comprising a polynucleotide (“nitrate uptake-associated polynucleotide”) encoding a full length or partial length nitrate uptake-associated polypeptide. 
     As used herein, “nucleic acid” includes reference to a deoxyribonucleotide or ribonucleotide polymer in either single- or double-stranded form, and unless otherwise limited, encompasses known analogues having the essential nature of natural nucleotides in that they hybridize to single-stranded nucleic acids in a manner similar to naturally occurring nucleotides (e.g., peptide nucleic acids). 
     By “nucleic acid library” is meant a collection of isolated DNA or RNA molecules, which comprise and substantially represent the entire transcribed fraction of a genome of a specified organism. Construction of exemplary nucleic acid libraries, such as genomic and cDNA libraries, is taught in standard molecular biology references such as Berger and Kimmel, (1987)  Guide To Molecular Cloning Techniques , from the series  Methods in Enzymology , vol. 152, Academic Press, Inc., San Diego, Calif.; Sambrook, et al., (1989)  Molecular Cloning: A Laboratory Manual,  2 nd  ed., vols. 1-3; and  Current Protocols in Molecular Biology , Ausubel, et al., eds, Current Protocols, a joint venture between Greene Publishing Associates, Inc. and John Wiley &amp; Sons, Inc. (1994 Supplement). 
     As used herein “operably linked” includes reference to a functional linkage between a first sequence, such as a promoter, and a second sequence, wherein the promoter sequence initiates and mediates transcription of the DNA corresponding to the second sequence. Generally, operably linked means that the nucleic acid sequences being linked are contiguous and, where necessary to join two protein coding regions, contiguous and in the same reading frame. 
     As used herein, the term “plant” includes reference to whole plants, plant organs (e.g., leaves, stems, roots, etc.), seeds and plant cells and progeny of same. Plant cell, as used herein includes, without limitation, seeds, suspension cultures, embryos, meristematic regions, callus tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspores. The class of plants, which can be used in the methods of the invention, is generally as broad as the class of higher plants amenable to transformation techniques, including both monocotyledonous and dicotyledonous plants including species from the genera:  Cucurbita, Rosa, Vitis, Juglans, Fragaria, Lotus, Medicago, Onobrychis, Trifolium, Trigonella, Vigna, Citrus, Linum, Geranium, Manihot, Daucus, Arabidopsis, Brassica, Raphanus, Sinapis, Atropa, Capsicum, Datura, Hyoscyamus, Lycopersicon, Nicotiana, Solanum, Petunia, Digitalis, Majorana, Ciahorium, Helianthus, Lactuca, Bromus, Asparagus, Antirrhinum, Heterocallis, Nemesis, Pelargonium, Panieum, Pennisetum, Ranunculus, Senecio, Salpiglossis, Cucumis, Browaalia, Glycine, Pisum, Phaseolus, Lolium, Oryza, Avena, Hordeum, Secale, Allium , and  Triticum . A particularly preferred plant is  Zea mays.    
     As used herein, “yield” may include reference to bushels per acre of a grain crop at harvest, as adjusted for grain moisture (15% typically for maize, for example), and the volume of biomass generated (for forage crops such as alfalfa, and plant root size for multiple crops). Grain moisture is measured in the grain at harvest. The adjusted test weight of grain is determined to be the weight in pounds per bushel, adjusted for grain moisture level at harvest. Biomass is measured as the weight of harvestable plant material generated. 
     As used herein, “polynucleotide” includes reference to a deoxyribopolynucleotide, ribopolynucleotide, or analogs thereof that have the essential nature of a natural ribonucleotide in that they hybridize, under stringent hybridization conditions, to substantially the same nucleotide sequence as naturally occurring nucleotides and/or allow translation into the same amino acid(s) as the naturally occurring nucleotide(s). A polynucleotide can be full-length or a subsequence of a native or heterologous structural or regulatory gene. Unless otherwise indicated, the term includes reference to the specified sequence as well as the complementary sequence thereof. Thus, DNAs or RNAs with backbones modified for stability or for other reasons are “polynucleotides” as that term is intended herein. Moreover, DNAs or RNAs comprising unusual bases, such as inosine, or modified bases, such as tritylated bases, to name just two examples, are polynucleotides as the term is used herein. It will be appreciated that a great variety of modifications have been made to DNA and RNA that serve many useful purposes known to those of skill in the art. The term polynucleotide as it is employed herein embraces such chemically, enzymatically or metabolically modified forms of polynucleotides, as well as the chemical forms of DNA and RNA characteristic of viruses and cells, including inter alia, simple and complex cells. 
     The terms “polypeptide,” “peptide,” and “protein” are used interchangeably herein to refer to a polymer of amino acid residues. The terms apply to amino acid polymers in which one or more amino acid residue is an artificial chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally occurring amino acid polymers. 
     As used herein “promoter” includes reference to a region of DNA upstream from the start of transcription and involved in recognition and binding of RNA polymerase and other proteins to initiate transcription. A “plant promoter” is a promoter capable of initiating transcription in plant cells. Exemplary plant promoters include, but are not limited to, those that are obtained from plants, plant viruses, and bacteria which comprise genes expressed in plant cells such  Agrobacterium  or  Rhizobium . Examples are promoters that preferentially initiate transcription in certain tissues, such as leaves, roots, seeds, fibres, xylem vessels, tracheids, or sclerenchyma. Such promoters are referred to as “tissue preferred.” A “cell type” specific promoter primarily drives expression in certain cell types in one or more organs, for example, vascular cells in roots or leaves. An “inducible” or “regulatable” promoter is a promoter, which is under environmental control. Examples of environmental conditions that may effect transcription by inducible promoters include anaerobic conditions or the presence of light. Another type of promoter is a developmentally regulated promoter, for example, a promoter that drives expression during pollen development. Tissue preferred, cell type specific, developmentally regulated, and inducible promoters constitute the class of “non-constitutive” promoters. A “constitutive” promoter is a promoter, which is active under most environmental conditions. 
     The term “nitrate uptake-associated polypeptide” refers to one or more amino acid sequences. The term is also inclusive of fragments, variants, homologs, alleles or precursors (e.g., preproproteins or proproteins) thereof. A “nitrate uptake-associated protein” comprises a nitrate uptake-associated polypeptide. Unless otherwise stated, the term “nitrate uptake-associated nucleic acid” means a nucleic acid comprising a polynucleotide (“nitrate uptake-associated polynucleotide”) encoding a nitrate uptake-associated polypeptide. 
     As used herein “recombinant” includes reference to a cell or vector, that has been modified by the introduction of a heterologous nucleic acid or that the cell is derived from a cell so modified. Thus, for example, recombinant cells express genes that are not found in identical form within the native (non-recombinant) form of the cell or express native genes that are otherwise abnormally expressed, under expressed or not expressed at all as a result of deliberate human intervention; or may have reduced or eliminated expression of a native gene. The term “recombinant” as used herein does not encompass the alteration of the cell or vector by naturally occurring events (e.g., spontaneous mutation, natural transformation/transduction/transposition) such as those occurring without deliberate human intervention. 
     As used herein, a “recombinant expression cassette” is a nucleic acid construct, generated recombinantly or synthetically, with a series of specified nucleic acid elements, which permit transcription of a particular nucleic acid in a target cell. The recombinant expression cassette can be incorporated into a plasmid, chromosome, mitochondrial DNA, plastid DNA, virus, or nucleic acid fragment. Typically, the recombinant expression cassette portion of an expression vector includes, among other sequences, a nucleic acid to be transcribed, and a promoter. 
     The terms “residue” or “amino acid residue” or “amino acid” are used interchangeably herein to refer to an amino acid that is incorporated into a protein, polypeptide, or peptide (collectively “protein”). The amino acid may be a naturally occurring amino acid and, unless otherwise limited, may encompass known analogs of natural amino acids that can function in a similar manner as naturally occurring amino acids. 
     The term “selectively hybridizes” includes reference to hybridization, under stringent hybridization conditions, of a nucleic acid sequence to a specified nucleic acid target sequence to a detectably greater degree (e.g., at least 2-fold over background) than its hybridization to non-target nucleic acid sequences and to the substantial exclusion of non-target nucleic acids. Selectively hybridizing sequences typically have about at least 40% sequence identity, preferably 60-90% sequence identity, and most preferably 100% sequence identity (i.e., complementary) with each other. 
     The terms “stringent conditions” or “stringent hybridization conditions” include reference to conditions under which a probe will hybridize to its target sequence, to a detectably greater degree than other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. By controlling the stringency of the hybridization and/or washing conditions, target sequences can be identified which can be up to 100% complementary to the probe (homologous probing). Alternatively, stringency conditions can be adjusted to allow some mismatching in sequences so that lower degrees of similarity are detected (heterologous probing). Optimally, the probe is approximately 500 nucleotides in length, but can vary greatly in length from less than 500 nucleotides to equal to the entire length of the target sequence. 
     Typically, stringent conditions will be those in which the salt concentration is less than about 1.5 M Na ion, typically about 0.01 to 1.0 M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30° C. for short probes (e.g., 10 to 50 nucleotides) and at least about 60° C. for long probes (e.g., greater than 50 nucleotides). Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide or Denhardt&#39;s. Exemplary low stringency conditions include hybridization with a buffer solution of 30 to 35% formamide, 1 M NaCl, 1% SDS (sodium dodecyl sulphate) at 37° C., and a wash in 1× to 2×SSC (20×SSC=3.0 M NaCl/0.3 M trisodium citrate) at 50 to 55° C. Exemplary moderate stringency conditions include hybridization in 40 to 45% formamide, 1 M NaCl, 1% SDS at 37° C., and a wash in 0.5× to 1×SSC at 55 to 60° C. Exemplary high stringency conditions include hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37° C., and a wash in 0.1×SSC at 60 to 65° C. Specificity is typically the function of post-hybridization washes, the critical factors being the ionic strength and temperature of the final wash solution. For DNA-DNA hybrids, the T m  can be approximated from the equation of Meinkoth and Wahl, (1984)  Anal. Biochem.,  138:267-84: T m =81.5° C.+16.6 (log M)+0.41 (% GC)−0.61 (% form)−500/L; where M is the molarity of monovalent cations, % GC is the percentage of guanosine and cytosine nucleotides in the DNA, % form is the percentage of formamide in the hybridization solution, and L is the length of the hybrid in base pairs. The T m  is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. T m  is reduced by about 1° C. for each 1% of mismatching; thus, T m , hybridization and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, if sequences with ≧90% identity are sought, the T m  can be decreased 10° C. Generally, stringent conditions are selected to be about 5° C. lower than the thermal melting point (T m ) for the specific sequence and its complement at a defined ionic strength and pH. However, severely stringent conditions can utilize a hybridization and/or wash at 1, 2, 3 or 4° C. lower than the thermal melting point (T m ); moderately stringent conditions can utilize a hybridization and/or wash at 6, 7, 8, 9 or 10° C. lower than the thermal melting point (T m ); low stringency conditions can utilize a hybridization and/or wash at 11, 12, 13, 14, 15 or 20° C. lower than the thermal melting point (T m ). Using the equation, hybridization and wash compositions, and desired T m , those of ordinary skill will understand that variations in the stringency of hybridization and/or wash solutions are inherently described. If the desired degree of mismatching results in a T m  of less than 45° C. (aqueous solution) or 32° C. (formamide solution) it is preferred to increase the SSC concentration so that a higher temperature can be used. An extensive guide to the hybridization of nucleic acids is found in Tijssen,  Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes , part I, chapter 2, “Overview of principles of hybridization and the strategy of nucleic acid probe assays,” Elsevier, New York (1993); and  Current Protocols in Molecular Biology , chapter 2, Ausubel, et al., eds, Greene Publishing and Wiley-Interscience, New York (1995). Unless otherwise stated, in the present application high stringency is defined as hybridization in 4×SSC, 5×Denhardt&#39;s (5 g Ficoll, 5 g polyvinypyrrolidone, 5 g bovine serum albumin in 500 ml of water), 0.1 mg/ml boiled salmon sperm DNA, and 25 mM Na phosphate at 65° C., and a wash in 0.1×SSC, 0.1% SDS at 65° C. 
     As used herein, “transgenic plant” includes reference to a plant, which comprises within its genome a heterologous polynucleotide. Generally, the heterologous polynucleotide is stably integrated within the genome such that the polynucleotide is passed on to successive generations. The heterologous polynucleotide may be integrated into the genome alone or as part of a recombinant expression cassette. “Transgenic” is used herein to include any cell, cell line, callus, tissue, plant part or plant, the genotype of which has been altered by the presence of heterologous nucleic acid including those transgenics initially so altered as well as those created by sexual crosses or asexual propagation from the initial transgenic. The term “transgenic” as used herein does not encompass the alteration of the genome (chromosomal or extra-chromosomal) by conventional plant breeding methods or by naturally occurring events such as random cross-fertilization, non-recombinant viral infection, non-recombinant bacterial transformation, non-recombinant transposition, or spontaneous mutation. 
     As used herein, “vector” includes reference to a nucleic acid used in transfection of a host cell and into which can be inserted a polynucleotide. Vectors are often replicons. Expression vectors permit transcription of a nucleic acid inserted therein. 
     The following terms are used to describe the sequence relationships between two or more nucleic acids or polynucleotides or polypeptides: (a) “reference sequence,” (b) “comparison window,” (c) “sequence identity,” (d) “percentage of sequence identity,” and (e) “substantial identity.” 
     As used herein, “reference sequence” is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset or the entirety of a specified sequence; for example, as a segment of a full-length cDNA or gene sequence, or the complete cDNA or gene sequence. 
     As used herein, “comparison window” means includes reference to a contiguous and specified segment of a polynucleotide sequence, wherein the polynucleotide sequence may be compared to a reference sequence and wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. Generally, the comparison window is at least 20 contiguous nucleotides in length, and optionally can be 30, 40, 50, 100 or longer. Those of skill in the art understand that to avoid a high similarity to a reference sequence due to inclusion of gaps in the polynucleotide sequence a gap penalty is typically introduced and is subtracted from the number of matches. 
     Methods of alignment of nucleotide and amino acid sequences for comparison are well known in the art. The local homology algorithm (BESTFIT) of Smith and Waterman, (1981)  Adv. Appl. Math  2:482, may conduct optimal alignment of sequences for comparison; by the homology alignment algorithm (GAP) of Needleman and Wunsch, (1970)  J. Mol. Biol.  48:443-53; by the search for similarity method (Tfasta and Fasta) of Pearson and Lipman, (1988)  Proc. Natl. Acad. Sci. USA  85:2444; by computerized implementations of these algorithms, including, but not limited to: CLUSTAL in the PC/Gene program by Intelligenetics, Mountain View, Calif., GAP, BESTFIT, BLAST, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Version 8 (available from Genetics Computer Group (GCG® programs (Accelrys, Inc., San Diego, Calif.).). The CLUSTAL program is well described by Higgins and Sharp, (1988)  Gene  73:237-44; Higgins and Sharp, (1989)  CABIOS  5:151-3; Corpet, et al., (1988)  Nucleic Acids Res.  16:10881-90; Huang, et al., (1992)  Computer Applications in the Biosciences  8:155-65, and Pearson, et al., (1994)  Meth. Mol. Biol.  24:307-31. The preferred program to use for optimal global alignment of multiple sequences is PileUp (Feng and Doolittle, (1987)  J. Mol. Evol.,  25:351-60 which is similar to the method described by Higgins and Sharp, (1989)  CABIOS  5:151-53 and hereby incorporated by reference). The BLAST family of programs which can be used for database similarity searches includes: BLASTN for nucleotide query sequences against nucleotide database sequences; BLASTX for nucleotide query sequences against protein database sequences; BLASTP for protein query sequences against protein database sequences; TBLASTN for protein query sequences against nucleotide database sequences; and TBLASTX for nucleotide query sequences against nucleotide database sequences. See,  Current Protocols in Molecular Biology , Chapter 19, Ausubel et al., eds., Greene Publishing and Wiley-Interscience, New York (1995). 
     GAP uses the algorithm of Needleman and Wunsch, supra, to find the alignment of two complete sequences that maximizes the number of matches and minimizes the number of gaps. GAP considers all possible alignments and gap positions and creates the alignment with the largest number of matched bases and the fewest gaps. It allows for the provision of a gap creation penalty and a gap extension penalty in units of matched bases. GAP must make a profit of gap creation penalty number of matches for each gap it inserts. If a gap extension penalty greater than zero is chosen, GAP must, in addition, make a profit for each gap inserted of the length of the gap times the gap extension penalty. Default gap creation penalty values and gap extension penalty values in Version 10 of the Wisconsin Genetics Software Package are 8 and 2, respectively. The gap creation and gap extension penalties can be expressed as an integer selected from the group of integers consisting of from 0 to 100. Thus, for example, the gap creation and gap extension penalties can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50 or greater. 
     GAP presents one member of the family of best alignments. There may be many members of this family, but no other member has a better quality. GAP displays four figures of merit for alignments: Quality, Ratio, Identity, and Similarity. The Quality is the metric maximized in order to align the sequences. Ratio is the quality divided by the number of bases in the shorter segment. Percent Identity is the percent of the symbols that actually match. Percent Similarity is the percent of the symbols that are similar. Symbols that are across from gaps are ignored. A similarity is scored when the scoring matrix value for a pair of symbols is greater than or equal to 0.50, the similarity threshold. The scoring matrix used in Version 10 of the Wisconsin Genetics Software Package is BLOSUM62 (see, Henikoff and Henikoff, (1989)  Proc. Natl. Acad. Sci. USA  89:10915). 
     Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using the BLAST 2.0 suite of programs using default parameters (Altschul, et al., (1997)  Nucleic Acids Res.  25:3389-402). 
     As those of ordinary skill in the art will understand, BLAST searches assume that proteins can be modeled as random sequences. However, many real proteins comprise regions of nonrandom sequences, which may be homopolymeric tracts, short-period repeats, or regions enriched in one or more amino acids. Such low-complexity regions may be aligned between unrelated proteins even though other regions of the protein are entirely dissimilar. A number of low-complexity filter programs can be employed to reduce such low-complexity alignments. For example, the SEG (Wooten and Federhen, (1993)  Comput. Chem.  17:149-63) and XNU (Claverie and States, (1993)  Comput. Chem.  17:191-201) low-complexity filters can be employed alone or in combination. 
     As used herein, “sequence identity” or “identity” in the context of two nucleic acid or polypeptide sequences includes reference to the residues in the two sequences, which are the same when aligned for maximum correspondence over a specified comparison window. When percentage of sequence identity is used in reference to proteins it is recognized that residue positions which are not identical often differ by conservative amino acid substitutions, where amino acid residues are substituted for other amino acid residues with similar chemical properties (e.g., charge or hydrophobicity) and therefore do not change the functional properties of the molecule. Where sequences differ in conservative substitutions, the percent sequence identity may be adjusted upwards to correct for the conservative nature of the substitution. Sequences, which differ by such conservative substitutions, are said to have “sequence similarity” or “similarity.” Means for making this adjustment are well known to those of skill in the art. Typically this involves scoring a conservative substitution as a partial rather than a full mismatch, thereby increasing the percentage sequence identity. Thus, for example, where an identical amino acid is given a score of 1 and a non-conservative substitution is given a score of zero, a conservative substitution is given a score between zero and 1. The scoring of conservative substitutions is calculated, e.g., according to the algorithm of Meyers and Miller, (1988)  Computer Applic. Biol. Sci.  4:11-17, e.g., as implemented in the program PC/GENE (Intelligenetics, Mountain View, Calif., USA). 
     As used herein, “percentage of sequence identity” means the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity. 
     The term “substantial identity” of polynucleotide sequences means that a polynucleotide comprises a sequence that has between 50-100% sequence identity, preferably at least 50% sequence identity, preferably at least 60% sequence identity, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and most preferably at least 95%, compared to a reference sequence using one of the alignment programs described using standard parameters. One of skill will recognize that these values can be appropriately adjusted to determine corresponding identity of proteins encoded by two nucleotide sequences by taking into account codon degeneracy, amino acid similarity, reading frame positioning and the like. Substantial identity of amino acid sequences for these purposes normally means sequence identity of between 55-100%, preferably at least 55%, preferably at least 60%, more preferably at least 70%, 80%, 90%, and most preferably at least 95%. 
     Another indication that nucleotide sequences are substantially identical is if two molecules hybridize to each other under stringent conditions. The degeneracy of the genetic code allows for many amino acids substitutions that lead to variety in the nucleotide sequence that code for the same amino acid, hence it is possible that the DNA sequence could code for the same polypeptide but not hybridize to each other under stringent conditions. This may occur, e.g., when a copy of a nucleic acid is created using the maximum codon degeneracy permitted by the genetic code. One indication that two nucleic acid sequences are substantially identical is that the polypeptide, which the first nucleic acid encodes, is immunologically cross reactive with the polypeptide encoded by the second nucleic acid. 
     The terms “substantial identity” in the context of a peptide indicates that a peptide comprises a sequence with between 55-100% sequence identity to a reference sequence preferably at least 55% sequence identity, preferably 60% preferably 70%, more preferably 80%, most preferably at least 90% or 95% sequence identity to the reference sequence over a specified comparison window. Preferably, optimal alignment is conducted using the homology alignment algorithm of Needleman and Wunsch, supra. An indication that two peptide sequences are substantially identical is that one peptide is immunologically reactive with antibodies raised against the second peptide. Thus, a peptide is substantially identical to a second peptide, for example, where the two peptides differ only by a conservative substitution. In addition, a peptide can be substantially identical to a second peptide when they differ by a non-conservative change if the epitope that the antibody recognizes is substantially identical. Peptides, which are “substantially similar” share sequences as, noted above except that residue positions, which are not identical, may differ by conservative amino acid changes. 
     The invention discloses nitrate uptake-associated polynucleotides and polypeptides. The novel nucleotides and proteins of the invention have an expression pattern which indicates that they enhance nitrogen uptake and utilization and thus play an important role in plant development. The polynucleotides are expressed in various plant tissues. The polynucleotides and polypeptides thus provide an opportunity to manipulate plant development to alter tissue development, timing or composition. This may be used to create a plant with enhanced yield under limited nitrogen supply. 
     Nucleic Acids 
     The present invention provides, inter alia, isolated nucleic acids of RNA, DNA, homologs, paralogs and orthologs and/or chimeras thereof, comprising a nitrate uptake-associated polynucleotide. This includes naturally occurring as well as synthetic variants and homologs of the sequences. 
     Sequences homologous, i.e., that share significant sequence identity or similarity, to those provided herein derived from maize,  Arabidopsis thaliana  or from other plants of choice, are also an aspect of the invention. Homologous sequences can be derived from any plant including monocots and dicots and in particular agriculturally important plant species, including but not limited to, crops such as soybean, wheat, corn (maize), potato, cotton, rice, rape, oilseed rape (including canola), sunflower, alfalfa, clover, sugarcane, and turf; or fruits and vegetables, such as banana, blackberry, blueberry, strawberry, and raspberry, cantaloupe, carrot, cauliflower, coffee, cucumber, eggplant, grapes, honeydew, lettuce, mango, melon, onion, papaya, peas, peppers, pineapple, pumpkin, spinach, squash, sweet corn, tobacco, tomato, tomatillo, watermelon, rosaceous fruits (such as apple, peach, pear, cherry and plum) and vegetable brassicas (such as broccoli, cabbage, cauliflower, Brussels sprouts, and kohlrabi). Other crops, including fruits and vegetables, whose phenotype can be changed and which comprise homologous sequences include barley; rye; millet; sorghum; currant; avocado; citrus fruits such as oranges, lemons, grapefruit and tangerines, artichoke, cherries; nuts such as the walnut and peanut; endive; leek; roots such as arrowroot, beet, cassaya, turnip, radish, yarn, and sweet potato; and beans. The homologous sequences may also be derived from woody species, such pine, poplar and eucalyptus, or mint or other labiates. In addition, homologous sequences may be derived from plants that are evolutionarily-related to crop plants, but which may not have yet been used as crop plants. Examples include deadly nightshade ( Atropa belladona ), related to tomato; jimson weed ( Datura strommium ), related to peyote; and teosinte ( Zea  species), related to corn (maize). 
     Orthologs and Paralogs 
     Homologous sequences as described above can comprise orthologous or paralogous sequences. Several different methods are known by those of skill in the art for identifying and defining these functionally homologous sequences. Three general methods for defining orthologs and paralogs are described; an ortholog, paralog or homolog may be identified by one or more of the methods described below. 
     Orthologs and paralogs are evolutionarily related genes that have similar sequence and similar functions. Orthologs are structurally related genes in different species that are derived by a speciation event. Paralogs are structurally related genes within a single species that are derived by a duplication event. 
     Within a single plant species, gene duplication may cause two copies of a particular gene, giving rise to two or more genes with similar sequence and often similar function known as paralogs. A paralog is therefore a similar gene formed by duplication within the same species. Paralogs typically cluster together or in the same clade (a group of similar genes) when a gene family phylogeny is analyzed using programs such as CLUSTAL (Thompson et al. (1994) Nucleic Acids Res. 22: 4673-4680; Higgins et al. (1996) Methods Enzymol. 266: 383-402). Groups of similar genes can also be identified with pair-wise BLAST analysis (Feng and Doolittle (1987) J. Mol. Evol. 25: 351-360). 
     For example, a clade of very similar MADS domain transcription factors from  Arabidopsis  all share a common function in flowering time (Ratcliffe et al. (2001) Plant Physiol. 126: 122-132), and a group of very similar AP2 domain transcription factors from  Arabidopsis  are involved in tolerance of plants to freezing (Gilmour et al. (1998) Plant J. 16: 433-442). Analysis of groups of similar genes with similar function that fall within one clade can yield sub-sequences that are particular to the clade. These sub-sequences, known as consensus sequences, can not only be used to define the sequences within each clade, but define the functions of these genes; genes within a clade may contain paralogous sequences, or orthologous sequences that share the same function (see also, for example, Mount (2001), in Bioinformatics: Sequence and Genome Analysis Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., page 543.) 
     Speciation, the production of new species from a parental species, can also give rise to two or more genes with similar sequence and similar function. These genes, termed orthologs, often have an identical function within their host plants and are often interchangeable between species without losing function. Because plants have common ancestors, many genes in any plant species will have a corresponding orthologous gene in another plant species. Once a phylogenic tree for a gene family of one species has been constructed using a program such as CLUSTAL (Thompson et al. (1994) Nucleic Acids Res. 22: 4673-4680; Higgins et al. (1996) supra) potential orthologous sequences can be placed into the phylogenetic tree and their relationship to genes from the species of interest can be determined. Orthologous sequences can also be identified by a reciprocal BLAST strategy. Once an orthologous sequence has been identified, the function of the ortholog can be deduced from the identified function of the reference sequence. 
     Orthologous genes from different organisms have highly conserved functions, and very often essentially identical functions (Lee et al. (2002) Genome Res. 12: 493-502; Remm et al. (2001) J. Mol. Biol. 314: 1041-1052). Paralogous genes, which have diverged through gene duplication, may retain similar functions of the encoded proteins. In such cases, paralogs can be used interchangeably with respect to certain embodiments of the instant invention (for example, transgenic expression of a coding sequence). 
     Variant Nucleotide Sequences in the Non-Coding Regions 
     The nitrate uptake-associated nucleotide sequences are used to generate variant nucleotide sequences having the nucleotide sequence of the 5′-untranslated region, 3′-untranslated region, or promoter region that is approximately 70%, 75%, 80%, 85%, 90% and 95% identical to the original nucleotide sequence of the corresponding SEQ ID NO:1. These variants are then associated with natural variation in the germplasm for component traits related to NUE. The associated variants are used as marker haplotypes to select for the desirable traits. 
     Variant Amino Acid Sequences of Nitrate Uptake-Associated Polypeptides 
     Variant amino acid sequences of the Nitrate uptake associated polypeptides are generated. In this example, one amino acid is altered. Specifically, the open reading frames are reviewed to determine the appropriate amino acid alteration. The selection of the amino acid to change is made by consulting the protein alignment (with the other orthologs and other gene family members from various species). An amino acid is selected that is deemed not to be under high selection pressure (not highly conserved) and which is rather easily substituted by an amino acid with similar chemical characteristics (i.e., similar functional side-chain). Using a protein alignment, an appropriate amino acid can be changed. Once the targeted amino acid is identified, the procedure outlined herein is followed. Variants having about 70%, 75%, 80%, 85%, 90% and 95% nucleic acid sequence identity are generated using this method. These variants are then associated with natural variation in the germplasm for component traits related to NUE. The associated variants are used as marker haplotypes to select for the desirable traits. 
     The present invention also includes polynucleotides optimized for expression in different organisms. For example, for expression of the polynucleotide in a maize plant, the sequence can be altered to account for specific codon preferences and to alter GC content as according to Murray, et al, supra. Maize codon usage for 28 genes from maize plants is listed in Table 4 of Murray, et al., supra. 
     The nitrate uptake-associated nucleic acids of the present invention comprise isolated nitrate uptake-associated polynucleotides which are inclusive of:
         (a) a polynucleotide encoding a nitrate uptake-associated polypeptide and conservatively modified and polymorphic variants thereof;   (b) a polynucleotide having at least 70% sequence identity with polynucleotides of (a) or (b);   (c) complementary sequences of polynucleotides of (a) or (b).       

     Construction of Nucleic Acids 
     The isolated nucleic acids of the present invention can be made using (a) standard recombinant methods, (b) synthetic techniques, or combinations thereof. In some embodiments, the polynucleotides of the present invention will be cloned, amplified, or otherwise constructed from a fungus or bacteria. 
     The nucleic acids may conveniently comprise sequences in addition to a polynucleotide of the present invention. For example, a multi-cloning site comprising one or more endonuclease restriction sites may be inserted into the nucleic acid to aid in isolation of the polynucleotide. Also, translatable sequences may be inserted to aid in the isolation of the translated polynucleotide of the present invention. For example, a hexa-histidine marker sequence provides a convenient means to purify the proteins of the present invention. The nucleic acid of the present invention—excluding the polynucleotide sequence—is optionally a vector, adapter, or linker for cloning and/or expression of a polynucleotide of the present invention. Additional sequences may be added to such cloning and/or expression sequences to optimize their function in cloning and/or expression, to aid in isolation of the polynucleotide, or to improve the introduction of the polynucleotide into a cell. Typically, the length of a nucleic acid of the present invention less the length of its polynucleotide of the present invention is less than 20 kilobase pairs, often less than 15 kb, and frequently less than 10 kb. Use of cloning vectors, expression vectors, adapters, and linkers is well known in the art. Exemplary nucleic acids include such vectors as: M13, lambda ZAP Express, lambda ZAP II, lambda gt10, lambda gt11, pBK-CMV, pBK-RSV, pBluescript II, lambda DASH II, lambda EMBL 3, lambda EMBL 4, pWE15, SuperCos 1, SurfZap, Uni-ZAP, pBC, pBS+/−, pSG5, pBK, pCR-Script, pET, pSPUTK, p3′SS, pGEM, pSK+/−, pGEX, pSPORTI and II, pOPRSVI CAT, pOPI3 CAT, pXT1, pSG5, pPbac, pMbac, pMC1neo, pOG44, pOG45, pFRTβGAL, pNEOβGAL, pRS403, pRS404, pRS405, pRS406, pRS413, pRS414, pRS415, pRS416, lambda MOSSIox, and lambda MOSEIox. Optional vectors for the present invention, include but are not limited to, lambda ZAP II, and pGEX. For a description of various nucleic acids see, e.g., Stratagene Cloning Systems, Catalogs 1995, 1996, 1997 (La Jolla, Calif.); and, Amersham Life Sciences, Inc, Catalog &#39;97 (Arlington Heights, Ill.). 
     Synthetic Methods for Constructing Nucleic Acids 
     The isolated nucleic acids of the present invention can also be prepared by direct chemical synthesis by methods such as the phosphotriester method of Narang, et al., (1979)  Meth. Enzymol.  68:90-9; the phosphodiester method of Brown, et al., (1979)  Meth. Enzymol.  68:109-51; the diethylphosphoramidite method of Beaucage, et al., (1981)  Tetra. Letts.  22(20):1859-62; the solid phase phosphoramidite triester method described by Beaucage, et al., supra, e.g., using an automated synthesizer, e.g., as described in Needham-VanDevanter, et al., (1984)  Nucleic Acids Res.  12:6159-68; and, the solid support method of U.S. Pat. No. 4,458,066. Chemical synthesis generally produces a single stranded oligonucleotide. This may be converted into double stranded DNA by hybridization with a complementary sequence or by polymerization with a DNA polymerase using the single strand as a template. One of skill will recognize that while chemical synthesis of DNA is limited to sequences of about 100 bases, longer sequences may be obtained by the ligation of shorter sequences. 
     UTRs and Codon Preference 
     In general, translational efficiency has been found to be regulated by specific sequence elements in the 5′ non-coding or untranslated region (5′ UTR) of the RNA. Positive sequence motifs include translational initiation consensus sequences (Kozak, (1987)  Nucleic Acids Res.  15:8125) and the 5&lt;G&gt; 7 methyl GpppG RNA cap structure (Drummond, et al., (1985)  Nucleic Acids Res.  13:7375). Negative elements include stable intramolecular 5′ UTR stem-loop structures (Muesing, et al., (1987)  Cell  48:691) and AUG sequences or short open reading frames preceded by an appropriate AUG in the 5′ UTR (Kozak, supra, Rao, et al., (1988)  Mol. and Cell. Biol.  8:284). Accordingly, the present invention provides 5′ and/or 3′ UTR regions for modulation of translation of heterologous coding sequences. 
     Further, the polypeptide-encoding segments of the polynucleotides of the present invention can be modified to alter codon usage. Altered codon usage can be employed to alter translational efficiency and/or to optimize the coding sequence for expression in a desired host or to optimize the codon usage in a heterologous sequence for expression in maize. Codon usage in the coding regions of the polynucleotides of the present invention can be analyzed statistically using commercially available software packages such as “Codon Preference” available from the University of Wisconsin Genetics Computer Group. See, Devereaux, et al., (1984)  Nucleic Acids Res.  12:387-395); or MacVector 4.1 (Eastman Kodak Co., New Haven, Conn.). Thus, the present invention provides a codon usage frequency characteristic of the coding region of at least one of the polynucleotides of the present invention. The number of polynucleotides (3 nucleotides per amino acid) that can be used to determine a codon usage frequency can be any integer from 3 to the number of polynucleotides of the present invention as provided herein. Optionally, the polynucleotides will be full-length sequences. An exemplary number of sequences for statistical analysis can be at least 1, 5, 10, 20, 50 or 100. 
     Sequence Shuffling 
     The present invention provides methods for sequence shuffling using polynucleotides of the present invention, and compositions resulting therefrom. Sequence shuffling is described in PCT publication No. 96/19256. See also, Zhang, et al., (1997)  Proc. Natl. Acad. Sci. USA  94:4504-9; and Zhao, et al., (1998)  Nature Biotech  16:258-61. Generally, sequence shuffling provides a means for generating libraries of polynucleotides having a desired characteristic, which can be selected or screened for. Libraries of recombinant polynucleotides are generated from a population of related sequence polynucleotides, which comprise sequence regions, which have substantial sequence identity and can be homologously recombined in vitro or in vivo. The population of sequence-recombined polynucleotides comprises a subpopulation of polynucleotides which possess desired or advantageous characteristics and which can be selected by a suitable selection or screening method. The characteristics can be any property or attribute capable of being selected for or detected in a screening system, and may include properties of: an encoded protein, a transcriptional element, a sequence controlling transcription, RNA processing, RNA stability, chromatin conformation, translation, or other expression property of a gene or transgene, a replicative element, a protein-binding element, or the like, such as any feature which confers a selectable or detectable property. In some embodiments, the selected characteristic will be an altered K m  and/or K cat  over the wild-type protein as provided herein. In other embodiments, a protein or polynucleotide generated from sequence shuffling will have a ligand binding affinity greater than the non-shuffled wild-type polynucleotide. In yet other embodiments, a protein or polynucleotide generated from sequence shuffling will have an altered pH optimum as compared to the non-shuffled wild-type polynucleotide. The increase in such properties can be at least 110%, 120%, 130%, 140% or greater than 150% of the wild-type value. 
     Recombinant Expression Cassettes 
     The present invention further provides recombinant expression cassettes comprising a nucleic acid of the present invention. A nucleic acid sequence coding for the desired polynucleotide of the present invention, for example a cDNA or a genomic sequence encoding a polypeptide long enough to code for an active protein of the present invention, can be used to construct a recombinant expression cassette which can be introduced into the desired host cell. A recombinant expression cassette will typically comprise a polynucleotide of the present invention operably linked to transcriptional initiation regulatory sequences which will direct the transcription of the polynucleotide in the intended host cell, such as tissues of a transformed plant. 
     For example, plant expression vectors may include (1) a cloned plant gene under the transcriptional control of 5′ and 3′ regulatory sequences and (2) a dominant selectable marker. Such plant expression vectors may also contain, if desired, a promoter regulatory region (e.g., one conferring inducible or constitutive, environmentally- or developmentally-regulated, or cell- or tissue-specific/selective expression), a transcription initiation start site, a ribosome binding site, an RNA processing signal, a transcription termination site, and/or a polyadenylation signal. 
     A plant promoter fragment can be employed which will direct expression of a polynucleotide of the present invention in all tissues of a regenerated plant. Such promoters are referred to herein as “constitutive” promoters and are active under most environmental conditions and states of development or cell differentiation. Examples of constitutive promoters include the 1′- or 2′-promoter derived from T-DNA of  Agrobacterium tumefaciens , the Smas promoter, the cinnamyl alcohol dehydrogenase promoter (U.S. Pat. No. 5,683,439), the Nos promoter, the rubisco promoter, the GRP1-8 promoter, the 35S promoter from cauliflower mosaic virus (CaMV), as described in Odell, et al., (1985)  Nature  313:810-2; rice actin (McElroy, et al., (1990)  Plant Cell  163-171); ubiquitin (Christensen, et al., (1992)  Plant Mol. Biol.  12:619-632 and Christensen, et al., (1992)  Plant Mol. Biol.  18:675-89); pEMU (Last, et al., (1991)  Theor. Appl. Genet.  81:581-8); MAS (Velten, et al., (1984)  EMBO J.  3:2723-30); and maize H3 histone (Lepetit, et al., (1992)  Mol. Gen. Genet.  231:276-85; and Atanassvoa, et al., (1992)  Plant Journal  2(3):291-300); ALS promoter, as described in PCT Application No. WO 96/30530; and other transcription initiation regions from various plant genes known to those of skill. For the present invention ubiquitin is the preferred promoter for expression in monocot plants. 
     Alternatively, the plant promoter can direct expression of a polynucleotide of the present invention in a specific tissue or may be otherwise under more precise environmental or developmental control. Such promoters are referred to here as “inducible” promoters. Environmental conditions that may effect transcription by inducible promoters include pathogen attack, anaerobic conditions, or the presence of light. Examples of inducible promoters are the Adh1 promoter, which is inducible by hypoxia or cold stress, the Hsp70 promoter, which is inducible by heat stress, and the PPDK promoter, which is inducible by light. 
     Examples of promoters under developmental control include promoters that initiate transcription only, or preferentially, in certain tissues, such as leaves, roots, fruit, seeds, or flowers. The operation of a promoter may also vary depending on its location in the genome. Thus, an inducible promoter may become fully or partially constitutive in certain locations. 
     If polypeptide expression is desired, it is generally desirable to include a polyadenylation region at the 3′-end of a polynucleotide coding region. The polyadenylation region can be derived from a variety of plant genes, or from T-DNA. The 3′ end sequence to be added can be derived from, for example, the nopaline synthase or octopine synthase genes, or alternatively from another plant gene, or less preferably from any other eukaryotic gene. Examples of such regulatory elements include, but are not limited to, 3′ termination and/or polyadenylation regions such as those of the  Agrobacterium tumefaciens  nopaline synthase (nos) gene (Bevan, et al., (1983)  Nucleic Acids Res.  12:369-85); the potato proteinase inhibitor II (PINII) gene (Keil, et al., (1986)  Nucleic Acids Res.  14:5641-50; and An, et al., (1989)  Plant Cell  1:115-22); and the CaMV 19S gene (Mogen, et al., (1990)  Plant Cell  2:1261-72). 
     An intron sequence can be added to the 5′ untranslated region or the coding sequence of the partial coding sequence to increase the amount of the mature message that accumulates in the cytosol. Inclusion of a spliceable intron in the transcription unit in both plant and animal expression constructs has been shown to increase gene expression at both the mRNA and protein levels up to 1000-fold (Buchman and Berg, (1988)  Mol. Cell Biol.  8:4395-4405; Callis, et al., (1987)  Genes Dev.  1:1183-200). Such intron enhancement of gene expression is typically greatest when placed near the 5′ end of the transcription unit. Use of maize introns Adh1-S intron 1, 2 and 6, the Bronze-1 intron are known in the art. See generally,  The Maize Handbook , Chapter 116, Freeling and Walbot, eds., Springer, N.Y. (1994). 
     Plant signal sequences, including, but not limited to, signal-peptide encoding DNA/RNA sequences which target proteins to the extracellular matrix of the plant cell (Dratewka-Kos, et al., (1989)  J. Biol. Chem.  264:4896-900), such as the  Nicotiana plumbaginifolia  extension gene (DeLoose, et al., (1991)  Gene  99:95-100); signal peptides which target proteins to the vacuole, such as the sweet potato sporamin gene (Matsuka, et al., (1991)  Proc. Natl. Acad. Sci. USA  88:834) and the barley lectin gene (Wilkins, et al., (1990)  Plant Cell,  2:301-13); signal peptides which cause proteins to be secreted, such as that of PRIb (Lind, et al., (1992)  Plant Mol. Biol.  18:47-53) or the barley alpha amylase (BAA) (Rahmatullah, et al., (1989)  Plant Mol. Biol.  12:119, and hereby incorporated by reference), or signal peptides which target proteins to the plastids such as that of rapeseed enoyl-Acp reductase (Verwaert, et al., (1994)  Plant Mol. Biol.  26:189-202) are useful in the invention. 
     The vector comprising the sequences from a polynucleotide of the present invention will typically comprise a marker gene, which confers a selectable phenotype on plant cells. Usually, the selectable marker gene will encode antibiotic resistance, with suitable genes including genes coding for resistance to the antibiotic spectinomycin (e.g., the aada gene), the streptomycin phosphotransferase (SPT) gene coding for streptomycin resistance, the neomycin phosphotransferase (NPTII) gene encoding kanamycin or geneticin resistance, the hygromycin phosphotransferase (HPT) gene coding for hygromycin resistance, genes coding for resistance to herbicides which act to inhibit the action of acetolactate synthase (ALS), in particular the sulfonylurea-type herbicides (e.g., the acetolactate synthase (ALS) gene containing mutations leading to such resistance in particular the S4 and/or Hra mutations), genes coding for resistance to herbicides which act to inhibit action of glutamine synthase, such as phosphinothricin or basta (e.g., the bar gene), or other such genes known in the art. The bar gene encodes resistance to the herbicide basta, and the ALS gene encodes resistance to the herbicide chlorsulfuron. 
     Typical vectors useful for expression of genes in higher plants are well known in the art and include vectors derived from the tumor-inducing (Ti) plasmid of  Agrobacterium tumefaciens  described by Rogers, et al. (1987),  Meth. Enzymol.  153:253-77. These vectors are plant integrating vectors in that on transformation, the vectors integrate a portion of vector DNA into the genome of the host plant. Exemplary  A. tumefaciens  vectors useful herein are plasmids pKYLX6 and pKYLX7 of Schardl, et al., (1987)  Gene  61:1-11, and Berger, et al., (1989)  Proc. Natl. Acad. Sci. USA,  86:8402-6. Another useful vector herein is plasmid p61101.2 that is available from CLONTECH Laboratories, Inc. (Palo Alto, Calif.). 
     Expression of Proteins in Host Cells 
     Using the nucleic acids of the present invention, one may express a protein of the present invention in a recombinantly engineered cell such as bacteria, yeast, insect, mammalian, or preferably plant cells. The cells produce the protein in a non-natural condition (e.g., in quantity, composition, location, and/or time), because they have been genetically altered through human intervention to do so. 
     It is expected that those of skill in the art are knowledgeable in the numerous expression systems available for expression of a nucleic acid encoding a protein of the present invention. No attempt to describe in detail the various methods known for the expression of proteins in prokaryotes or eukaryotes will be made. 
     In brief summary, the expression of isolated nucleic acids encoding a protein of the present invention will typically be achieved by operably linking, for example, the DNA or cDNA to a promoter (which is either constitutive or inducible), followed by incorporation into an expression vector. The vectors can be suitable for replication and integration in either prokaryotes or eukaryotes. Typical expression vectors contain transcription and translation terminators, initiation sequences, and promoters useful for regulation of the expression of the DNA encoding a protein of the present invention. To obtain high level expression of a cloned gene, it is desirable to construct expression vectors which contain, at the minimum, a strong promoter, such as ubiquitin, to direct transcription, a ribosome binding site for translational initiation, and a transcription/translation terminator. Constitutive promoters are classified as providing for a range of constitutive expression. Thus, some are weak constitutive promoters, and others are strong constitutive promoters. Generally, by “weak promoter” is intended a promoter that drives expression of a coding sequence at a low level. By “low level” is intended at levels of about 1/10,000 transcripts to about 1/100,000 transcripts to about 1/500,000 transcripts. Conversely, a “strong promoter” drives expression of a coding sequence at a “high level,” or about 1/10 transcripts to about 1/100 transcripts to about 1/1,000 transcripts. 
     One of skill would recognize that modifications could be made to a protein of the present invention without diminishing its biological activity. Some modifications may be made to facilitate the cloning, expression, or incorporation of the targeting molecule into a fusion protein. Such modifications are well known to those of skill in the art and include, for example, a methionine added at the amino terminus to provide an initiation site, or additional amino acids (e.g., poly His) placed on either terminus to create conveniently located restriction sites or termination codons or purification sequences. 
     Expression in Prokaryotes 
     Prokaryotic cells may be used as hosts for expression. Prokaryotes most frequently are represented by various strains of  E. coli ; however, other microbial strains may also be used. Commonly used prokaryotic control sequences which are defined herein to include promoters for transcription initiation, optionally with an operator, along with ribosome binding site sequences, include such commonly used promoters as the beta lactamase (penicillinase) and lactose (lac) promoter systems (Chang, et al., (1977)  Nature  198:1056), the tryptophan (trp) promoter system (Goeddel, et al., (1980)  Nucleic Acids Res.  8:4057) and the lambda derived P L promoter and N-gene ribosome binding site (Shimatake, et al., (1981)  Nature  292:128). The inclusion of selection markers in DNA vectors transfected in  E. coli  is also useful. Examples of such markers include genes specifying resistance to ampicillin, tetracycline, or chloramphenicol. 
     The vector is selected to allow introduction of the gene of interest into the appropriate host cell. Bacterial vectors are typically of plasmid or phage origin. Appropriate bacterial cells are infected with phage vector particles or transfected with naked phage vector DNA. If a plasmid vector is used, the bacterial cells are transfected with the plasmid vector DNA. Expression systems for expressing a protein of the present invention are available using  Bacillus  sp. and  Salmonella  (Palva, et al., (1983)  Gene  22:229-35; Mosbach, et al., (1983)  Nature  302:543-5). The pGEX-4T-1 plasmid vector from Pharmacia is the preferred  E. coli  expression vector for the present invention. 
     Expression in Eukaryotes 
     A variety of eukaryotic expression systems such as yeast, insect cell lines, plant and mammalian cells, are known to those of skill in the art. As explained briefly below, the present invention can be expressed in these eukaryotic systems. In some embodiments, transformed/transfected plant cells, as discussed infra, are employed as expression systems for production of the proteins of the instant invention. 
     Synthesis of heterologous proteins in yeast is well known. Sherman, et al., (1982)  Methods in Yeast Genetics , Cold Spring Harbor Laboratory is a well recognized work describing the various methods available to produce the protein in yeast. Two widely utilized yeasts for production of eukaryotic proteins are  Saccharomyces cerevisiae  and  Pichia pastoris . Vectors, strains, and protocols for expression in  Saccharomyces  and  Pichia  are known in the art and available from commercial suppliers (e.g., Invitrogen). Suitable vectors usually have expression control sequences, such as promoters, including 3-phosphoglycerate kinase or alcohol oxidase, and an origin of replication, termination sequences and the like as desired. 
     A protein of the present invention, once expressed, can be isolated from yeast by lysing the cells and applying standard protein isolation techniques to the lysates or the pellets. The monitoring of the purification process can be accomplished by using Western blot techniques or radioimmunoassay of other standard immunoassay techniques. 
     The sequences encoding proteins of the present invention can also be ligated to various expression vectors for use in transfecting cell cultures of, for instance, mammalian, insect, or plant origin. Mammalian cell systems often will be in the form of monolayers of cells although mammalian cell suspensions may also be used. A number of suitable host cell lines capable of expressing intact proteins have been developed in the art, and include the HEK293, BHK21, and CHO cell lines. Expression vectors for these cells can include expression control sequences, such as an origin of replication, a promoter (e.g., the CMV promoter, a HSV tk promoter or pgk (phosphoglycerate kinase) promoter), an enhancer (Queen, et al., (1986)  Immunol. Rev.  89:49), and necessary processing information sites, such as ribosome binding sites, RNA splice sites, polyadenylation sites (e.g., an SV40 large T Ag poly A addition site), and transcriptional terminator sequences. Other animal cells useful for production of proteins of the present invention are available, for instance, from the American Type Culture Collection Catalogue of Cell Lines and Hybridomas (7 th  ed., 1992). 
     Appropriate vectors for expressing proteins of the present invention in insect cells are usually derived from the SF9 baculovirus. Suitable insect cell lines include mosquito larvae, silkworm, armyworm, moth, and  Drosophila  cell lines such as a Schneider cell line (see, e.g., Schneider, (1987)  J. Embryol. Exp. Morphol.  27:353-65). 
     As with yeast, when higher animal or plant host cells are employed, polyadenlyation or transcription terminator sequences are typically incorporated into the vector. An example of a terminator sequence is the polyadenlyation sequence from the bovine growth hormone gene. Sequences for accurate splicing of the transcript may also be included. An example of a splicing sequence is the VP1 intron from SV40 (Sprague et al.,  J. Virol.  45:773-81 (1983)). Additionally, gene sequences to control replication in the host cell may be incorporated into the vector such as those found in bovine papilloma virus type-vectors (Saveria-Campo, “Bovine Papilloma Virus DNA a Eukaryotic Cloning Vector,” in  DNA Cloning: A Practical Approach , vol. II, Glover, ed., IRL Press, Arlington, Va., pp. 213-38 (1985)). 
     In addition, the nitrate uptake-associated gene placed in the appropriate plant expression vector can be used to transform plant cells. The polypeptide can then be isolated from plant callus or the transformed cells can be used to regenerate transgenic plants. Such transgenic plants can be harvested, and the appropriate tissues (seed or leaves, for example) can be subjected to large scale protein extraction and purification techniques. 
     Plant Transformation Methods 
     Numerous methods for introducing foreign genes into plants are known and can be used to insert a nitrate uptake-associated polynucleotide into a plant host, including biological and physical plant transformation protocols. See, e.g., Miki et al., “Procedure for Introducing Foreign DNA into Plants,” in  Methods in Plant Molecular Biology and Biotechnology , Glick and Thompson, eds., CRC Press, Inc., Boca Raton, pp. 67-88 (1993). The methods chosen vary with the host plant, and include chemical transfection methods such as calcium phosphate, microorganism-mediated gene transfer such as  Agrobacterium  (Horsch et al.,  Science  227:1229-31 (1985)), electroporation, micro-injection, and biolistic bombardment. 
     Expression cassettes and vectors and in vitro culture methods for plant cell or tissue transformation and regeneration of plants are known and available. See, e.g., Gruber et al., “Vectors for Plant Transformation,” in  Methods in Plant Molecular Biology and Biotechnology , supra, pp. 89-119. 
     The isolated polynucleotides or polypeptides may be introduced into the plant by one or more techniques typically used for direct delivery into cells. Such protocols may vary depending on the type of organism, cell, plant or plant cell, i.e. monocot or dicot, targeted for gene modification. Suitable methods of transforming plant cells include microinjection (Crossway, et al., (1986)  Biotechniques  4:320-334; and U.S. Pat. No. 6,300,543), electroporation (Riggs, et al., (1986)  Proc. Natl. Acad. Sci. USA  83:5602-5606, direct gene transfer (Paszkowski et al., (1984)  EMBO J.  3:2717-2722), and ballistic particle acceleration (see, for example, Sanford, et al., U.S. Pat. No. 4,945,050; WO 91/10725; and McCabe, et al., (1988)  Biotechnology  6:923-926). Also see, Tomes, et al., “Direct DNA Transfer into Intact Plant Cells Via Microprojectile Bombardment”. pp. 197-213 in  Plant Cell, Tissue and Organ Culture, Fundamental Methods . eds. O. L. Gamborg &amp; G. C. Phillips. Springer-Verlag Berlin Heidelberg New York, 1995; U.S. Pat. No. 5,736,369 (meristem); Weissinger, et al., (1988)  Ann. Rev. Genet.  22:421-477; Sanford, et al., (1987)  Particulate Science and Technology  5:27-37 (onion); Christou, et al., (1988)  Plant Physiol.  87:671-674 (soybean); Datta, et al., (1990)  Biotechnology  8:736-740 (rice); Klein, et al., (1988)  Proc. Natl. Acad. Sci. USA  85:4305-4309 (maize); Klein, et al., (1988)  Biotechnology  6:559-563 (maize); WO 91/10725 (maize); Klein, et al., (1988)  Plant Physiol.  91:440-444 (maize); Fromm, et al., (1990)  Biotechnology  8:833-839; and Gordon-Kamm, et al., (1990)  Plant Cell  2:603-618 (maize); Hooydaas-Van Slogteren &amp; Hooykaas (1984)  Nature  (London) 311:763-764; Bytebierm, et al., (1987)  Proc. Natl. Acad. Sci. USA  84:5345-5349 (Liliaceae); De Wet, et al., (1985)  In The Experimental Manipulation of Ovule Tissues , ed. G. P. Chapman, et al., pp. 197-209. Longman, N.Y. (pollen); Kaeppler, et al., (1990)  Plant Cell Reports  9:415-418; and Kaeppler, et al., (1992)  Theor. Appl. Genet.  84:560-566 (whisker-mediated transformation); U.S. Pat. No. 5,693,512 (sonication); D&#39;Halluin, et al., (1992)  Plant Cell  4:1495-1505 (electroporation); Li, et al., (1993)  Plant Cell Reports  12:250-255; and Christou and Ford, (1995)  Annals of Botany  75:407-413 (rice); Osjoda, et al., (1996)  Nature Biotech.  14:745-750;  Agrobacterium  mediated maize transformation (U.S. Pat. No. 5,981,840); silicon carbide whisker methods (Frame, et al., (1994)  Plant J.  6:941-948); laser methods (Guo, et al., (1995)  Physiologia Plantarum  93:19-24); sonication methods (Bao, et al., (1997)  Ultrasound in Medicine  &amp;  Biology  23:953-959; Finer and Finer, (2000)  Lett Appl Microbiol.  30:406-10; Amoah, et al., (2001)  J Exp Bot  52:1135-42); polyethylene glycol methods (Krens, et al., (1982)  Nature  296:72-77); protoplasts of monocot and dicot cells can be transformed using electroporation (Fromm, et al., (1985)  Proc. Natl. Acad. Sci. USA  82:5824-5828) and microinjection (Crossway, et al., (1986)  Mol. Gen. Genet.  202:179-185); all of which are herein incorporated by reference. 
       Agrobacterium -Mediated Transformation 
     The most widely utilized method for introducing an expression vector into plants is based on the natural transformation system of  Agrobacterium. A. tumefaciens  and  A. rhizogenes  are plant pathogenic soil bacteria, which genetically transform plant cells. The Ti and Ri plasmids of  A. tumefaciens  and  A. rhizogenes , respectively, carry genes responsible for genetic transformation of plants. See, e.g., Kado, (1991)  Crit. Rev. Plant Sci.  10:1. Descriptions of the  Agrobacterium  vector systems and methods for  Agrobacterium -mediated gene transfer are provided in Gruber, et al., supra; Miki, et al., supra; and Moloney, et al., (1989)  Plant Cell Reports  8:238. 
     Similarly, the gene can be inserted into the T-DNA region of a Ti or Ri plasmid derived from  A. tumefaciens  or  A. rhizogenes , respectively. Thus, expression cassettes can be constructed as above, using these plasmids. Many control sequences are known which when coupled to a heterologous coding sequence and transformed into a host organism show fidelity in gene expression with respect to tissue/organ specificity of the original coding sequence. See, e.g., Benfey and Chua, (1989)  Science  244:174-81. Particularly suitable control sequences for use in these plasmids are promoters for constitutive leaf-specific expression of the gene in the various target plants. Other useful control sequences include a promoter and terminator from the nopaline synthase gene (NOS). The NOS promoter and terminator are present in the plasmid pARC2, available from the American Type Culture Collection and designated ATCC 67238. If such a system is used, the virulence (vir) gene from either the Ti or Ri plasmid must also be present, either along with the T-DNA portion, or via a binary system where the vir gene is present on a separate vector. Such systems, vectors for use therein, and methods of transforming plant cells are described in U.S. Pat. No. 4,658,082; U.S. patent application Ser. No. 913,914, filed Oct. 1, 1986, as referenced in U.S. Pat. No. 5,262,306, issued Nov. 16, 1993; and Simpson, et al., (1986) Plant Mol. Biol. 6:403-15 (also referenced in the &#39;306 patent); all incorporated by reference in their entirety. 
     Once constructed, these plasmids can be placed into  A. rhizogenes  or  A. tumefaciens  and these vectors used to transform cells of plant species, which are ordinarily susceptible to  Fusarium  or  Alternaria  infection. Several other transgenic plants are also contemplated by the present invention including but not limited to soybean, corn, sorghum, alfalfa, rice, clover, cabbage, banana, coffee, celery, tobacco, cowpea, cotton, melon and pepper. The selection of either  A. tumefaciens  or  A. rhizogenes  will depend on the plant being transformed thereby. In general  A. tumefaciens  is the preferred organism for transformation. Most dicotyledonous plants, some gymnosperms, and a few monocotyledonous plants (e.g., certain members of the Liliales and Arales) are susceptible to infection with  A. tumefaciens. A. rhizogenes  also has a wide host range, embracing most dicots and some gymnosperms, which includes members of the Leguminosae, Compositae, and Chenopodiaceae. Monocot plants can now be transformed with some success. European Patent Application No. 604 662 A1 discloses a method for transforming monocots using  Agrobacterium . European Application No. 672 752 A1 discloses a method for transforming monocots with  Agrobacterium  using the scutellum of immature embryos. Ishida, et al., discuss a method for transforming maize by exposing immature embryos to  A. tumefaciens  ( Nature Biotechnology  14:745-50 (1996)). 
     Once transformed, these cells can be used to regenerate transgenic plants. For example, whole plants can be infected with these vectors by wounding the plant and then introducing the vector into the wound site. Any part of the plant can be wounded, including leaves, stems and roots. Alternatively, plant tissue, in the form of an explant, such as cotyledonary tissue or leaf disks, can be inoculated with these vectors, and cultured under conditions, which promote plant regeneration. Roots or shoots transformed by inoculation of plant tissue with  A. rhizogenes  or  A. tumefaciens , containing the gene coding for the fumonisin degradation enzyme, can be used as a source of plant tissue to regenerate fumonisin-resistant transgenic plants, either via somatic embryogenesis or organogenesis. Examples of such methods for regenerating plant tissue are disclosed in Shahin, (1985)  Theor. Appl. Genet.  69:235-40; U.S. Pat. No. 4,658,082; Simpson, et al., supra; and U.S. patent application Ser. Nos. 913,913 and 913,914, both filed Oct. 1, 1986, as referenced in U.S. Pat. No. 5,262,306, issued Nov. 16, 1993, the entire disclosures therein incorporated herein by reference. 
     Direct Gene Transfer 
     Despite the fact that the host range for  Agrobacterium -mediated transformation is broad, some major cereal crop species and gymnosperms have generally been recalcitrant to this mode of gene transfer, even though some success has recently been achieved in rice (Hiei, et al., (1994)  The Plant Journal  6:271-82). Several methods of plant transformation, collectively referred to as direct gene transfer, have been developed as an alternative to  Agrobacterium -mediated transformation. 
     A generally applicable method of plant transformation is microprojectile-mediated transformation, where DNA is carried on the surface of microprojectiles measuring about 1 to 4 μm. The expression vector is introduced into plant tissues with a biolistic device that accelerates the microprojectiles to speeds of 300 to 600 m/s which is sufficient to penetrate the plant cell walls and membranes (Sanford, et al., (1987)  Part. Sci. Technol.  5:27; Sanford, (1988)  Trends Biotech  6:299; Sanford, (1990)  Physiol. Plant  79:206; and Klein, et al., (1992)  Biotechnology  10:268). 
     Another method for physical delivery of DNA to plants is sonication of target cells as described in Zang, et al., (1991)  BioTechnology  9:996. Alternatively, liposome or spheroplast fusions have been used to introduce expression vectors into plants. See, e.g., Deshayes, et al., (1985)  EMBO J.  4:2731; and Christou, et al., (1987)  Proc. Natl. Acad. Sci. USA  84:3962. Direct uptake of DNA into protoplasts using CaCl 2  precipitation, polyvinyl alcohol, or poly-L-ornithine has also been reported. See, e.g., Hain, et al., (1985)  Mol. Gen. Genet.  199:161; and Draper, et al., (1982)  Plant Cell Physiol.  23:451. 
     Electroporation of protoplasts and whole cells and tissues has also been described. See, e.g., Donn, et al., (1990)  Abstracts of the VIIth Int&#39;l. Congress on Plant Cell and Tissue Culture IAPTC , A2-38, p. 53; D′Halluin, et al., (1992)  Plant Cell  4:1495-505; and Spencer, et al., (1994)  Plant Mol. Biol.  24:51-61. 
     Increasing the Activity and/or Level of a Nitrate Uptake-Associated Polypeptide 
     Methods are provided to increase the activity and/or level of the nitrate uptake-associated polypeptide of the invention. An increase in the level and/or activity of the nitrate uptake-associated polypeptide of the invention can be achieved by providing to the plant a nitrate uptake-associated polypeptide. The nitrate uptake-associated polypeptide can be provided by introducing the amino acid sequence encoding the nitrate uptake-associated polypeptide into the plant, introducing into the planta nucleotide sequence encoding a nitrate uptake-associated polypeptide or alternatively by modifying a genomic locus encoding the nitrate uptake-associated polypeptide of the invention. 
     As discussed elsewhere herein, many methods are known the art for providing a polypeptide to a plant including, but not limited to, direct introduction of the polypeptide into the plant, introducing into the plant (transiently or stably) a polynucleotide construct encoding a polypeptide having enhanced nitrogen utilization activity. It is also recognized that the methods of the invention may employ a polynucleotide that is not capable of directing, in the transformed plant, the expression of a protein or RNA. Thus, the level and/or activity of a nitrate uptake-associated polypeptide may be increased by altering the gene encoding the nitrate uptake-associated polypeptide or its promoter. See, e.g., Kmiec, U.S. Pat. No. 5,565,350; Zarling, et al., PCT/US93/03868. Therefore, mutagenized plants that carry mutations in nitrate uptake-associated genes, where the mutations increase expression of the nitrate uptake-associated gene or increase the nitrate uptake-associated activity of the encoded nitrate uptake-associated polypeptide are provided. 
     Reducing the Activity and/or Level of a Nitrate Uptake-Associated Polypeptide 
     Methods are provided to reduce or eliminate the activity of a nitrate uptake-associated polypeptide of the invention by transforming a plant cell with an expression cassette that expresses a polynucleotide that inhibits the expression of the nitrate uptake-associated polypeptide. The polynucleotide may inhibit the expression of the nitrate uptake-associated polypeptide directly, by preventing transcription or translation of the nitrate uptake-associated messenger RNA, or indirectly, by encoding a polypeptide that inhibits the transcription or translation of a nitrate uptake-associated gene encoding nitrate uptake-associated polypeptide. Methods for inhibiting or eliminating the expression of a gene in a plant are well known in the art, and any such method may be used in the present invention to inhibit the expression of nitrate uptake-associated polypeptide. Many methods may be used to reduce or eliminate the activity of a nitrate uptake-associated polypeptide. In addition, more than one method may be used to reduce the activity of a single nitrate uptake-associated polypeptide. 
     1. Polynucleotide-Based Methods: 
     In some embodiments of the present invention, a plant is transformed with an expression cassette that is capable of expressing a polynucleotide that inhibits the expression of a nitrate uptake-associated polypeptide of the invention. The term “expression” as used herein refers to the biosynthesis of a gene product, including the transcription and/or translation of said gene product. For example, for the purposes of the present invention, an expression cassette capable of expressing a polynucleotide that inhibits the expression of at least one nitrate uptake-associated polypeptide is an expression cassette capable of producing an RNA molecule that inhibits the transcription and/or translation of at least one nitrate uptake-associated polypeptide of the invention. The “expression” or “production” of a protein or polypeptide from a DNA molecule refers to the transcription and translation of the coding sequence to produce the protein or polypeptide, while the “expression” or “production” of a protein or polypeptide from an RNA molecule refers to the translation of the RNA coding sequence to produce the protein or polypeptide. 
     Examples of polynucleotides that inhibit the expression of a nitrate uptake-associated polypeptide are given below. 
     i. Sense Suppression/Cosuppression 
     In some embodiments of the invention, inhibition of the expression of a nitrate uptake-associated polypeptide may be obtained by sense suppression or cosuppression. For cosuppression, an expression cassette is designed to express an RNA molecule corresponding to all or part of a messenger RNA encoding a nitrate uptake-associated polypeptide in the “sense” orientation. Over expression of the RNA molecule can result in reduced expression of the native gene. Accordingly, multiple plant lines transformed with the cosuppression expression cassette are screened to identify those that show the greatest inhibition of nitrate uptake-associated polypeptide expression. 
     The polynucleotide used for cosuppression may correspond to all or part of the sequence encoding the nitrate uptake-associated polypeptide, all or part of the 5′ and/or 3′ untranslated region of a nitrate uptake-associated polypeptide transcript, or all or part of both the coding sequence and the untranslated regions of a transcript encoding a nitrate uptake-associated polypeptide. In some embodiments where the polynucleotide comprises all or part of the coding region for the nitrate uptake-associated polypeptide, the expression cassette is designed to eliminate the start codon of the polynucleotide so that no protein product will be translated. 
     Cosuppression may be used to inhibit the expression of plant genes to produce plants having undetectable protein levels for the proteins encoded by these genes. See, for example, Broin, et al., (2002)  Plant Cell  14:1417-1432. Cosuppression may also be used to inhibit the expression of multiple proteins in the same plant. See, for example, U.S. Pat. No. 5,942,657. Methods for using cosuppression to inhibit the expression of endogenous genes in plants are described in Flavell, et al., (1994)  Proc. Natl. Acad. Sci. USA  91:3490-3496; Jorgensen, et al., (1996)  Plant Mol. Biol.  31:957-973; Johansen and Carrington, (2001)  Plant Physiol.  126:930-938; Broin, et al., (2002)  Plant Cell  14:1417-1432; Stoutjesdijk, et al., (2002)  Plant Physiol.  129:1723-1731; Yu, et al., (2003)  Phytochemistry  63:753-763; and U.S. Pat. Nos. 5,034,323, 5,283,184, and 5,942,657; each of which is herein incorporated by reference. The efficiency of cosuppression may be increased by including a poly-dT region in the expression cassette at a position 3′ to the sense sequence and 5′ of the polyadenylation signal. See, U.S. Patent Publication No. 2002/0048814, herein incorporated by reference. Typically, such a nucleotide sequence has substantial sequence identity to the sequence of the transcript of the endogenous gene, optimally greater than about 65% sequence identity, more optimally greater than about 85% sequence identity, most optimally greater than about 95% sequence identity. See U.S. Pat. Nos. 5,283,184 and 5,034,323; herein incorporated by reference. 
     ii. Antisense Suppression 
     In some embodiments of the invention, inhibition of the expression of the nitrate uptake-associated polypeptide may be obtained by antisense suppression. For antisense suppression, the expression cassette is designed to express an RNA molecule complementary to all or part of a messenger RNA encoding the nitrate uptake-associated polypeptide. Over expression of the antisense RNA molecule can result in reduced expression of the native gene. Accordingly, multiple plant lines transformed with the antisense suppression expression cassette are screened to identify those that show the greatest inhibition of nitrate uptake-associated polypeptide expression. 
     The polynucleotide for use in antisense suppression may correspond to all or part of the complement of the sequence encoding the nitrate uptake-associated polypeptide, all or part of the complement of the 5′ and/or 3′ untranslated region of the nitrate uptake-associated transcript, or all or part of the complement of both the coding sequence and the untranslated regions of a transcript encoding the nitrate uptake-associated polypeptide. In addition, the antisense polynucleotide may be fully complementary (i.e., 100% identical to the complement of the target sequence) or partially complementary (i.e., less than 100% identical to the complement of the target sequence) to the target sequence. Antisense suppression may be used to inhibit the expression of multiple proteins in the same plant. See, for example, U.S. Pat. No. 5,942,657. Furthermore, portions of the antisense nucleotides may be used to disrupt the expression of the target gene. Generally, sequences of at least 50 nucleotides, 100 nucleotides, 200 nucleotides, 300, 400, 450, 500, 550, or greater may be used. Methods for using antisense suppression to inhibit the expression of endogenous genes in plants are described, for example, in Liu, et al., (2002)  Plant Physiol.  129:1732-1743 and U.S. Pat. Nos. 5,759,829 and 5,942,657, each of which is herein incorporated by reference. Efficiency of antisense suppression may be increased by including a poly-dT region in the expression cassette at a position 3′ to the antisense sequence and 5′ of the polyadenylation signal. See, U.S. Patent Publication No. 2002/0048814, herein incorporated by reference. 
     iii. Double-Stranded RNA Interference 
     In some embodiments of the invention, inhibition of the expression of a nitrate uptake-associated polypeptide may be obtained by double-stranded RNA (dsRNA) interference. For dsRNA interference, a sense RNA molecule like that described above for cosuppression and an antisense RNA molecule that is fully or partially complementary to the sense RNA molecule are expressed in the same cell, resulting in inhibition of the expression of the corresponding endogenous messenger RNA. 
     Expression of the sense and antisense molecules can be accomplished by designing the expression cassette to comprise both a sense sequence and an antisense sequence. Alternatively, separate expression cassettes may be used for the sense and antisense sequences. Multiple plant lines transformed with the dsRNA interference expression cassette or expression cassettes are then screened to identify plant lines that show the greatest inhibition of nitrate uptake-associated polypeptide expression. Methods for using dsRNA interference to inhibit the expression of endogenous plant genes are described in Waterhouse, et al., (1998)  Proc. Natl. Acad. Sci. USA  95:13959-13964, Liu, et al., (2002)  Plant Physiol.  129:1732-1743, and WO 99/49029, WO 99/53050, WO 99/61631, and WO 00/49035; each of which is herein incorporated by reference. 
     iv. Hairpin RNA Interference and Intron-Containing Hairpin RNA Interference 
     In some embodiments of the invention, inhibition of the expression of a nitrate uptake-associated polypeptide may be obtained by hairpin RNA (hpRNA) interference or intron-containing hairpin RNA (ihpRNA) interference. These methods are highly efficient at inhibiting the expression of endogenous genes. See, Waterhouse and Helliwell, (2003)  Nat. Rev. Genet.  4:29-38 and the references cited therein. 
     For hpRNA interference, the expression cassette is designed to express an RNA molecule that hybridizes with itself to form a hairpin structure that comprises a single-stranded loop region and a base-paired stem. The base-paired stem region comprises a sense sequence corresponding to all or part of the endogenous messenger RNA encoding the gene whose expression is to be inhibited, and an antisense sequence that is fully or partially complementary to the sense sequence. Alternatively, the base-paired stem region may correspond to a portion of a promoter sequence controlling expression of the gene to be inhibited. Thus, the base-paired stem region of the molecule generally determines the specificity of the RNA interference. hpRNA molecules are highly efficient at inhibiting the expression of endogenous genes, and the RNA interference they induce is inherited by subsequent generations of plants. See, for example, Chuang and Meyerowitz, (2000)  Proc. Natl. Acad. Sci. USA  97:4985-4990; Stoutjesdijk, et al., (2002)  Plant Physiol.  129:1723-1731; and Waterhouse and Helliwell, (2003)  Nat. Rev. Genet.  4:29-38. Methods for using hpRNA interference to inhibit or silence the expression of genes are described, for example, in Chuang and Meyerowitz, (2000)  Proc. Natl. Acad. Sci. USA  97:4985-4990; Stoutjesdijk, et al., (2002)  Plant Physiol.  129:1723-1731; Waterhouse and Helliwell, (2003)  Nat. Rev. Genet.  4:29-38; Pandolfini et al.,  BMC Biotechnology  3:7, and U.S. Patent Publication No. 2003/0175965; each of which is herein incorporated by reference. A transient assay for the efficiency of hpRNA constructs to silence gene expression in vivo has been described by Panstruga, et al., (2003)  Mol. Biol. Rep.  30:135-140, herein incorporated by reference. 
     For ihpRNA, the interfering molecules have the same general structure as for hpRNA, but the RNA molecule additionally comprises an intron that is capable of being spliced in the cell in which the ihpRNA is expressed. The use of an intron minimizes the size of the loop in the hairpin RNA molecule following splicing, and this increases the efficiency of interference. See, for example, Smith, et al., (2000)  Nature  407:319-320. In fact, Smith, et al., show 100% suppression of endogenous gene expression using ihpRNA-mediated interference. Methods for using ihpRNA interference to inhibit the expression of endogenous plant genes are described, for example, in Smith, et al., (2000)  Nature  407:319-320; Wesley, et al., (2001)  Plant J.  27:581-590; Wang and Waterhouse, (2001)  Curr. Opin. Plant Biol.  5:146-150; Waterhouse and Helliwell, (2003)  Nat. Rev. Genet.  4:29-38; Helliwell and Waterhouse, (2003)  Methods  30:289-295, and U.S. Patent Publication No. 2003/0180945, each of which is herein incorporated by reference. 
     The expression cassette for hpRNA interference may also be designed such that the sense sequence and the antisense sequence do not correspond to an endogenous RNA. In this embodiment, the sense and antisense sequence flank a loop sequence that comprises a nucleotide sequence corresponding to all or part of the endogenous messenger RNA of the target gene. Thus, it is the loop region that determines the specificity of the RNA interference. See, for example, WO 02/00904; Mette, et al., (2000)  EMBO J.  19:5194-5201; Matzke, et al., (2001)  Curr. Opin. Genet. Devel.  11:221-227; Scheid, et al., (2002)  Proc. Natl. Acad. Sci., USA  99:13659-13662; Aufsaftz, et al., (2002)  Proc. Natl. Acad. Sci.  99(4):16499-16506; Sijen, et al.,  Curr. Biol . (2001) 11:436-440), herein incorporated by reference. 
     v. Amplicon-Mediated Interference 
     Amplicon expression cassettes comprise a plant virus-derived sequence that contains all or part of the target gene but generally not all of the genes of the native virus. The viral sequences present in the transcription product of the expression cassette allow the transcription product to direct its own replication. The transcripts produced by the amplicon may be either sense or antisense relative to the target sequence (i.e., the messenger RNA for the nitrate uptake-associated polypeptide). Methods of using amplicons to inhibit the expression of endogenous plant genes are described, for example, in Angell and Baulcombe, (1997)  EMBO J.  16:3675-3684, Angell and Baulcombe, (1999)  Plant J.  20:357-362, and U.S. Pat. No. 6,646,805, each of which is herein incorporated by reference. 
     vi. Ribozymes 
     In some embodiments, the polynucleotide expressed by the expression cassette of the invention is catalytic RNA or has ribozyme activity specific for the messenger RNA of the nitrate uptake-associated polypeptide. Thus, the polynucleotide causes the degradation of the endogenous messenger RNA, resulting in reduced expression of the nitrate uptake-associated polypeptide. This method is described, for example, in U.S. Pat. No. 4,987,071, herein incorporated by reference. 
     vii. Small Interfering RNA or Micro RNA 
     In some embodiments of the invention, inhibition of the expression of a nitrate uptake-associated polypeptide may be obtained by RNA interference by expression of a gene encoding a micro RNA (miRNA). miRNAs are regulatory agents consisting of about 22 ribonucleotides. miRNA are highly efficient at inhibiting the expression of endogenous genes. See, for example Javier, et al., (2003)  Nature  425:257-263, herein incorporated by reference. 
     For miRNA interference, the expression cassette is designed to express an RNA molecule that is modeled on an endogenous miRNA gene. The miRNA gene encodes an RNA that forms a hairpin structure containing a 22-nucleotide sequence that is complementary to another endogenous gene (target sequence). For suppression of nitrate uptake-associated expression, the 22-nucleotide sequence is selected from a nitrate uptake-associated transcript sequence and contains 22 nucleotides of said nitrate uptake-associated sequence in sense orientation and 21 nucleotides of a corresponding antisense sequence that is complementary to the sense sequence. miRNA molecules are highly efficient at inhibiting the expression of endogenous genes, and the RNA interference they induce is inherited by subsequent generations of plants. 
     2. Polypeptide-Based Inhibition of Gene Expression 
     In one embodiment, the polynucleotide encodes a zinc finger protein that binds to a gene encoding a nitrate uptake-associated polypeptide, resulting in reduced expression of the gene. In particular embodiments, the zinc finger protein binds to a regulatory region of a nitrate uptake-associated gene. In other embodiments, the zinc finger protein binds to a messenger RNA encoding a nitrate uptake-associated polypeptide and prevents its translation. Methods of selecting sites for targeting by zinc finger proteins have been described, for example, in U.S. Pat. No. 6,453,242, and methods for using zinc finger proteins to inhibit the expression of genes in plants are described, for example, in U.S. Patent Publication No. 2003/0037355; each of which is herein incorporated by reference. 
     3. Polypeptide-Based Inhibition of Protein Activity 
     In some embodiments of the invention, the polynucleotide encodes an antibody that binds to at least one nitrate uptake-associated polypeptide, and reduces the enhanced nitrogen utilization activity of the nitrate uptake-associated polypeptide. In another embodiment, the binding of the antibody results in increased turnover of the antibody-nitrate uptake-associated complex by cellular quality control mechanisms. The expression of antibodies in plant cells and the inhibition of molecular pathways by expression and binding of antibodies to proteins in plant cells are well known in the art. See, for example, Conrad and Sonnewald, (2003)  Nature Biotech.  21:35-36, incorporated herein by reference. 
     4. Gene Disruption 
     In some embodiments of the present invention, the activity of a nitrate uptake-associated polypeptide is reduced or eliminated by disrupting the gene encoding the nitrate uptake-associated polypeptide. The gene encoding the nitrate uptake-associated polypeptide may be disrupted by any method known in the art. For example, in one embodiment, the gene is disrupted by transposon tagging. In another embodiment, the gene is disrupted by mutagenizing plants using random or targeted mutagenesis, and selecting for plants that have reduced nitrogen utilization activity. 
     i. Transposon Tagging 
     In one embodiment of the invention, transposon tagging is used to reduce or eliminate the nitrate uptake-associated activity of one or more nitrate uptake-associated polypeptide. Transposon tagging comprises inserting a transposon within an endogenous nitrate uptake-associated gene to reduce or eliminate expression of the nitrate uptake-associated polypeptide. “nitrate uptake-associated gene” is intended to mean the gene that encodes a nitrate uptake-associated polypeptide according to the invention. 
     In this embodiment, the expression of one or more nitrate uptake-associated polypeptide is reduced or eliminated by inserting a transposon within a regulatory region or coding region of the gene encoding the nitrate uptake-associated polypeptide. A transposon that is within an exon, intron, 5′ or 3′ untranslated sequence, a promoter, or any other regulatory sequence of a nitrate uptake-associated gene may be used to reduce or eliminate the expression and/or activity of the encoded nitrate uptake-associated polypeptide. 
     Methods for the transposon tagging of specific genes in plants are well known in the art. See, for example, Maes, et al., (1999)  Trends Plant Sci.  4:90-96; Dharmapuri and Sonti, (1999)  FEMS Microbiol. Lett.  179:53-59; Meissner, et al., (2000)  Plant J.  22:265-274; Phogat, et al., (2000)  J. Biosci.  25:57-63; Walbot, (2000)  Curr. Opin. Plant Biol.  2:103-107; Gai, et al., (2000)  Nucleic Acids Res.  28:94-96; Fitzmaurice, et al., (1999)  Genetics  153:1919-1928). In addition, the TUSC process for selecting Mu insertions in selected genes has been described in Bensen, et al., (1995)  Plant Cell  7:75-84; Mena, et al., (1996)  Science  274:1537-1540; and U.S. Pat. No. 5,962,764; each of which is herein incorporated by reference. 
     ii. Mutant Plants with Reduced Activity 
     Additional methods for decreasing or eliminating the expression of endogenous genes in plants are also known in the art and can be similarly applied to the instant invention. These methods include other forms of mutagenesis, such as ethyl methanesulfonate-induced mutagenesis, deletion mutagenesis, and fast neutron deletion mutagenesis used in a reverse genetics sense (with PCR) to identify plant lines in which the endogenous gene has been deleted. For examples of these methods see, Ohshima, et al., (1998)  Virology  243:472-481; Okubara, et al., (1994)  Genetics  137:867-874; and Quesada, et al., (2000)  Genetics  154:421-436; each of which is herein incorporated by reference. In addition, a fast and automatable method for screening for chemically induced mutations, TILLING (Targeting Induced Local Lesions In Genomes), using denaturing HPLC or selective endonuclease digestion of selected PCR products is also applicable to the instant invention. See, McCallum, et al., (2000)  Nat. Biotechnol.  18:455-457, herein incorporated by reference. 
     Mutations that impact gene expression or that interfere with the function (enhanced nitrogen utilization activity) of the encoded protein are well known in the art. Insertional mutations in gene exons usually result in null-mutants. Mutations in conserved residues are particularly effective in inhibiting the activity of the encoded protein. Conserved residues of plant nitrate uptake-associated polypeptides suitable for mutagenesis with the goal to eliminate nitrate uptake-associated activity have been described. Such mutants can be isolated according to well-known procedures, and mutations in different nitrate uptake-associated loci can be stacked by genetic crossing. See, for example, Gruis, et al., (2002)  Plant Cell  14:2863-2882. 
     In another embodiment of this invention, dominant mutants can be used to trigger RNA silencing due to gene inversion and recombination of a duplicated gene locus. See, for example, Kusaba, et al., (2003)  Plant Cell  15:1455-1467. 
     The invention encompasses additional methods for reducing or eliminating the activity of one or more nitrate uptake-associated polypeptide. Examples of other methods for altering or mutating a genomic nucleotide sequence in a plant are known in the art and include, but are not limited to, the use of RNA:DNA vectors, RNA:DNA mutational vectors, RNA:DNA repair vectors, mixed-duplex oligonucleotides, self-complementary RNA:DNA oligonucleotides, and recombinogenic oligonucleobases. Such vectors and methods of use are known in the art. See, for example, U.S. Pat. Nos. 5,565,350; 5,731,181; 5,756,325; 5,760,012; 5,795,972; and 5,871,984; each of which are herein incorporated by reference. See also, WO 98/49350, WO 99/07865, WO 99/25821, and Beetham, et al., (1999)  Proc. Natl. Acad. Sci. USA  96:8774-8778; each of which is herein incorporated by reference. 
     iii. Modulating Nitrogen Utilization Activity 
     In specific methods, the level and/or activity of a nitrate uptake-associated regulator in a plant is decreased by increasing the level or activity of the nitrate uptake-associated polypeptide in the plant. The increased expression of a negative regulatory molecule may decrease the level of expression of downstream one or more genes responsible for an improved nitrate uptake-associated phenotype. 
     Methods for increasing the level and/or activity of nitrate uptake-associated polypeptides in a plant are discussed elsewhere herein. 
     As discussed above, one of skill will recognize the appropriate promoter to use to modulate the level/activity of a nitrate uptake-associated in the plant. Exemplary promoters for this embodiment have been disclosed elsewhere herein. 
     In other embodiments, such plants have stably incorporated into their genome a nucleic acid molecule comprising a nitrate uptake-associated nucleotide sequence of the invention operably linked to a promoter that drives expression in the plant cell. 
     iv. Modulating Root Development 
     Methods for modulating root development in a plant are provided. By “modulating root development” is intended any alteration in the development of the plant root when compared to a control plant. Such alterations in root development include, but are not limited to, alterations in the growth rate of the primary root, the fresh root weight, the extent of lateral and adventitious root formation, the vasculature system, meristem development, or radial expansion. 
     Methods for modulating root development in a plant are provided. The methods comprise modulating the level and/or activity of the nitrate uptake-associated polypeptide in the plant. In one method, a nitrate uptake-associated sequence of the invention is provided to the plant. In another method, the nitrate uptake-associated nucleotide sequence is provided by introducing into the plant a polynucleotide comprising a nitrate uptake-associated nucleotide sequence of the invention, expressing the nitrate uptake-associated sequence, and thereby modifying root development. In still other methods, the nitrate uptake-associated nucleotide construct introduced into the plant is stably incorporated into the genome of the plant. 
     In other methods, root development is modulated by altering the level or activity of the nitrate uptake-associated polypeptide in the plant. A change in nitrate uptake-associated activity can result in at least one or more of the following alterations to root development, including, but not limited to, alterations in root biomass and length. 
     As used herein, “root growth” encompasses all aspects of growth of the different parts that make up the root system at different stages of its development in both monocotyledonous and dicotyledonous plants. It is to be understood that enhanced root growth can result from enhanced growth of one or more of its parts including the primary root, lateral roots, adventitious roots, etc. 
     Methods of measuring such developmental alterations in the root system are known in the art. See, for example, U.S. Application No. 2003/0074698 and Werner, et al., (2001)  PNAS  18:10487-10492, both of which are herein incorporated by reference. 
     As discussed above, one of skill will recognize the appropriate promoter to use to modulate root development in the plant. Exemplary promoters for this embodiment include constitutive promoters and root-preferred promoters. Exemplary root-preferred promoters have been disclosed elsewhere herein. 
     Stimulating root growth and increasing root mass by decreasing the activity and/or level of the nitrate uptake-associated polypeptide also finds use in improving the standability of a plant. The term “resistance to lodging” or “standability” refers to the ability of a plant to fix itself to the soil. For plants with an erect or semi-erect growth habit, this term also refers to the ability to maintain an upright position under adverse (environmental) conditions. This trait relates to the size, depth and morphology of the root system. In addition, stimulating root growth and increasing root mass by altering the level and/or activity of the nitrate uptake-associated polypeptide also finds use in promoting in vitro propagation of explants. 
     Furthermore, higher root biomass production due to nitrate uptake-associated activity has a direct effect on the yield and an indirect effect of production of compounds produced by root cells or transgenic root cells or cell cultures of said transgenic root cells. One example of an interesting compound produced in root cultures is shikonin, the yield of which can be advantageously enhanced by said methods. 
     Accordingly, the present invention further provides plants having modulated root development when compared to the root development of a control plant. In some embodiments, the plant of the invention has an increased level/activity of the nitrate uptake-associated polypeptide of the invention and has enhanced root growth and/or root biomass. In other embodiments, such plants have stably incorporated into their genome a nucleic acid molecule comprising a nitrate uptake-associated nucleotide sequence of the invention operably linked to a promoter that drives expression in the plant cell. 
     v. Modulating Shoot and Leaf Development 
     Methods are also provided for modulating shoot and leaf development in a plant. By “modulating shoot and/or leaf development” is intended any alteration in the to development of the plant shoot and/or leaf. Such alterations in shoot and/or leaf development include, but are not limited to, alterations in shoot meristem development, in leaf number, leaf size, leaf and stem vasculature, internode length, and leaf senescence. As used herein, “leaf development” and “shoot development” encompasses all aspects of growth of the different parts that make up the leaf system and the shoot system, respectively, at different stages of their development, both in monocotyledonous and dicotyledonous plants. Methods for measuring such developmental alterations in the shoot and leaf system are known in the art. See, for example, Werner, et al., (2001)  PNAS  98:10487-10492 and U.S. Publication No. 2003/0074698, each of which is herein incorporated by reference. 
     The method for modulating shoot and/or leaf development in a plant comprises modulating the activity and/or level of a nitrate uptake-associated polypeptide of the invention. In one embodiment, a nitrate uptake-associated sequence of the invention is provided. In other embodiments, the nitrate uptake-associated nucleotide sequence can be provided by introducing into the plant a polynucleotide comprising a nitrate uptake-associated nucleotide sequence of the invention, expressing the nitrate uptake-associated sequence, and thereby modifying shoot and/or leaf development. In other embodiments, the nitrate uptake-associated nucleotide construct introduced into the plant is stably incorporated into the genome of the plant. 
     In specific embodiments, shoot or leaf development is modulated by altering the level and/or activity of the nitrate uptake-associated polypeptide in the plant. A change in nitrate uptake-associated activity can result in at least one or more of the following alterations in shoot and/or leaf development, including, but not limited to, changes in leaf number, altered leaf surface, altered vasculature, internodes and plant growth, and alterations in leaf senescence, when compared to a control plant. 
     As discussed above, one of skill will recognize the appropriate promoter to use to modulate shoot and leaf development of the plant. Exemplary promoters for this embodiment include constitutive promoters, shoot-preferred promoters, shoot meristem-preferred promoters, and leaf-preferred promoters. Exemplary promoters have been disclosed elsewhere herein. 
     Increasing nitrate uptake-associated activity and/or level in a plant results in altered internodes and growth. Thus, the methods of the invention find use in producing modified plants. In addition, as discussed above, nitrate uptake-associated activity in the plant modulates both root and shoot growth. Thus, the present invention further provides methods for altering the root/shoot ratio. Shoot or leaf development can further be modulated by altering the level and/or activity of the nitrate uptake-associated polypeptide in the plant. 
     Accordingly, the present invention further provides plants having modulated shoot and/or leaf development when compared to a control plant. In some embodiments, the plant of the invention has an increased level/activity of the nitrate uptake-associated polypeptide of the invention. In other embodiments, the plant of the invention has a decreased level/activity of the nitrate uptake-associated polypeptide of the invention. 
     vi. Modulating Reproductive Tissue Development 
     Methods for modulating reproductive tissue development are provided. In one embodiment, methods are provided to modulate floral development in a plant. By “modulating floral development” is intended any alteration in a structure of a plant&#39;s reproductive tissue as compared to a control plant in which the activity or level of the nitrate uptake-associated polypeptide has not been modulated. “Modulating floral development” further includes any alteration in the timing of the development of a plant&#39;s reproductive tissue (i.e., a delayed or an accelerated timing of floral development) when compared to a control plant in which the activity or level of the nitrate uptake-associated polypeptide has not been modulated. Macroscopic alterations may include changes in size, shape, number, or location of reproductive organs, the developmental time period that these structures form, or the ability to maintain or proceed through the flowering process in times of environmental stress. Microscopic alterations may include changes to the types or shapes of cells that make up the reproductive organs. 
     The method for modulating floral development in a plant comprises modulating nitrate uptake-associated activity in a plant. In one method, a nitrate uptake-associated sequence of the invention is provided. A nitrate uptake-associated nucleotide sequence can be provided by introducing into the plant a polynucleotide comprising a nitrate uptake-associated nucleotide sequence of the invention, expressing the nitrate uptake-associated sequence, and thereby modifying floral development. In other embodiments, the nitrate uptake-associated nucleotide construct introduced into the plant is stably incorporated into the genome of the plant. 
     In specific methods, floral development is modulated by increasing the level or activity of the nitrate uptake-associated polypeptide in the plant. A change in nitrate uptake-associated activity can result in at least one or more of the following alterations in floral development, including, but not limited to, altered flowering, changed number of flowers, modified male sterility, and altered seed set, when compared to a control plant. Inducing delayed flowering or inhibiting flowering can be used to enhance yield in forage crops such as alfalfa. Methods for measuring such developmental alterations in floral development are known in the art. See, for example, Mouradov, et al., (2002)  The Plant Cell S 111-S130, herein incorporated by reference. 
     As discussed above, one of skill will recognize the appropriate promoter to use to modulate floral development of the plant. Exemplary promoters for this embodiment include constitutive promoters, inducible promoters, shoot-preferred promoters, and inflorescence-preferred promoters. 
     In other methods, floral development is modulated by altering the level and/or activity of the nitrate uptake-associated sequence of the invention. Such methods can comprise introducing a nitrate uptake-associated nucleotide sequence into the plant and changing the activity of the nitrate uptake-associated polypeptide. In other methods, the nitrate uptake-associated nucleotide construct introduced into the plant is stably incorporated into the genome of the plant. Altering expression of the nitrate uptake-associated sequence of the invention can modulate floral development during periods of stress. Such methods are described elsewhere herein. Accordingly, the present invention further provides plants having modulated floral development when compared to the floral development of a control plant. Compositions include plants having an altered level/activity of the nitrate uptake-associated polypeptide of the invention and having an altered floral development. Compositions also include plants having a modified level/activity of the nitrate uptake-associated polypeptide of the invention wherein the plant maintains or proceeds through the flowering process in times of stress. 
     Methods are also provided for the use of the nitrate uptake-associated sequences of the invention to increase seed size and/or weight. The method comprises increasing the activity of the nitrate uptake-associated sequences in a plant or plant part, such as the seed. An increase in seed size and/or weight comprises an increased size or weight of the seed and/or an increase in the size or weight of one or more seed part including, for example, the embryo, endosperm, seed coat, aleurone, or cotyledon. 
     As discussed above, one of skill will recognize the appropriate promoter to use to increase seed size and/or seed weight. Exemplary promoters of this embodiment include constitutive promoters, inducible promoters, seed-preferred promoters, embryo-preferred promoters, and endosperm-preferred promoters. 
     The method for altering seed size and/or seed weight in a plant comprises increasing nitrate uptake-associated activity in the plant. In one embodiment, the nitrate uptake-associated nucleotide sequence can be provided by introducing into the plant a polynucleotide comprising a nitrate uptake-associated nucleotide sequence of the invention, expressing the nitrate uptake-associated sequence, and thereby increasing seed weight and/or size. In other embodiments, the nitrate uptake-associated nucleotide construct introduced into the plant is stably incorporated into the genome of the plant. 
     It is further recognized that increasing seed size and/or weight can also be accompanied by an increase in the speed of growth of seedlings or an increase in early vigor. As used herein, the term “early vigor” refers to the ability of a plant to grow rapidly during early development, and relates to the successful establishment, after germination, of a well-developed root system and a well-developed photosynthetic apparatus. In addition, an increase in seed size and/or weight can also result in an increase in plant yield when compared to a control. 
     Accordingly, the present invention further provides plants having an increased seed weight and/or seed size when compared to a control plant. In other embodiments, plants having an increased vigor and plant yield are also provided. In some embodiments, the plant of the invention has a modified level/activity of the nitrate uptake-associated polypeptide of the invention and has an increased seed weight and/or seed size. In other embodiments, such plants have stably incorporated into their genome a nucleic acid molecule comprising a nitrate uptake-associated nucleotide sequence of the invention operably linked to a promoter that drives expression in the plant cell. 
     vii. Method of Use for Nitrate Uptake-Associated Polynucleotide, Expression Cassettes, and Additional Polynucleotides 
     The nucleotides, expression cassettes and methods disclosed herein are useful in regulating expression of any heterologous nucleotide sequence in a host plant in order to vary the phenotype of a plant. Various changes in phenotype are of interest including modifying the fatty acid composition in a plant, altering the amino acid content of a plant, altering a plant&#39;s pathogen defense mechanism, and the like. These results can be achieved by providing expression of heterologous products or increased expression of endogenous products in plants. Alternatively, the results can be achieved by providing for a reduction of expression of one or more endogenous products, particularly enzymes or cofactors in the plant. These changes result in a change in phenotype of the transformed plant. 
     Genes of interest are reflective of the commercial markets and interests of those involved in the development of the crop. Crops and markets of interest change, and as developing nations open up world markets, new crops and technologies will emerge also. In addition, as our understanding of agronomic traits and characteristics such as yield and heterosis increase, the choice of genes for transformation will change accordingly. General categories of genes of interest include, for example, those genes involved in information, such as zinc fingers, those involved in communication, such as kinases, and those involved in housekeeping, such as heat shock proteins. More specific categories of transgenes, for example, include genes encoding important traits for agronomics, insect resistance, disease resistance, herbicide resistance, sterility, grain characteristics, and commercial products. Genes of interest include, generally, those involved in oil, starch, carbohydrate, or nutrient metabolism as well as those affecting kernel size, sucrose loading, and the like. 
     In certain embodiments the nucleic acid sequences of the present invention can be used in combination (“stacked”) with other polynucleotide sequences of interest in order to create plants with a desired phenotype. The combinations generated can include multiple copies of any one or more of the polynucleotides of interest. The polynucleotides of the present invention may be stacked with any gene or combination of genes to produce plants with a variety of desired trait combinations, including but not limited to traits desirable for animal feed such as high oil genes (e.g., U.S. Pat. No. 6,232,529); balanced amino acids (e.g., hordothionins (U.S. Pat. Nos. 5,990,389; 5,885,801; 5,885,802; and 5,703,409); barley high lysine (Williamson, et al., (1987)  Eur. J. Biochem.  165:99-106; and WO 98/20122); and high methionine proteins (Pedersen, et al., (1986)  J. Biol. Chem.  261:6279; Kirihara, et al., (1988)  Gene  71:359; and Musumura, et al., (1989)  Plant Mol. Biol.  12:123)); increased digestibility (e.g., modified storage proteins (U.S. application Ser. No. 10/053,410, filed Nov. 7, 2001); and thioredoxins (U.S. application Ser. No. 10/005,429, filed Dec. 3, 2001)), the disclosures of which are herein incorporated by reference. The polynucleotides of the present invention can also be stacked with traits desirable for insect, disease or herbicide resistance (e.g.,  Bacillus thuringiensis  toxic proteins (U.S. Pat. Nos. 5,366,892; 5,747,450; 5,737,514; 5723,756; 5,593,881; Geiser, et al., (1986)  Gene  48:109); lectins (Van Damme, et al., (1994)  Plant Mol. Biol.  24:825); fumonisin detoxification genes (U.S. Pat. No. 5,792,931); avirulence and disease resistance genes (Jones, et al., (1994)  Science  266:789; Martin, et al., (1993)  Science  262:1432; Mindrinos, et al., (1994)  Cell  78:1089); acetolactate synthase (ALS) mutants that lead to herbicide resistance such as the S4 and/or Hra mutations; inhibitors of glutamine synthase such as phosphinothricin or basta (e.g., bar gene); and glyphosate resistance (EPSPS gene)); and traits desirable for processing or process products such as high oil (e.g., U.S. Pat. No. 6,232,529); modified oils (e.g., fatty acid desaturase genes (U.S. Pat. No. 5,952,544; WO 94/11516)); modified starches (e.g., ADPG pyrophosphorylases (AGPase), starch synthases (SS), starch branching enzymes (SBE) and starch debranching enzymes (SDBE)); and polymers or bioplastics (e.g., U.S. Pat. No. 5,602,321; beta-ketothiolase, polyhydroxybutyrate synthase, and acetoacetyl-CoA reductase (Schubert, et al., (1988)  J. Bacteriol.  170:5837-5847) facilitate expression of polyhydroxyalkanoates (PHAs)), the disclosures of which are herein incorporated by reference. One could also combine the polynucleotides of the present invention with polynucleotides affecting agronomic traits such as male sterility (e.g., see U.S. Pat. No. 5,583,210), stalk strength, flowering time, or transformation technology traits such as cell cycle regulation or gene targeting (e.g., WO 99/61619; WO 00/17364; WO 99/25821), the disclosures of which are herein incorporated by reference. 
     In one embodiment, sequences of interest improve plant growth and/or crop yields. For example, sequences of interest include agronomically important genes that result in improved primary or lateral root systems. Such genes include, but are not limited to, nutrient/water transporters and growth induces. Examples of such genes, include but are not limited to, maize plasma membrane H + -ATPase (MHA2) (Frias, et al., (1996)  Plant Cell  8:1533-44); AKT1, a component of the potassium uptake apparatus in  Arabidopsis , (Spalding, et al., (1999)  J Gen Physiol  113:909-18); RML genes which activate cell division cycle in the root apical cells (Cheng, et al., (1995)  Plant Physiol  108:881); maize glutamine synthetase genes (Sukanya, et al., (1994)  Plant Mol Biol  26:1935-46) and hemoglobin (Duff, et al., (1997)  J. Biol. Chem  27:16749-16752, Arredondo-Peter, et al., (1997)  Plant Physiol.  115:1259-1266; Arredondo-Peter, et al., (1997)  Plant Physiol  114:493-500 and references sited therein). The sequence of interest may also be useful in expressing antisense nucleotide sequences of genes that that negatively affects root development. 
     Additional, agronomically important traits such as oil, starch, and protein content can be genetically altered in addition to using traditional breeding methods. Modifications include increasing content of oleic acid, saturated and unsaturated oils, increasing levels of lysine and sulfur, providing essential amino acids, and also modification of starch. Hordothionin protein modifications are described in U.S. Pat. Nos. 5,703,049, 5,885,801, 5,885,802, and 5,990,389, herein incorporated by reference. Another example is lysine and/or sulfur rich seed protein encoded by the soybean 2S albumin described in U.S. Pat. No. 5,850,016, and the chymotrypsin inhibitor from barley, described in Williamson, et al., (1987)  Eur. J. Biochem.  165:99-106, the disclosures of which are herein incorporated by reference. 
     Derivatives of the coding sequences can be made by site-directed mutagenesis to increase the level of preselected amino acids in the encoded polypeptide. For example, the gene encoding the barley high lysine polypeptide (BHL) is derived from barley chymotrypsin inhibitor, U.S. application Ser. No. 08/740,682, filed Nov. 1, 1996, and WO 98/20133, the disclosures of which are herein incorporated by reference. Other proteins include methionine-rich plant proteins such as from sunflower seed (Lilley, et al., (1989)  Proceedings of the World Congress on Vegetable Protein Utilization in Human Foods and Animal Feedstuffs , ed. Applewhite (American Oil Chemists Society, Champaign, Ill.), pp. 497-502; herein incorporated by reference); corn (Pedersen, et al., (1986)  J. Biol. Chem.  261:6279; Kirihara, et al., (1988)  Gene  71:359; both of which are herein incorporated by reference); and rice (Musumura, et al., (1989)  Plant Mol. Biol.  12:123, herein incorporated by reference). Other agronomically important genes encode latex, Floury 2, growth factors, seed storage factors, and transcription factors. 
     Insect resistance genes may encode resistance to pests that have great yield drag such as rootworm, cutworm, European Corn Borer, and the like. Such genes include, for example,  Bacillus thuringiensis  toxic protein genes (U.S. Pat. Nos. 5,366,892; 5,747,450; 5,736,514; 5,723,756; 5,593,881; and Geiser, et al., (1986)  Gene  48:109); and the like. 
     Genes encoding disease resistance traits include detoxification genes, such as against fumonosin (U.S. Pat. No. 5,792,931); avirulence (avr) and disease resistance (R) genes (Jones, et al., (1994)  Science  266:789; Martin, et al., (1993)  Science  262:1432; and Mindrinos, et al., (1994)  Cell  78:1089); and the like. 
     Herbicide resistance traits may include genes coding for resistance to herbicides that act to inhibit the action of acetolactate synthase (ALS), in particular the sulfonylurea-type herbicides (e.g., the acetolactate synthase (ALS) gene containing mutations leading to such resistance, in particular the S4 and/or Hra mutations), genes coding for resistance to herbicides that act to inhibit action of glutamine synthase, such as phosphinothricin or basta (e.g., the bar gene), or other such genes known in the art. The bar gene encodes resistance to the herbicide basta, the nptII gene encodes resistance to the antibiotics kanamycin and geneticin, and the ALS-gene mutants encode resistance to the herbicide chlorsulfuron. 
     Sterility genes can also be encoded in an expression cassette and provide an alternative to physical detasseling. Examples of genes used in such ways include male tissue-preferred genes and genes with male sterility phenotypes such as QM, described in U.S. Pat. No. 5,583,210. Other genes include kinases and those encoding compounds toxic to either male or female gametophytic development. 
     The quality of grain is reflected in traits such as levels and types of oils, saturated and unsaturated, quality and quantity of essential amino acids, and levels of cellulose. In corn, modified hordothionin proteins are described in U.S. Pat. Nos. 5,703,049, 5,885,801, 5,885,802, and 5,990,389. 
     Commercial traits can also be encoded on a gene or genes that could increase for example, starch for ethanol production, or provide expression of proteins. Another important commercial use of transformed plants is the production of polymers and bioplastics such as described in U.S. Pat. No. 5,602,321. Genes such as β-Ketothiolase, PHBase (polyhydroxyburyrate synthase), and acetoacetyl-CoA reductase (see, Schubert, et al., (1988)  J. Bacteria  170:5837-5847) facilitate expression of polyhyroxyalkanoates (PHAs). 
     Exogenous products include plant enzymes and products as well as those from other sources including procaryotes and other eukaryotes. Such products include enzymes, cofactors, hormones, and the like. The level of proteins, particularly modified proteins having improved amino acid distribution to improve the nutrient value of the plant, can be increased. This is achieved by the expression of such proteins having enhanced amino acid content. 
     This invention can be better understood by reference to the following non-limiting examples. It will be appreciated by those skilled in the art that other embodiments of the invention may be practiced without departing from the spirit and the scope of the invention as herein disclosed and claimed. 
     EXAMPLES 
     Example 1 
     Creation of an  Arabidopsis  Population 
     A T-DNA based binary construct was created, containing four multimerized enhancer elements derived from the Cauliflower Mosaic Virus 35S promoter, corresponding to sequences −341 to −64, as defined by Odell et al. (1985)  Nature  313:810-812. The construct also contains vector sequences (pUC9) to allow plasmid rescue, transposon sequences (Ds) to remobilize the T-DNA, and the bar gene to allow for glufosinate selection of transgenic plants. Only the 10.8 kb segment from the right border (RB) to left border (LB) inclusive will be transferred into the host plant genome. Since the enhancer elements are located near the RB, they can induce cis-activation of genomic loci following T-DNA integration. 
     The resulting construct was transformed into  Agrobacterium tumefaciens  strain C58, grown in LB at 25° C. to OD600 ˜1.0. Cells were then pelleted by centrifugation and resuspended in an equal volume of 5% sucrose/0.05% Silwet L-77 (OSI Specialties, Inc). At early bolting, soil grown  Arabidopsis thaliana  ecotype Col-0 were top watered with the  Agrobacterium  suspension. A week later, the same plants were top watered again with the same  Agrobacterium  strain in sucrose/Silwet. The plants were then allowed to set seed as normal. The resulting T 1  seed were sown on soil, and transgenic seedlings were selected by spraying with glufosinate (Finale®; AgrEvo; Bayer Environmental Science). T 2  seed was collected from approximately 35,000 individual glufosinate resistant T 1  plants. T 2  plants were grown and equal volumes of T 3  seed from 96 separate T 2  lines were pooled. This constituted 360 sub-populations. 
     A total of 100,000 glufosinate resistant T 1  seedlings were selected. T 2  seeds from each line were kept separate. 
     Example 2 
     Screens to Identify Lines with Altered Root Architecture 
     Activation-tagged  Arabidopsis  seedlings, grown under non-limiting nitrogen conditions, were analyzed for altered root system architecture when compared to control seedlings during early development from the population described in Example 1. 
     Validated leads from in-house screen were subjected to a vertical plate assay to evaluate enhanced root growth. The results were validated using WinRHIZO® as described below. T2 seeds were sterilized using 50% household bleach 0.01% triton X-100 solution and plated on petri plates containing the following medium: 0.5×N-Free Hoagland&#39;s, 60 mM KNO 3 , 0.1% sucrose, 1 mM MES and 1% Phytagel™ at a density of 4 seeds/plate. Plates were kept for three days at 4° C. to stratify seeds and then held vertically for 11 days at 22° C. light and 20° C. dark. Photoperiod was 16 h; 8 h dark and average light intensity was ˜160 μmol/m 2 /s. Plates were placed vertically into the eight center positions of a 10 plate rack with the first and last position holding blank plates. The racks and the plates within a rack were rotated every other day. Two sets of pictures were taken for each plate. The first set taking place at day 14-16 when the primary roots for most lines had reached the bottom of the plate, the second set of pictures two days later after more lateral roots had developed. The latter set of picture was usually used for data analysis. These seedlings grown on vertical plates were analyzed for root growth with the software WinRHIZO® (Regent Instruments Inc), an image analysis system specifically designed for root measurement. WinRHIZO® uses the contrast in pixels to distinguish the light root from the darker background. To identify the maximum amount of roots without picking up background, the pixel classification was 150-170 and the filter feature was used to remove objects that have a length/width ratio less then 10.0. The area on the plates analyzed was from the edge of the plant&#39;s leaves to about 1 cm from the bottom of the plate. The exact same WinRHIZO® settings and area of analysis were used to analyze all plates within a batch. The total root length score given by WinRHIZO® for a plate was divided by the number of plants that had germinated and had grown halfway down the plate. Eight plates for every line were grown and their scores were averaged. This average was then compared to the average of eight plates containing wild type seeds that were grown at the same time. 
     Lines with enhanced root growth characteristics were expected to lie at the upper extreme of the root area distributions. A sliding window approach was used to estimate the variance in root area for a given rack with the assumption that there could be up to two outliers in the rack. Environmental variations in various factors including growth media, temperature, and humidity can cause significant variation in root growth, especially between sow dates. Therefore the lines were grouped by sow date and shelf for the data analysis. The racks in a particular sow date/shelf group were then sorted by mean root area. Root area distributions for sliding windows were performed by combining data for a rack, r i , with data from the rack with the next lowest, (r i−1 , and the next highest mean root area, r i+1 . The variance of the combined distribution was then analyzed to identify outliers in r i  using a Grubbs-type approach (Barnett et al., Outliers in Statistical Data, John Wiley &amp; Sons, 3 rd  edition (1994). 
     Example 3 
     pH Indicator Dye Assay to Identify Genes Involved in Nitrate Uptake 
     Analysis was performed using the following pH indicator dye assay to identify the genes involved with nitrate uptake as detailed in U.S. patent application Ser. No. 12/166,473, filed Jul. 3, 2007. Using the protocol detailed in U.S. patent application Ser. No. 12/166,473, filed Jul. 3, 2007,  Arabidopsis  lines overexpressing At1g67330 with the CaMV 35S promoter or tubulin promoter had significantly less (p&lt;0.05) nitrate remaining in the medium than wild-type controls.  Arabidopsis  lines overexpressing maize pco639489 with the maize ubiquitin promoter had significantly less (p&lt;0.05) nitrate remaining in the medium than wild-type controls. 
     Example 4 
     Screen of Candidate Genes Under Nitrogen Limiting Conditions 
     Transgenic seed selected by the presence of the fluorescent marker YFP can also be screened for their tolerance to grow under nitrogen limiting conditions. Transgenic individuals expressing the  Arabidopsis  Candidate gene are plated on Low N medium (0.5×N-Free Hoagland&#39;s, 0.4 mM potassium nitrate, 0.1% sucrose, 1 mM MES and 0.25% Phytagel™), such that 32 transgenic individuals are grown next to 32 wild-type individuals on one plate. Plants are evaluated at 10, 11, 12 and 13 days. If a line shows a statistically significant difference from the controls, the line is considered a validated nitrogen-deficiency tolerant line. After masking the plate image to remove background color, two different measurements are collected for each individual: total rosetta area, and the percentage of color that falls into a green color bin. Using hue, saturation and intensity data (HIS), the green color bin consists of hues 50-66. Total rosetta area is used as a measure of plant biomass, whereas the green color bin has been shown by dose-response studies to be an indicator of nitrogen assimilation. 
     Example 5 
     Identification of Activation-Tagged Genes 
     Genes flanking the T-DNA insert in lines with improved nitrate uptake are identified using one, or both, of the following two standard procedures: (1) thermal asymmetric interlaced (TAIL) PCR (Liu et al., (1995),  Plant J.  8:457-63); and (2) SAIFF PCR (Siebert et al., (1995)  Nucleic Acids Res.  23:1087-1088). In lines with complex multimerized T-DNA inserts, TAIL PCR and SAIFF PCR may both prove insufficient to identify candidate genes. In these cases, other procedures, including inverse PCR, plasmid rescue and/or genomic library construction, can be employed. 
     A successful result is one where a single TAIL or SAIFF PCR fragment contains a T-DNA border sequence and  Arabidopsis  genomic sequence. 
     Once a tag of genomic sequence flanking a T-DNA insert is obtained, candidate genes are identified by alignment to publicly available  Arabidopsis  genome sequence. 
     Specifically, the annotated gene nearest the 35S enhancer elements/T-DNA RB are candidates for genes that are activated. 
     To verify that an identified gene is truly near a T-DNA and to rule out the possibility that the TAIL/SAIFF fragment is a chimeric cloning artifact, a diagnostic PCR on genomic DNA is done with one oligo in the T-DNA and one oligo specific for the candidate gene. Genomic DNA samples that give a PCR product are interpreted as representing a T-DNA insertion. This analysis also verifies a situation in which more than one insertion event occurs in the same line, e.g., if multiple differing genomic fragments are identified in TAIL and/or SAIFF PCR analyses. 
     Example 6 
     Validation of a Candidate Gene for its Ability to Enhance Nitrate Uptake in Plants Via Transformation into  Arabidopsis    
     Candidate genes can be transformed into  Arabidopsis  and overexpressed under a promoter such as 35S or maize Ubiquitin promoters. If the same or similar phenotype is observed in the transgenic line as in the parent activation-tagged line, then the candidate gene is considered to be a validated “lead gene” in  Arabidopsis . The  Arabidopsis  AT1G67330 gene can be directly tested for its ability to enhance nitrate uptake in  Arabidopsis.    
     A 35S-AT1G67330 gene construct was introduced into wild-type  Arabidopsis  ecotype Col-0, using the standard  Agrobacterium -mediated transformation procedures. 
     Transgenic T2 seeds from multiple independent T1 lines may be selected by the presence of the fluorescent YFP marker. Fluorescent seeds were subjected to the pH and nitrate uptake assays following the procedures described herein. Transgenic T2 seeds were re-screened using 3 or 4 plates per construct. Each plate contained non-transformed Columbia seed discarded from fluorescent seed sorting to serve as a control. 
     Example 7 
     NUE Assay Plant Growth 
     Seeds of  Arabidopsis thaliana  (control and transgenic line), ecotype Columbia, were surface sterilized (Sanchez et al., 2002) and then plated on to Murashige and Skoog (MS) medium containing 0.8% (w/v) Bacto-Agar (Difco). Plates were incubated for 3 days in darkness at 4° C. to break dormancy (stratification) and transferred thereafter to growth chambers (Conviron, Manitoba, Canada) at a temperature of 20° C. under a 16-h light/8-h dark cycle. The average light intensity was 120 μE/m2/s. Seedling were grown for 12 days and then transfer to soil based pots. Potted plants were grown on a nutrient-free soil SunGro® LB2 Metro-Mix 200 (Scott&#39;s Sierra Horticultural Products, Marysville, Ohio, USA) in individual 1.5-in pots (Arabidopsis system; Lehle Seeds, Round Rock, Tex., USA) in growth chambers, as described above. Plants were watered with 0.6 or 6.5 mM potassium nitrate in the nutrient solution based on Murashige and Skoog (MS free Nitrogen) medium. The relative humidity was maintained around 70%. 16-18 days later plant shoots were collected for evaluation of biomass and SPAD readings. Plants that improve NUE may have increased biomass at either high or low nitrate concentrations. 
     Example 8 
     Sucrose Growth Assay 
     The Columbia line of  Arabidopsis thaliana  was obtained from the  Arabidopsis  Biological Resource Center (Columbus, Ohio). For early analysis (Columbia and T3 transgenic lines), seeds were surface-sterilized with 70% ethanol followed by 40% Clorox® and rinsed with sterile deionized water. Surface-sterilized seed were sown onto square Petri plates (25 cm) containing 95 mL of sterile medium consisting of 0.5× Murashige and Skoog (1962) salts (Life Technologies) and 4% (w/v) phytagel (Sigma). The medium contained no supplemental sucrose. Sucrose was added to medium in 0.1%, 0.5% and 1.5% concentration. Plates were arranged vertically in plastic racks and placed in a cold room for 3 days at 4° C. to synchronize germination. Racks with cold stratified seed were then transferred into growth chambers (Conviron, Manitoba, Canada) with day and night temperatures of 22 and 20° C., respectively. The average light intensity at the level of the rosette was maintained at 110 mol/m2/sec1 during a 16-hr light cycle development beginning at removal from the cold room (day 3 after sowing) until the seedlings were harvested on day 14. Images were taken and total fresh weight of root and shoot were measured. Two experiments will be performed. If overexpression of At2g36295 alters the carbon and nitrogen balance, then data may show that the At2g36295 overexpression transgenic plants had increased or decreased root biomass and/or leaf biomass at different sucrose concentrations when compared to wild-type  Arabidopsis.    
     Example 9 
     NUE Seeding Assay Protocol 
     Seed of transgenic events are separated into transgene (heterozygous) and null seed using a seed color marker. Two different random assignments of treatments were made to each block of 54 pots arranged 6 rows of 9 columns using 9 replicates of all treatments. In one case null seed of 5 events of the same construct were mixed and used as control for comparison of the 5 positive events in this block making up 6 treatment combinations in each block. In the second case, 3 transgenic positive treatments and their corresponding nulls were randomly assigned to the 54 pots of the block, making 6 treatment combinations for each block, containing 9 replicates of all treatment combinations. In the first case transgenic parameters were compared to a bulked construct null and in the second case transgenic parameters were compared to the corresponding event null. In cases where there were 10, 15 or 20 events in a construct the events were assigned in groups of 5 events, the variances calculated for each block of 54 pots but the block null means pooled across blocks before mean comparisons were made. 
     Two seed of each treatment were planted in 4 inch, square pots containing TURFACE®-MVP on 8 inch, staggered centers and watered four times each day with a solution containing the following nutrients: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 1 mM CaCl2 
                 2 mM MgSO4 
                 0.5 mM KH2PO4 
                  83 ppm Sprint330 
               
               
                 3 mM KCl 
                 1 mM KNO3 
                   1 uM ZnSO4 
                   1 uM MnCl2 
               
               
                 3 uM H3BO4 
                 1 uM MnCl2 
                 0.1 uM CuSO4 
                 0.1 uM NaMoO4 
               
               
                   
               
            
           
         
       
     
     After emergence the plants are thinned to one seed per pot. Treatments routinely are planted on a Monday, emerge the following Friday and are harvested 18 days after planting. At harvest, plants are removed from the pots and the Turface washed from the roots. The roots are separated from the shoot, placed in a paper bag and dried at 70° C. for 70 hr. The dried plant parts (roots and shoots) are weighed and placed in a 50 ml conical tube with approximately 20 5/32 inch steel balls and ground by shaking in a paint shaker. Approximately, 30 mg of the ground tissue (weight recorded for later adjustment) is hydrolyzed in 2 ml of 20% H 2 O 2  and 6M H 2 SO 4  for 30 min at 170° C. After cooling, water is added to 20 ml, mixed thoroughly, and a 50 μl aliquot removed and added to 950 μl 1M Na 2 CO 3 . The ammonia in this solution is used to estimate total reduced plant nitrogen by placing 100 μl of this solution in individual wells of a 96 well plate followed by adding 50 μl of OPA solution. Fluorescence, excitation=360 nM/emission=530 nM, is determined and compared to NH 4 Cl standards dissolved in a similar solution and treated with OPA solution. 
       OPA solution−5 ul Mercaptoethanol+1 ml OPA stock solution(make fresh, daily)OPA stock−50 mg o-phthadialdehyde(OPA-Sigma #P0657)dissolved in 1.5 ml methanol+4.4 ml 1M Borate buffer pH9.5(3.09 g H 3 BO 4 +1 g NaOH in 50 ml water)+0.55 ml 20% SDS(make fresh weekly) 
     Using these data the following parameters were measured and means compared to 
     Total Plant Biomass 
     Root Biomass 
     Shoot Biomass 
     Root/Shoot Ratio 
     Plant N concentration 
     Total Plant N 
     Variance is calculated within each block using a nearest neighbor calculation as well as by Analysis of Variance (ANOV) using a completely random design (CRD) model. An overall treatment effect for each block is calculated using an F statistic by dividing overall block treatment mean square by the overall block error mean square. 
     When the maize homolog of At2g36295 (SEQ ID NO:8) is overexpressed in maize, a validated lead will show a significant improvement in root and shoot biomass and/or a significant increase in plant N concentration in this hybrid seedling assay at 1 mM KNO 3 . 
     Example 10 
     Inter-Relationship of Related Proteins 
       FIG. 1  is a dendrogram of the ClustalW results for At1g67330 and related proteins. At1g67330 forms a cluster with a number of other  Arabidopsis  and dicot species.  FIG. 2  shows the sequence alignment of At1 g67330 and related proteins including a consensus sequence. The Rice Os11g29780.1,  Sorghum  Sb05g106480, and Maize PCO639489 form an apparent monocot ortholog grouping. This grouping represents a single-gene-from-each-species At1 g67330-ortholog set from monocots. Many of the other dicot species, whether  Brassica  (Bs),  Vitis vinifera  (Vv), or  Populus trichocarpa  (Pt), exhibit two members in this subcluster containing At1g67330. 
     Example 11 
     Composition of cDNA Libraries: Isolation and Sequencing of cDNA Clones 
     cDNA libraries representing mRNAs from various tissues of  Canna edulis  (Canna),  Momordica charantia  (balsam pear),  Brassica  (mustard),  Cyamopsis tetragonoloba  (guar),  Zea mays  (maize),  Oryza sativa  (rice),  Glycine max  (soybean),  Helianthus annuus  (sunflower) and  Triticum aestivum  (wheat) were prepared. cDNA libraries may be prepared by any one of many methods available. For example, the cDNAs may be introduced into plasmid vectors by first preparing the cDNA libraries in Uni-ZAP™ XR vectors according to the manufacturer&#39;s protocol (Stratagene Cloning Systems, La Jolla, Calif.). 
     Full-insert sequence (FIS) data is generated utilizing a modified transposition protocol. Clones identified for FIS are recovered from archived glycerol stocks as single colonies, and plasmid DNAs are isolated via alkaline lysis. Isolated DNA templates are reacted with vector primed M13 forward and reverse oligonucleotides in a PCR-based sequencing reaction and loaded onto automated sequencers. Confirmation of clone identification is performed by sequence alignment to the original EST sequence from which the FIS request is made. 
     Confirmed templates are transposed via the Primer Island transposition kit (PE Applied Biosystems, Foster City, Calif.) which is based upon the  Saccharomyces cerevisiae  Ty1 transposable element (Devine and Boeke (1994)  Nucleic Acids Res.  22:3765-3772). The in vitro transposition system places unique binding sites randomly throughout a population of large DNA molecules. Multiple subclones are randomly selected from each transposition reaction, plasmid DNAs are prepared via alkaline lysis, and templates are sequenced (ABI Prism dye-terminator ReadyReaction mix) outward from the transposition event site, utilizing unique primers specific to the binding sites within the transposon. 
     Sequence data is collected (ABI Prism Collections) and assembled using Phred and Phrap (Ewing et al. (1998)  Genome Res.  8:175-185; Ewing and Green (1998)  Genome Res.  8:186-194 The resulting DNA fragment is ligated into a pBluescript vector using a commercial kit and following the manufacturer&#39;s protocol. This kit is selected from many available from several vendors including Invitrogen™ (Carlsbad, Calif.), Promega Biotech (Madison, Wis.), and Gibco-BRL (Gaithersburg, Md.). The plasmid DNA is isolated by alkaline lysis method and submitted for sequencing and assembly using Phred/Phrap, as above. 
     Example 12 
     Identification of cDNA Clones 
     cDNA clones encoding nitrate uptake-associated-like polypeptides were identified by conducting BLAST (Basic Local Alignment Search Tool; Altschul et al. (1993)  J. Mol. Biol.  215:403-410; see also the explanation of the BLAST algorithm on the world wide web site for the National Center for Biotechnology Information at the National Library of Medicine of the National Institutes of Health) searches for similarity to sequences contained in the BLAST “nr” database (comprising all non-redundant GenBank CDS translations, sequences derived from the 3-dimensional structure Brookhaven Protein Data Bank, the last major release of the SWISS-PROT protein sequence database, EMBL, and DDBJ databases). The cDNA sequences obtained as described in Example 11 were analyzed for similarity to all publicly available DNA sequences contained in the “nr” database using the BLASTN algorithm provided by the National Center for Biotechnology Information (NCBI). The DNA sequences were translated in all reading frames and compared for similarity to all publicly available protein sequences contained in the “nr” database using the BLASTX algorithm (Gish and States (1993)  Nat. Genet.  3:266-272) provided by the NCBI. For convenience, the P-value (probability) of observing a match of a cDNA sequence to a sequence contained in the searched databases merely by chance as calculated by BLAST are reported herein as “p Log” values, which represent the negative of the logarithm of the reported P-value. Accordingly, the greater the p Log value, the greater the likelihood that the cDNA sequence and the BLAST “hit” represent homologous proteins. 
     ESTs submitted for analysis are compared to the Genbank database as described above. ESTs that contain sequences more 5- or 3-prime can be found by using the BLASTn algorithm (Altschul et al (1997)  Nucleic Acids Res.  25:3389-3402.) against the Du Pont proprietary database comparing nucleotide sequences that share common or overlapping regions of sequence homology. Where common or overlapping sequences exist between two or more nucleic acid fragments, the sequences can be assembled into a single contiguous nucleotide sequence, thus extending the original fragment in either the 5 or 3 prime direction. Once the most 5-prime EST is identified, its complete sequence can be determined by Full Insert Sequencing as described in Example 6. Homologous genes belonging to different species can be found by comparing the amino acid sequence of a known gene (from either a proprietary source or a public database) against an EST database using the tBLASTn algorithm. The tBLASTn algorithm searches an amino acid query against a nucleotide database that is translated in all 6 reading frames. This search allows for differences in nucleotide codon usage between different species, and for codon degeneracy. 
     Example 13 
     Preparation of a Plant Expression Vector 
     A PCR product obtained using methods that are known by one skilled in the art can be combined with the Gateway® donor vector, such as pDONR™/Zeo (Invitrogen™). Using the Invitrogen™ Gateway® Clonase™ technology, the homologous At1g67330 gene from the entry clone can then be transferred to a suitable destination vector to obtain a plant expression vector for use with  Arabidopsis  and corn. For example, an expression vector contains At1g67330 expressed by the maize ubiquitin promoter, a herbicide resistance cassette and a seed sorting cassette. 
     Example 14 
       Agrobacterium  Mediated Transformation into Maize 
     Maize plants can be transformed to overexpress a validated  Arabidopsis  lead gene or the corresponding homologs from various species in order to examine the resulting phenotype. 
       Agrobacterium -mediated transformation of maize is performed essentially as described by Zhao et al., in  Meth. Mol. Biol.  318:315-323 (2006) (see also Zhao et al.,  Mol. Breed.  8:323-333 (2001) and U.S. Pat. No. 5,981,840 issued Nov. 9, 1999, incorporated herein by reference). The transformation process involves bacterium innoculation, co-cultivation, resting, selection and plant regeneration. 
     1. Immature Embryo Preparation 
     Immature embryos are dissected from caryopses and placed in a 2 mL microtube containing 2 mL PHI-A medium. 
     2.  Agrobacterium  Infection and Co-Cultivation of Embryos 
     2.1 Infection Step 
     PHI-A medium is removed with 1 mL micropipettor and 1 mL  Agrobacterium  suspension is added. Tube is gently inverted to mix. The mixture is incubated for 5 min at room temperature. 
     2.2 Co-Culture Step 
     The  Agrobacterium  suspension is removed from the infection step with a 1 mL micropipettor. Using a sterile spatula the embryos are scraped from the tube and transferred to a plate of PHI-B medium in a 100×15 mm Petri dish. The embryos are oriented with the embryonic axis down on the surface of the medium. Plates with the embryos are cultured at 20° C., in darkness, for 3 days. L-Cysteine can be used in the co-cultivation phase. With the standard binary vector, the co-cultivation medium supplied with 100-400 mg/L L-cysteine is critical for recovering stable transgenic events. 
     3. Selection of Putative Transgenic Events 
     To each plate of PHI-D medium in a 100×15 mm Petri dish, 10 embryos are transferred, maintaining orientation and the dishes are sealed with Parafilm. The plates are incubated in darkness at 28° C. Actively growing putative events, as pale yellow embryonic tissue are expected to be visible in 6-8 weeks. Embryos that produce no events may be brown and necrotic, and little friable tissue growth is evident. Putative transgenic embryonic tissue is subcultured to fresh PHI-D plates at 2-3 week intervals, depending on growth rate. The events are recorded. 
     4. Regeneration of T0 Plants 
     Embryonic tissue propagated on PHI-D medium is subcultured to PHI-E medium (somatic embryo maturation medium); in 100×25 mm Petri dishes and incubated at 28° C., in darkness, until somatic embryos mature, for about 10-18 days. Individual, matured somatic embryos with well-defined scutellum and coleoptile are transferred to PHI-F embryo germination medium and incubated at 28° C. in the light (about 80 μE from cool white or equivalent fluorescent lamps). In 7-10 days, regenerated plants, about 10 cm tall, are potted in horticultural mix and hardened-off using standard horticultural methods. 
     Media for Plant Transformation 
     
         
         
           
             1. PHI-A: 4 g/L CHU basal salts, 1.0 mL/L 1000× Eriksson&#39;s vitamin mix, 0.5 mg/L thiamin HCL, 1.5 mg/L 2,4-D, 0.69 g/L L-proline, 68.5 g/L sucrose, 36 g/L glucose, pH 5.2. Add 100 μM acetosyringone, filter-sterilized before using. 
             2. PHI-B: PHI-A without glucose, increased 2,4-D to 2 mg/L, reduced sucrose to 30 g/L and supplemented with 0.85 mg/L silver nitrate (filter-sterilized), 3.0 g/L gelrite, 100 μM acetosyringone (filter-sterilized), 5.8. 
             3. PHI-C: PHI-B without gelrite and acetosyringonee, reduced 2,4-D to 1.5 mg/L and supplemented with 8.0 g/L agar, 0.5 g/L Ms-morpholino ethane sulfonic acid (MES) buffer, 100 mg/L carbenicillin (filter-sterilized). 
             4. PHI-D: PHI-C supplemented with 3 mg/L bialaphos (filter-sterilized). 
             5. PHI-E: 4.3 g/L of Murashige and Skoog (MS) salts, (Gibco, BRL 11117-074), 0.5 mg/L nicotinic acid, 0.1 mg/L thiamine HCl, 0.5 mg/L pyridoxine HCl, 2.0 mg/L glycine, 0.1 g/L myo-inositol, 0.5 mg/L zeatin (Sigma, cat. no. Z-0164), 1 mg/L indole acetic acid (IAA), 26.4 μg/L abscisic acid (ABA), 60 g/L sucrose, 3 mg/L bialaphos (filter-sterilized), 100 mg/L carbenicillin (fileter-sterilized), 8 g/L agar, pH 5.6. 
             6. PHI-F: PHI-E without zeatin, IAA, ABA; sucrose reduced to 40 g/L; replacing agar with 1.5 g/L gelrite; pH 5.6. 
           
         
       
    
     Plants can be regenerated from the transgenic callus by first transferring clusters of tissue to N6 medium supplemented with 0.2 mg per liter of 2,4-D. After two weeks the tissue can be transferred to regeneration medium (Fromm et al. (1990)  Bio/Technology  8:833-839). 
     Phenotypic Analysis of Transgenic T0 Plants and T1 Plants can be Performed. 
     T1 plants can be analyzed for phenotypic changes. Using image analysis T1 plants can be analyzed for phenotypical changes in plant area, volume, growth rate and color analysis can be taken at multiple times during growth of the plants. Alteration in root architecture can be assayed as described herein. 
     Subsequent analysis of alterations in agronomic characteristics can be done to determine whether plants containing the validated  Arabidopsis  lead gene have an improvement of at least one agronomic characteristic, when compared to the control (or reference) plants that do not contain the validated  Arabidopsis  lead gene. The alterations may also be studied under various environmental conditions. 
     Expression constructs containing At1g67330 that result in a significant alteration in root and/or shoot biomass, improved green color, larger ear at anthesis or yield will be considered evidence that the  Arabidopsis  gene functions in maize to alter nitrogen use efficiency. 
     Example 15 
     Transformation of Maize with Validated  Arabidopsis  Lead Genes Using Particle Bombardment 
     Maize plants can be transformed to overexpress a validated  Arabidopsis  lead gene or the corresponding homologs from various species in order to examine the resulting phenotype. 
     The Gateway® entry clones described in Example 13 can be used to directionally clone each gene into a maize transformation vector. Expression of the gene in maize can be under control of a constitutive promoter such as the maize ubiquitin promoter (Christensen et al.,  Plant Mol. Biol.  12:619-632 (1989) and Christensen et al.,  Plant Mol. Biol.  18:675-689 (1992)) 
     The recombinant DNA construct described above can then be introduced into maize cells by the following procedure. Immature maize embryos can be dissected from developing caryopses derived from crosses of the inbred maize lines H99 and LH132. The embryos are isolated ten to eleven days after pollination when they are 1.0 to 1.5 mm long. The embryos are then placed with the axis-side facing down and in contact with agarose-solidified N6 medium (Chu et al.,  Sci. Sin. Peking  18:659-668 (1975)). The embryos are kept in the dark at 27° C. Friable embryogenic callus consisting of undifferentiated masses of cells with somatic proembryoids and embryoids borne on suspensor structures proliferates from the scutellum of these immature embryos. The embryogenic callus isolated from the primary explant can be cultured on N6 medium and sub-cultured on this medium every two to three weeks. 
     The plasmid, p35S/Ac (obtained from Dr. Peter Eckes, Hoechst Ag, Frankfurt, Germany) may be used in transformation experiments in order to provide for a selectable marker. This plasmid contains the pat gene (see European Patent Publication 0 242 236) which encodes phosphinothricin acetyl transferase (PAT). The enzyme PAT confers resistance to herbicidal glutamine synthetase inhibitors such as phosphinothricin. The pat gene in p35S/Ac is under the control of the 35S promoter from cauliflower mosaic virus (Odell et al.,  Nature  313:810-812 (1985)) and the 3′ region of the nopaline synthase gene from the T-DNA of the Ti plasmid of  Agrobacterium tumefaciens.    
     The particle bombardment method (Klein et al.,  Nature  327:70-73 (1987)) may be used to transfer genes to the callus culture cells. According to this method, gold particles (1 μm in diameter) are coated with DNA using the following technique. Ten μg of plasmid DNAs are added to 50 μL of a suspension of gold particles (60 mg per mL). Calcium chloride (50 μL of a 2.5 M solution) and spermidine free base (20 μL of a 1.0 M solution) are added to the particles. The suspension is vortexed during the addition of these solutions. After ten minutes, the tubes are briefly centrifuged (5 sec at 15,000 rpm) and the supernatant removed. The particles are resuspended in 200 μL of absolute ethanol, centrifuged again and the supernatant removed. The ethanol rinse is performed again and the particles resuspended in a final volume of 30 μL of ethanol. An aliquot (5 μL) of the DNA-coated gold particles can be placed in the center of a Kapton™ flying disc (Bio-Rad Labs). The particles are then accelerated into the maize tissue with a Biolistic® PDS-1000/He (Bio-Rad Instruments, Hercules Calif.), using a helium pressure of 1000 psi, a gap distance of 0.5 cm and a flying distance of 1.0 cm. 
     For bombardment, the embryogenic tissue is placed on filter paper over agarose-solidified N6 medium. The tissue is arranged as a thin lawn and covered a circular area of about 5 cm in diameter. The petri dish containing the tissue can be placed in the chamber of the PDS-1000/He approximately 8 cm from the stopping screen. The air in the chamber is then evacuated to a vacuum of 28 inches of Hg. The macrocarrier is accelerated with a helium shock wave using a rupture membrane that bursts when the He pressure in the shock tube reaches 1000 psi. 
     Seven days after bombardment the tissue can be transferred to N6 medium that contains bialaphos (5 mg per liter) and lacks casein or proline. The tissue continues to grow slowly on this medium. After an additional two weeks the tissue can be transferred to fresh N6 medium containing bialaphos. After six weeks, areas of about 1 cm in diameter of actively growing callus can be identified on some of the plates containing the bialaphos-supplemented medium. These calli may continue to grow when sub-cultured on the selective medium. 
     Plants can be regenerated from the transgenic callus by first transferring clusters of tissue to N6 medium supplemented with 0.2 mg per liter of 2,4-D. After two weeks the tissue can be transferred to regeneration medium (Fromm et al., Bio/Technology 8:833-839 (1990)). Transgenic T0 plants can be regenerated and their phenotype determined following HTP procedures. T1 seed can be collected. 
     T1 plants can be grown and analyzed for phenotypic changes. The following parameters can be quantified using image analysis: plant area, volume, growth rate and color analysis can be collected and quantified. Expression constructs that result in an alteration of root architecture or any one of the agronomic characteristics listed above compared to suitable control plants, can be considered evidence that the  Arabidopsis  lead gene functions in maize to alter root architecture or plant architecture. 
     Furthermore, a recombinant DNA construct containing a validated  Arabidopsis  gene can be introduced into an maize line either by direct transformation or introgression from a separately transformed line. 
     Transgenic plants, either inbred or hybrid, can undergo more vigorous field-based experiments to study root or plant architecture, yield enhancement and/or resistance to root lodging under various environmental conditions (e.g. variations in nutrient and water availability). 
     Subsequent yield analysis can also be done to determine whether plants that contain the validated  Arabidopsis  lead gene have an improvement in yield performance, when compared to the control (or reference) plants that do not contain the validated  Arabidopsis  lead gene. Plants containing the validated  Arabidopsis  lead gene would improved yield relative to the control plants, preferably 50% less yield loss under adverse environmental conditions or would have increased yield relative to the control plants under varying environmental conditions. 
     Example 16 
     Electroporation of  Agrobacterium tumefaciens  LBA4404 
     Electroporation competent cells (40 μl), such as  Agrobacterium tumefaciens  LBA4404 (containing PHP10523), are thawn on ice (20-30 min). PHP10523 contains VIR genes for T-DNA transfer, an  Agrobacterium  low copy number plasmid origin of replication, a tetracycline resistance gene, and a cos site for in vivo DNA biomolecular recombination. Meanwhile the electroporation cuvette is chilled on ice. The electroporator settings are adjusted to 2.1 kV. 
     A DNA aliquot (0.5 μL JT (U.S. Pat. No. 7,087,812) parental DNA at a concentration of 0.2 μg-1.0 μg in low salt buffer or twice distilled H 2 O) is mixed with the thawn  Agrobacterium  cells while still on ice. The mix is transferred to the bottom of electroporation cuvette and kept at rest on ice for 1-2 min. The cells are electroporated (Eppendorf electroporator 2510) by pushing “Pulse” button twice (ideally achieving a 4.0 msec pulse). Subsequently 0.5 ml 2×YT medium (or SOCmedium) are added to cuvette and transferred to a 15 ml Falcon tube. The cells are incubated at 28-30° C., 200-250 rpm for 3 h. 
     Aliquots of 250 μl are spread onto #30B (YM+50 μg/mL Spectinomycin) plates and incubated 3 days at 28-30° C. To increase the number of transformants one of two optional steps can be performed: 
     Option 1: overlay plates with 30 μl of 15 mg/ml Rifampicin. LBA4404 has a chromosomal resistance gene for Rifampicin. This additional selection eliminates some contaminating colonies observed when using poorer preparations of LBA4404 competent cells.
 
Option 2: Perform two replicates of the electroporation to compensate for poorer electrocompetent cells.
 
     Identification of Transformants: 
     Four independent colonies are picked and streaked on AB minimal medium plus 50 mg/mL Spectinomycin plates (#12S medium) for isolation of single colonies. The plated are incubate at 28° C. for 2-3 days. 
     A single colony for each putative co-integrate is picked and inoculated with 4 ml #60A with 50 mg/l Spectinomycin. The mix is incubated for 24 h at 28° C. with shaking. Plasmid DNA from 4 ml of culture is isolated using Qiagen Miniprep+optional PB wash. The DNA is eluted in 30 μl. Aliquots of 2 μl are used to electroporate 20 μl of DH10b+20 μl of ddH 2 O as per above. 
     Optionally a 15 μl aliquot can be used to transform 75-100 μl of Invitrogen™ Library Efficiency DH5a. The cells are spread on LB medium plus 50 mg/mL Spectinomycin plates (#34T medium) and incubated at 37° C. overnight. 
     Three to four independent colonies are picked for each putative co-integrate and inoculated 4 ml of 2×YT (#60A) with 50 μg/ml Spectinomycin. The cells are incubated at 37° C. overnight with shaking. 
     The plasmid DNA is isolated from 4 ml of culture using QIAprep® Miniprep with optional PB wash (elute in 50 μl) and 8 μl are used for digestion with SalI (using JT parent and PHP10523 as controls). 
     Three more digestions using restriction enzymes BamHI, EcoRI, and HindIII are performed for 4 plasmids that represent 2 putative co-integrates with correct SalI digestion pattern (using parental DNA and PHP10523 as controls). Electronic gels are recommended for comparison. 
     Example 17 
     Transformation of Gaspe Bay Flint Derived Maize Lines with Validated  Arabidopsis  Lead Genes and Corresponding Homologs from Other Species 
     Maize plants can be transformed as described in Example 14-16 overexpressing the  Arabidopsis  AT1G67330 gene and the corresponding homologs from other species, such as the ones listed in Table 1, in order to examine the resulting phenotype. Promoters including but not limited to the S2B promoter, the maize ROOTMET2 promoter, the maize Cyclo, the CR1BIO, the CRWAQ81 and others are useful for directing expression of homologs of At1 g67330 in maize. Furthermore, a variety of terminators, such as, but not limited to the PINII terminator, can be used to achieve expression of the gene of interest in Gaspe Bay Flint Derived Maize Lines. 
     Recipient Plants 
     Recipient plant cells can be from a uniform maize line having a short life cycle (“fast cycling”), a reduced size, and high transformation potential. Typical of these plant cells for maize are plant cells from any of the publicly available Gaspe Bay Flint (GBF) line varieties. One possible candidate plant line variety is the F1 hybrid of GBF×QTM (Quick Turnaround Maize, a publicly available form of Gaspe Bay Flint selected for growth under greenhouse conditions) disclosed in Tomes et al. U.S. Patent Application Publication No. 2003/0221212. Transgenic plants obtained from this line are of such a reduced size that they can be grown in four inch pots (¼ the space needed for a normal sized maize plant) and mature in less than 2.5 months. (Traditionally 3.5 months is required to obtain transgenic T0 seed once the transgenic plants are acclimated to the greenhouse.) Another suitable line is a double haploid line of GS3 (a highly transformable line) X Gaspe Flint. Yet another suitable line is a transformable elite inbred line carrying a transgene which causes early flowering, reduced stature, or both. 
     Transformation Protocol 
     Any suitable method may be used to introduce the transgenes into the maize cells, including but not limited to inoculation type procedures using  Agrobacterium  based vectors as described in Example 14 and 15. Transformation may be performed on immature embryos of the recipient (target) plant. 
     Precision Growth and Plant Tracking 
     The event population of transgenic (T0) plants resulting from the transformed maize embryos is grown in a controlled greenhouse environment using a modified randomized block design to reduce or eliminate environmental error. A randomized block design is a plant layout in which the experimental plants are divided into groups (e.g., thirty plants per group), referred to as blocks, and each plant is randomly assigned a location with the block. 
     For a group of thirty plants, twenty-four transformed, experimental plants and six control plants (plants with a set phenotype) (collectively, a “replicate group”) are placed in pots which are arranged in an array (a.k.a. a replicate group or block) on a table located inside a greenhouse. Each plant, control or experimental, is randomly assigned to a location with the block which is mapped to a unique, physical greenhouse location as well as to the replicate group. Multiple replicate groups of thirty plants each may be grown in the same greenhouse in a single experiment. The layout (arrangement) of the replicate groups should be determined to minimize space requirements as well as environmental effects within the greenhouse. Such a layout may be referred to as a compressed greenhouse layout. 
     An alternative to the addition of a specific control group is to identify those transgenic plants that do not express the gene of interest. A variety of techniques such as RT-PCR can be applied to quantitatively assess the expression level of the introduced gene. T0 plants that do not express the transgene can be compared to those which do. 
     Each plant in the event population is identified and tracked throughout the evaluation process, and the data gathered from that plant is automatically associated with that plant so that the gathered data can be associated with the transgene carried by the plant. For example, each plant container can have a machine readable label (such as a Universal Product Code (UPC) bar code) which includes information about the plant identity, which in turn is correlated to a greenhouse location so that data obtained from the plant can be automatically associated with that plant. 
     Alternatively any efficient, machine readable, plant identification system can be used, such as two-dimensional matrix codes or even radio frequency identification tags (RFID) in which the data is received and interpreted by a radio frequency receiver/processor. See U.S. Published Patent Application No. 2004/0122592, incorporated herein by reference. 
     Phenotypic Analysis Using Three-Dimensional Imaging 
     Each greenhouse plant in the T0 event population, including any control plants, is analyzed for agronomic characteristics of interest, and the agronomic data for each plant is recorded or stored in a manner so that it is associated with the identifying data (see above) for that plant. Confirmation of a phenotype (gene effect) can be accomplished in the T1 generation with a similar experimental design to that described above. 
     The T0 plants are analyzed at the phenotypic level using quantitative, non-destructive imaging technology throughout the plant&#39;s entire greenhouse life cycle to assess the traits of interest. Preferably, a digital imaging analyzer is used for automatic multi-dimensional analyzing of total plants. The imaging may be done inside the greenhouse. Two camera systems, located at the top and side, and an apparatus to rotate the plant, are used to view and image plants from all sides. Images are acquired from the top, front and side of each plant. All three images together provide sufficient information to evaluate the biomass, size and morphology of each plant. 
     Due to the change in size of the plants from the time the first leaf appears from the soil to the time the plants are at the end of their development, the early stages of plant development are best documented with a higher magnification from the top. This may be accomplished by using a motorized zoom lens system that is fully controlled by the imaging software. 
     In a single imaging analysis operation, the following events occur: (1) the plant is conveyed inside the analyzer area, rotated 360 degrees so its machine readable label can be read, and left at rest until its leaves stop moving; (2) the side image is taken and entered into a database; (3) the plant is rotated 90 degrees and again left at rest until its leaves stop moving, and (4) the plant is transported out of the analyzer. 
     Plants are allowed at least six hours of darkness per twenty four hour period in order to have a normal day/night cycle. 
     Imaging Instrumentation 
     Any suitable imaging instrumentation may be used, including but not limited to light spectrum digital imaging instrumentation commercially available from LemnaTec GmbH of Wurselen, Germany. The images are taken and analyzed with a LemnaTec Scanalyzer HTS LT-0001-2 having a ½″ IT Progressive Scan IEE CCD imaging device. The imaging cameras may be equipped with a motor zoom, motor aperture and motor focus. All camera settings may be made using LemnaTec software. Preferably, the instrumental variance of the imaging analyzer is less than about 5% for major components and less than about 10% for minor components. 
     Software 
     The imaging analysis system comprises a LemnaTec HTS Bonit software program for color and architecture analysis and a server database for storing data from about 500,000 analyses, including the analysis dates. The original images and the analyzed images are stored together to allow the user to do as much reanalyzing as desired. The database can be connected to the imaging hardware for automatic data collection and storage. A variety of commercially available software systems (e.g. Matlab, others) can be used for quantitative interpretation of the imaging data, and any of these software systems can be applied to the image data set. 
     Conveyor System 
     A conveyor system with a plant rotating device may be used to transport the plants to the imaging area and rotate them during imaging. For example, up to four plants, each with a maximum height of 1.5 m, are loaded onto cars that travel over the circulating conveyor system and through the imaging measurement area. In this case the total footprint of the unit (imaging analyzer and conveyor loop) is about 5 m×5 m. 
     The conveyor system can be enlarged to accommodate more plants at a time. The plants are transported along the conveyor loop to the imaging area and are analyzed for up to 50 seconds per plant. Three views of the plant are taken. The conveyor system, as well as the imaging equipment, should be capable of being used in greenhouse environmental conditions. 
     Illumination 
     Any suitable mode of illumination may be used for the image acquisition. For example, a top light above a black background can be used. Alternatively, a combination of top- and backlight using a white background can be used. The illuminated area should be housed to ensure constant illumination conditions. The housing should be longer than the measurement area so that constant light conditions prevail without requiring the opening and closing or doors. Alternatively, the illumination can be varied to cause excitation of either transgene (e.g., green fluorescent protein (GFP), red fluorescent protein (RFP)) or endogenous (e.g. Chlorophyll) fluorophores. 
     Biomass Estimation Based on Three-Dimensional Imaging 
     For best estimation of biomass the plant images should be taken from at least three axes, preferably the top and two side (sides 1 and 2) views. These images are then analyzed to separate the plant from the background, pot and pollen control bag (if applicable). The volume of the plant can be estimated by the calculation: 
       Volume(voxels)=√{square root over (TopArea(pixels))}×√{square root over (Side1Area(pixels))}×√{square root over (Side2Area(pixels))} 
     In the equation above the units of volume and area are “arbitrary units”. Arbitrary units are entirely sufficient to detect gene effects on plant size and growth in this system because what is desired is to detect differences (both positive-larger and negative-smaller) from the experimental mean, or control mean. The arbitrary units of size (e.g. area) may be trivially converted to physical measurements by the addition of a physical reference to the imaging process. For instance, a physical reference of known area can be included in both top and side imaging processes. Based on the area of these physical references a conversion factor can be determined to allow conversion from pixels to a unit of area such as square centimeters (cm 2 ). The physical reference may or may not be an independent sample. For instance, the pot, with a known diameter and height, could serve as an adequate physical reference. 
     Color Classification 
     The imaging technology may also be used to determine plant color and to assign plant colors to various color classes. The assignment of image colors to color classes is an inherent feature of the LemnaTec software. With other image analysis software systems color classification may be determined by a variety of computational approaches. 
     For the determination of plant size and growth parameters, a useful classification scheme is to define a simple color scheme including two or three shades of green and, in addition, a color class for chlorosis, necrosis and bleaching, should these conditions occur. A background color class which includes non plant colors in the image (for example pot and soil colors) is also used and these pixels are specifically excluded from the determination of size. The plants are analyzed under controlled constant illumination so that any change within one plant over time, or between plants or different batches of plants (e.g. seasonal differences) can be quantified. 
     In addition to its usefulness in determining plant size growth, color classification can be used to assess other yield component traits. For these other yield component traits additional color classification schemes may be used. For instance, the trait known as “staygreen”, which has been associated with improvements in yield, may be assessed by a color classification that separates shades of green from shades of yellow and brown (which are indicative of senescing tissues). By applying this color classification to images taken toward the end of the T0 or T1 plants&#39; life cycle, plants that have increased amounts of green colors relative to yellow and brown colors (expressed, for instance, as Green/Yellow Ratio) may be identified. Plants with a significant difference in this Green/Yellow ratio can be identified as carrying transgenes which impact this important agronomic trait. 
     The skilled plant biologist will recognize that other plant colors arise which can indicate plant health or stress response (for instance anthocyanins), and that other color classification schemes can provide further measures of gene action in traits related to these responses. 
     Plant Architecture Analysis 
     Transgenes which modify plant architecture parameters may also be identified using the present invention, including such parameters as maximum height and width, internodal distances, angle between leaves and stem, number of leaves starting at nodes and leaf length. The LemnaTec system software may be used to determine plant architecture as follows. The plant is reduced to its main geometric architecture in a first imaging step and then, based on this image, parameterized identification of the different architecture parameters can be performed. Transgenes that modify any of these architecture parameters either singly or in combination can be identified by applying the statistical approaches previously described. 
     Pollen Shed Date 
     Pollen shed date is an important parameter to be analyzed in a transformed plant, and may be determined by the first appearance on the plant of an active male flower. To find the male flower object, the upper end of the stem is classified by color to detect yellow or violet anthers. This color classification analysis is then used to define an active flower, which in turn can be used to calculate pollen shed date. 
     Alternatively, pollen shed date and other easily visually detected plant attributes (e.g. pollination date, first silk date) can be recorded by the personnel responsible for performing plant care. To maximize data integrity and process efficiency this data is tracked by utilizing the same barcodes utilized by the LemnaTec light spectrum digital analyzing device. A computer with a barcode reader, a palm device, or a notebook PC may be used for ease of data capture recording time of observation, plant identifier, and the operator who captured the data. 
     Orientation of the Plants 
     Mature maize plants grown at densities approximating commercial planting often have a planar architecture. That is, the plant has a clearly discernable broad side, and a narrow side. The image of the plant from the broadside is determined. To each plant a well defined basic orientation is assigned to obtain the maximum difference between the broadside and edgewise images. The top image is used to determine the main axis of the plant, and an additional rotating device is used to turn the plant to the appropriate orientation prior to starting the main image acquisition. 
     Example 18 
     Screening of Gaspe Bay Flint Derived Maize Lines Under Nitrogen Limiting Conditions 
     Transgenic plants will contain two or three doses of Gaspe Flint-3 with one dose of GS3 (GS3/(Gaspe-3)2X or GS3/(Gaspe-3)3X) and will segregate 1:1 for a dominant transgene. Plants will be planted in TURFACE®, a commercial potting medium, and watered four times each day with 1 mM KNO 3  growth medium and with 2 mM KNO 3 , or higher, growth medium. Control plants grown in 1 mM KNO 3  medium will be less green, produce less biomass and have a smaller ear at anthesis. Statistical analysis is used to decide if differences seen between treatments are really different. 
     Expression of a transgene will result in plants with improved plant growth in 1 mM KNO 3  when compared to a transgenic null. Thus biomass and greenness will be monitored during growth and compared to a transgenic null. Improvements in growth, greenness and ear size at anthesis will be indications of increased nitrogen tolerance. 
     Example 19 
     Transgenic Maize Plants 
     T 0  transgenic maize plants containing the nitrate uptake-associated construct under the control of a promoter were generated. These plants were grown in greenhouse conditions, under the FASTCORN system, as detailed in U.S. Patent Application Publication 2003/0221212, U.S. patent application Ser. No. 10/367,417. 
     Each of the plants was analyzed for measurable alteration in one or more of the following characteristics in the following manner: 
     T 1  progeny derived from self fertilization each T 0  plant containing a single copy of each nitrate uptake-associated construct that were found to segregate 1:1 for the transgenic event were analyzed for improved growth rate in low KNO 3 . Growth was monitored up to anthesis when cumulative plant growth, growth rate and ear weight were determined for transgene positive, transgene null, and non-transformed controls events. The distribution of the phenotype of individual plants was compared to the distribution of a control set and to the distribution of all the remaining treatments. Variances for each set were calculated and compared using an F test, comparing the event variance to a non-transgenic control set variance and to the pooled variance of the remaining events in the experiment. The greater the response to KNO 3 , the greater the variance within an event set and the greater the F value. Positive results will be compared to the distribution of the transgene within the event to make sure the response segregates with the transgene. 
     Example 20 
     Greenhouse Studies 
     Maize transgenic plants expressing At1g67330 driven by the maize ubiquitin promoter were analyzed for different parameters including but not limited to color, total surface area, growth rate, ear measurements and shoot fresh weight as described in example 17, 18 and 19. 
     Maize transgenic plants containing At1g67330 driven by the maize ubiquitin promoter showed differences in color. Under limiting nitrate conditions, null segregants show a decrease in green and an increase in light green. Positive segregants demonstrated significant improvements for % green under low nitrogen conditions. Events which had the highest levels of expression showed a significant decrease in light green under low nitrogen conditions. Some plants appeared to grow more slowly than null segregants as seen in SGR, total surface area and shoot fresh weight; however, ear growth was significantly greater under low nitrogen conditions. Under optimal nitrogen conditions some plants demonstrated a significant reduction in ear growth. Although some transgenic plants exhibited a reduction in ear growth, positive segregants showed improved performance for SGR, total surface area and shoot fresh weight under optimal nitrogen conditions. 
     Example 21 
     Transgenic Event Analysis from Field Plots 
     Transgenic events are evaluated in field plots where yield is limited by reducing fertilizer application by 30% or more. Improvements in yield, yield components, or other agronomic traits between transgenic and non-transgenic plants in these reduced nitrogen fertility plots are used to assess improvements in nitrogen utilization contributed by expression of transgenic events. Similar comparisons are made in plots supplemented with recommended nitrogen fertility rates. Effective transgenic events are those that achieve similar yields in the nitrogen-limited and normal nitrogen experiments. 
     Example 22 
     Field Studies 
     Under normal nitrogen conditions, maize transgenic plants expressing At1g67330 driven by the maize ubiquitin promoter showed a significant increase in yield when compared to controls. Maize transgenics expressing maize pco639489 driven by the maize ubiquitin promoter showed a significant increase in yield when compared to controls under reduced nitrogen conditions. 
     In a second year of field evaluation maize transgenic plants expressing maize pco639489 driven by the maize ubiquitin promoter showed a significant increase in yield when compared to controls under reduced nitrogen conditions. However, there was also a significant decrease in yield in one assay when compared to controls under reduced nitrogen conditions. 
     Example 23 
     Assays to Determine Alterations of Root Architecture in Maize 
     Transgenic maize plants are assayed for changes in root architecture at seedling stage, flowering time or maturity. Assays to measure alterations of root architecture of maize plants include, but are not limited to the methods outlined below. To facilitate manual or automated assays of root architecture alterations, corn plants can be grown in clear pots.
         1) Root mass (dry weights). Plants are grown in Turface®, a growth media that allows easy separation of roots. Oven-dried shoot and root tissues are weighed and a root/shoot ratio calculated.   2) Levels of lateral root branching. The extent of lateral root branching (e.g. lateral root number, lateral root length) is determined by sub-sampling a complete root system, imaging with a flat-bed scanner or a digital camera and analyzing with WinRHIZO™ software (Regent Instruments Inc.).   3) Root band width measurements. The root band is the band or mass of roots that forms at the bottom of greenhouse pots as the plants mature. The thickness of the root band is measured in mm at maturity as a rough estimate of root mass.   4) Nodal root count. The number of crown roots coming off the upper nodes can be determined after separating the root from the support medium (e.g. potting mix). In addition the angle of crown roots and/or brace roots can be measured. Digital analysis of the nodal roots and amount of branching of nodal roots form another extension to the aforementioned manual method.       

     All data taken on root phenotype are subjected to statistical analysis, normally a t-test to compare the transgenic roots with that of non-transgenic sibling plants. One-way ANOVA may also be used in cases where multiple events and/or constructs are involved in the analysis. 
     Example 24 
     Soybean Embryo Transformation 
     Soybean embryos are bombarded with a plasmid containing an antisense nitrate uptake-associated sequences operably linked to an ubiquitin promoter as follows. To induce somatic embryos, cotyledons, 3-5 mm in length dissected from surface-sterilized, immature seeds of the soybean cultivar A2872, are cultured in the light or dark at 26° C. on an appropriate agar medium for six to ten weeks. Somatic embryos producing secondary embryos are then excised and placed into a suitable liquid medium. After repeated selection for clusters of somatic embryos that multiplied as early, globular-staged embryos, the suspensions are maintained as described below. 
     Soybean embryogenic suspension cultures can be maintained in 35 ml liquid media on a rotary shaker, 150 rpm, at 26° C. with florescent lights on a 16:8 hour day/night schedule. Cultures are subcultured every two weeks by inoculating approximately 35 mg of tissue into 35 ml of liquid medium. 
     Soybean embryogenic suspension cultures may then be transformed by the method of particle gun bombardment (Klein, et al., (1987)  Nature  (London) 327:70-73, U.S. Pat. No. 4,945,050). A Du Pont Biolistic PDS1000/HE instrument (helium retrofit) can be used for these transformations. 
     A selectable marker gene that can be used to facilitate soybean transformation is a transgene composed of the 35S promoter from Cauliflower Mosaic Virus (Odell, et al., (1985)  Nature  313:810-812), the hygromycin phosphotransferase gene from plasmid pJR225 (from  E. coli ; Gritz, et al., (1983)  Gene  25:179-188), and the 3′ region of the nopaline synthase gene from the T-DNA of the Ti plasmid of  Agrobacterium tumefaciens . The expression cassette comprising an antisense nitrate uptake-associated sequence operably linked to the ubiquitin promoter can be isolated as a restriction fragment. This fragment can then be inserted into a unique restriction site of the vector carrying the marker gene. 
     To 50 μl of a 60 mg/ml 1 μm gold particle suspension is added (in order): 5 μl DNA (1 μg/μl), 20 μl spermidine (0.1 M), and 50 μl CaCl 2  (2.5 M). The particle preparation is then agitated for three minutes, spun in a microfuge for 10 seconds and the supernatant removed. The DNA-coated particles are then washed once in 400 μl 70% ethanol and resuspended in 40 μl of anhydrous ethanol. The DNA/particle suspension can be sonicated three times for one second each. Five microliters of the to DNA-coated gold particles are then loaded on each macro carrier disk. 
     Approximately 300-400 mg of a two-week-old suspension culture is placed in an empty 60×15 mm petri dish and the residual liquid removed from the tissue with a pipette. For each transformation experiment, approximately 5-10 plates of tissue are normally bombarded. Membrane rupture pressure is set at 1100 psi, and the chamber is evacuated to a vacuum of 28 inches mercury. The tissue is placed approximately 3.5 inches away from the retaining screen and bombarded three times. Following bombardment, the tissue can be divided in half and placed back into liquid and cultured as described above. 
     Five to seven days post bombardment, the liquid media may be exchanged with fresh media, and eleven to twelve days post-bombardment with fresh media containing 50 mg/ml hygromycin. This selective media can be refreshed weekly. Seven to eight weeks post-bombardment, green, transformed tissue may be observed growing from untransformed, necrotic embryogenic clusters. Isolated green tissue is removed and inoculated into individual flasks to generate new, clonally propagated, transformed embryogenic suspension cultures. Each new line may be treated as an independent transformation event. These suspensions can then be subcultured and maintained as clusters of immature embryos or regenerated into whole plants by maturation and germination of individual somatic embryos. 
     Example 25 
     Sunflower Meristem Tissue Transformation 
     Sunflower meristem tissues are transformed with an expression cassette containing an antisense nitrate uptake-associated sequences operably linked to a ubiquitin promoter as follows (see also, European Patent Number EP 0 486233, herein incorporated by reference, and Malone-Schoneberg, et al., (1994) Plant Science 103:199-207). Mature sunflower seed ( Helianthus annuus  L.) are dehulled using a single wheat-head thresher. Seeds are surface sterilized for 30 minutes in a 20% Clorox bleach solution with the addition of two drops of Tween 20 per 50 ml of solution. The seeds are rinsed twice with sterile distilled water. 
     Split embryonic axis explants are prepared by a modification of procedures described by Schrammeijer, et al. (Schrammeijer, et al., (1990)  Plant Cell Rep.  9:55-60). Seeds are imbibed in distilled water for 60 minutes following the surface sterilization procedure. The cotyledons of each seed are then broken off, producing a clean fracture at the plane of the embryonic axis. Following excision of the root tip, the explants are bisected longitudinally between the primordial leaves. The two halves are placed, cut surface up, on GBA medium consisting of Murashige and Skoog mineral elements (Murashige, et al., (1962)  Physiol. Plant.,  15:473-497), Shepard&#39;s vitamin additions (Shepard, (1980) in  Emergent Techniques for the Genetic Improvement of Crops  (University of Minnesota Press, St. Paul, Minn.), 40 mg/l adenine sulfate, 30 g/l sucrose, 0.5 mg/l 6-benzyl-aminopurine (BAP), 0.25 mg/l indole-3-acetic acid (IAA), 0.1 mg/l gibberellic acid (GA 3 ), pH 5.6, and 8 g/l Phytagar. 
     The explants are subjected to microprojectile bombardment prior to  Agrobacterium  treatment (Bidney, et al., (1992)  Plant Mol. Biol.  18:301-313). Thirty to forty explants are placed in a circle at the center of a 60×20 mm plate for this treatment. Approximately 4.7 mg of 1.8 mm tungsten microprojectiles are resuspended in 25 ml of sterile TE buffer (10 mM Tris HCl, 1 mM EDTA, pH 8.0) and 1.5 ml aliquots are used per bombardment. Each plate is bombarded twice through a 150 mm nytex screen placed 2 cm above the samples in a PDS 1000® particle acceleration device. 
     Disarmed  Agrobacterium tumefaciens  strain EHA105 is used in all transformation experiments. A binary plasmid vector comprising the expression cassette that contains the nitrate uptake-associated gene operably linked to the ubiquitin promoter is introduced into  Agrobacterium  strain EHA105 via freeze-thawing as described by Holsters, et al., (1978)  Mol. Gen. Genet.  163:181-187. This plasmid further comprises a kanamycin selectable marker gene (i.e, nptII). Bacteria for plant transformation experiments are grown overnight (28° C. and 100 RPM continuous agitation) in liquid YEP medium (10 gm/l yeast extract, 10 gm/l Bactopeptone, and 5 gm/l NaCl, pH 7.0) with the appropriate antibiotics required for bacterial strain and binary plasmid maintenance. The suspension is used when it reaches an OD 600  of about 0.4 to 0.8. The  Agrobacterium  cells are pelleted and resuspended at a final OD 600  of 0.5 in an inoculation medium comprised of 12.5 mM MES pH 5.7, 1 gm/l NH 4 Cl, and 0.3 gm/l MgSO 4 . 
     Freshly bombarded explants are placed in an  Agrobacterium  suspension, mixed, and left undisturbed for 30 minutes. The explants are then transferred to GBA medium and co-cultivated, cut surface down, at 26° C. and 18-hour days. After three days of co-cultivation, the explants are transferred to 374B (GBA medium lacking growth regulators and a reduced sucrose level of 1%) supplemented with 250 mg/l cefotaxime and 50 mg/l kanamycin sulfate. The explants are cultured for two to five weeks on selection and then transferred to fresh 374B medium lacking kanamycin for one to two weeks of continued development. Explants with differentiating, antibiotic-resistant areas of growth that have not produced shoots suitable for excision are transferred to GBA medium containing 250 mg/l cefotaxime for a second 3-day phytohormone treatment. Leaf samples from green, kanamycin-resistant shoots are assayed for the presence of NPTII by ELISA and for the presence of transgene expression by assaying for a modulation in meristem development (i.e., an alteration of size and appearance of shoot and floral meristems). 
     NPTII-positive shoots are grafted to Pioneer® hybrid 6440 in vitro-grown sunflower seedling rootstock. Surface sterilized seeds are germinated in 48-0 medium (half-strength Murashige and Skoog salts, 0.5% sucrose, 0.3% gelrite, pH 5.6) and grown under conditions described for explant culture. The upper portion of the seedling is removed, a 1 cm vertical slice is made in the hypocotyl, and the transformed shoot inserted into the cut. The entire area is wrapped with parafilm to secure the shoot. Grafted plants can be transferred to soil following one week of in vitro culture. Grafts in soil are maintained under high humidity conditions followed by a slow acclimatization to the greenhouse environment. Transformed sectors of T 0  plants (parental generation) maturing in the greenhouse are identified by NPTII ELISA and/or by nitrate uptake-associated activity analysis of leaf extracts while transgenic seeds harvested from NPTII-positive T 0  plants are identified by nitrate uptake-associated activity analysis of small portions of dry seed cotyledon. 
     An alternative sunflower transformation protocol allows the recovery of transgenic progeny without the use of chemical selection pressure. Seeds are dehulled and surface-sterilized for 20 minutes in a 20% Clorox bleach solution with the addition of two to three drops of Tween 20 per 100 ml of solution, then rinsed three times with distilled water. Sterilized seeds are imbibed in the dark at 26° C. for 20 hours on filter paper moistened with water. The cotyledons and root radical are removed, and the meristem explants are cultured on 374E (GBA medium consisting of MS salts, Shepard vitamins, 40 mg/l adenine sulfate, 3% sucrose, 0.5 mg/l 6-BAP, 0.25 mg/l IAA, 0.1 mg/l GA, and 0.8% Phytagar at pH 5.6) for 24 hours under the dark. The primary leaves are removed to expose the apical meristem, around 40 explants are placed with the apical dome facing upward in a 2 cm circle in the center of 374M (GBA medium with 1.2% Phytagar), and then cultured on the medium for 24 hours in the dark. 
     Approximately 18.8 mg of 1.8 μm tungsten particles are resuspended in 150 μl absolute ethanol. After sonication, 8 μl of it is dropped on the center of the surface of macrocarrier. Each plate is bombarded twice with 650 psi rupture discs in the first shelf at 26 mm of Hg helium gun vacuum. 
     The plasmid of interest is introduced into  Agrobacterium tumefaciens  strain EHA105 via freeze thawing as described previously. The pellet of overnight-grown bacteria at 28° C. in a liquid YEP medium (10 g/l yeast extract, 10 g/l Bactopeptone, and 5 g/l NaCl, pH 7.0) in the presence of 50 μg/l kanamycin is resuspended in an inoculation medium (12.5 mM 2-mM 2-(N-morpholino) ethanesulfonic acid, MES, 1 g/l NH 4 Cl and 0.3 g/l MgSO 4  at pH 5.7) to reach a final concentration of 4.0 at OD 600. Particle-bombarded explants are transferred to GBA medium (374E), and a droplet of bacteria suspension is placed directly onto the top of the meristem. The explants are co-cultivated on the medium for 4 days, after which the explants are transferred to 374C medium (GBA with 1% sucrose and no BAP, IAA, GA3 and supplemented with 250 μg/ml cefotaxime). The plantlets are cultured on the medium for about two weeks under 16-hour day and 26° C. incubation conditions. 
     Explants (around 2 cm long) from two weeks of culture in 374C medium are screened for a modulation in meristem development (i.e., an alteration of size and appearance of shoot and floral meristems). After positive explants are identified, those shoots that fail to exhibit modified nitrate uptake-associated activity are discarded, and every positive explant is subdivided into nodal explants. One nodal explant contains at least one potential node. The nodal segments are cultured on GBA medium for three to four days to promote the formation of auxiliary buds from each node. Then they are transferred to 374C medium and allowed to develop for an additional four weeks. Developing buds are separated and cultured for an additional four weeks on 374C medium. Pooled leaf samples from each newly recovered shoot are screened again by the appropriate protein activity assay. At this time, the positive shoots recovered from a single node will generally have been enriched in the transgenic sector detected in the initial assay prior to nodal culture. 
     Recovered shoots positive for modified nitrate uptake-associated expression are grafted to Pioneer hybrid 6440 in vitro-grown sunflower seedling rootstock. The rootstocks are prepared in the following manner. Seeds are dehulled and surface-sterilized for 20 minutes in a 20% Clorox bleach solution with the addition of two to three drops of Tween 20 per 100 ml of solution, and are rinsed three times with distilled water. The sterilized seeds are germinated on the filter moistened with water for three days, then they are transferred into 48 medium (half-strength MS salt, 0.5% sucrose, 0.3% gelrite pH 5.0) and grown at 26° C. under the dark for three days, then incubated at 16-hour-day culture conditions. The upper portion of selected seedling is removed, a vertical slice is made in each hypocotyl, and a transformed shoot is inserted into a V-cut. The cut area is wrapped with parafilm. After one week of culture on the medium, grafted plants are transferred to soil. In the first two weeks, they are maintained under high humidity conditions to acclimatize to a greenhouse environment. 
     Example 26 
     Rice Tissue Transformation 
     Genetic Confirmation of the Nitrate Uptake-Associated Gene 
     One method for transforming DNA into cells of higher plants that is available to those skilled in the art is high-velocity ballistic bombardment using metal particles coated with the nucleic acid constructs of interest (see, Klein, et al.,  Nature  (1987) (London) 327:70-73, and see U.S. Pat. No. 4,945,050). A Biolistic PDS-1000/He (BioRAD Laboratories, Hercules, Calif.) is used for these complementation experiments. The particle bombardment technique is used to transform the nitrate uptake-associated mutants and wild type rice with DNA fragments 
     The bacterial hygromycin B phosphotransferase (Hpt II) gene from  Streptomyces hygroscopicus  that confers resistance to the antibiotic is used as the selectable marker for rice transformation. In the vector, pML18, the Hpt II gene was engineered with the 35S promoter from Cauliflower Mosaic Virus and the termination and polyadenylation signals from the octopine synthase gene of  Agrobacterium tumefaciens . pML18 was described in WO 97/47731, which was published on Dec. 18, 1997, the disclosure of which is hereby incorporated by reference. 
     Embryogenic callus cultures derived from the scutellum of germinating rice seeds serve as source material for transformation experiments. This material is generated by germinating sterile rice seeds on a callus initiation media (MS salts, Nitsch and Nitsch vitamins, 1.0 mg/l 2,4-D and 10 μM AgNO 3 ) in the dark at 27-28° C. Embryogenic callus proliferating from the scutellum of the embryos is the transferred to CM media (N6 salts, Nitsch and Nitsch vitamins, 1 mg/l 2,4-D, Chu, et al., 1985,  Sci. Sinica  18: 659-668). Callus cultures are maintained on CM by routine sub-culture at two week intervals and used for transformation within 10 weeks of initiation. 
     Callus is prepared for transformation by subculturing 0.5-1.0 mm pieces approximately 1 mm apart, arranged in a circular area of about 4 cm in diameter, in the center of a circle of Whatman #541 paper placed on CM media. The plates with callus are incubated in the dark at 27-28° C. for 3-5 days. Prior to bombardment, the filters with callus are transferred to CM supplemented with 0.25 M mannitol and 0.25 M sorbitol for 3 hr in the dark. The petri dish lids are then left ajar for 20-45 minutes in a sterile hood to allow moisture on tissue to dissipate. 
     Each genomic DNA fragment is co-precipitated with pML18 containing the selectable marker for rice transformation onto the surface of gold particles. To accomplish this, a total of 10 μg of DNA at a 2:1 ratio of trait:selectable marker DNAs are added to 50 μl aliquot of gold particles that have been resuspended at a concentration of 60 mg ml −1 . Calcium chloride (50 μl of a 2.5 M solution) and spermidine (20 μl of a 0.1 M solution) are then added to the gold-DNA suspension as the tube is vortexing for 3 min. The gold particles are centrifuged in a microfuge for 1 sec and the supernatant removed. The gold particles are then washed twice with 1 ml of absolute ethanol and then resuspended in 50 μl of absolute ethanol and sonicated (bath sonicator) for one second to disperse the gold particles. The gold suspension is incubated at −70° C. for five minutes and sonicated (bath sonicator) if needed to disperse the particles. Six μl of the DNA-coated gold particles are then loaded onto mylar macrocarrier disks and the ethanol is allowed to evaporate. 
     At the end of the drying period, a petri dish containing the tissue is placed in the chamber of the PDS-1000/He. The air in the chamber is then evacuated to a vacuum of 28-29 inches Hg. The macrocarrier is accelerated with a helium shock wave using a rupture membrane that bursts when the He pressure in the shock tube reaches 1080-1100 psi. The tissue is placed approximately 8 cm from the stopping screen and the callus is bombarded two times. Two to four plates of tissue are bombarded in this way with the DNA-coated gold particles. Following bombardment, the callus tissue is transferred to CM media without supplemental sorbitol or mannitol. 
     Within 3-5 days after bombardment the callus tissue is transferred to SM media (CM medium containing 50 mg/l hygromycin). To accomplish this, callus tissue is transferred from plates to sterile 50 ml conical tubes and weighed. Molten top-agar at 40° C. is added using 2.5 ml of top agar/100 mg of callus. Callus clumps are broken into fragments of less than 2 mm diameter by repeated dispensing through a 10 ml pipet. Three ml aliquots of the callus suspension are plated onto fresh SM media and the plates are incubated in the dark for 4 weeks at 27-28° C. After 4 weeks, transgenic callus events are identified, transferred to fresh SM plates and grown for an additional 2 weeks in the dark at 27-28° C. 
     Growing callus is transferred to RM1 media (MS salts, Nitsch and Nitsch vitamins, 2% sucrose, 3% sorbitol, 0.4% gelrite+50 ppm hyg B) for 2 weeks in the dark at 25° C. After 2 weeks the callus is transferred to RM2 media (MS salts, Nitsch and Nitsch vitamins, 3% sucrose, 0.4% gelrite+50 ppm hyg B) and placed under cool white light (˜40 μEm −2 s −1 ) with a 12 hr photo period at 25° C. and 30-40% humidity. After 2-4 weeks in the light, callus begin to organize, and form shoots. Shoots are removed from surrounding callus/media and gently transferred to RM3 media (½×MS salts, Nitsch and Nitsch vitamins, 1% sucrose+50 ppm hygromycin B) in phytatrays (Sigma Chemical Co., St. Louis, Mo.) and incubation is continued using the same conditions as described in the previous step. 
     Plants are transferred from RM3 to 4″ pots containing Metro mix 350 after 2-3 weeks, when sufficient root and shoot growth have occurred. The seed obtained from the transgenic plants is examined for genetic complementation of the nitrate uptake-associated mutation with the wild-type genomic DNA containing the nitrate uptake-associated gene. 
     Example 27 
     Variants of Nitrate Uptake-Associated Sequences 
     A. Variant Nucleotide Sequences of Nitrate Uptake-Associated Proteins that do not Alter the Encoded Amino Acid Sequence 
     The nitrate uptake-associated nucleotide sequences are used to generate variant nucleotide sequences having the nucleotide sequence of the open reading frame with about 70%, 75%, 80%, 85%, 90%, and 95% nucleotide sequence identity when compared to the starting unaltered ORF nucleotide sequence of the corresponding SEQ ID NO. These functional variants are generated using a standard codon table. While the nucleotide sequence of the variants are altered, the amino acid sequence encoded by the open reading frames do not change. 
     B. Variant Amino Acid Sequences of Nitrate Uptake-Associated Polypeptides 
     Variant amino acid sequences of the nitrate uptake-associated polypeptides are generated. In this example, one amino acid is altered. Specifically, the open reading frames are reviewed to determine the appropriate amino acid alteration. The selection of the amino acid to change is made by consulting the protein alignment (with the other orthologs and other gene family members from various species). An amino acid is selected that is deemed not to be under high selection pressure (not highly conserved) and which is rather easily substituted by an amino acid with similar chemical characteristics (i.e., similar functional side-chain). Using the protein alignment, an appropriate amino acid can be changed. Once the targeted amino acid is identified, the procedure outlined in the following section C is followed. Variants having about 70%, 75%, 80%, 85%, 90%, and 95% nucleic acid sequence identity are generated using this method. 
     C. Additional Variant Amino Acid Sequences of Nitrate Uptake-Associated Polypeptides 
     In this example, artificial protein sequences are created having 80%, 85%, 90%, and 95% identity relative to the reference protein sequence. This latter effort requires identifying conserved and variable regions from the alignment and then the judicious application of an amino acid substitutions table. These parts will be discussed in more detail below. 
     Largely, the determination of which amino acid sequences are altered is made based on the conserved regions among nitrate uptake-associated protein or among the other nitrate uptake-associated polypeptides. Based on the sequence alignment, the various regions of the nitrate uptake-associated polypeptide that can likely be altered are represented in lower case letters, while the conserved regions are represented by capital letters. It is recognized that conservative substitutions can be made in the conserved regions below without altering function. In addition, one of skill will understand that functional variants of the nitrate uptake-associated sequence of the invention can have minor non-conserved amino acid alterations in the conserved domain. 
     Artificial protein sequences are then created that are different from the original in the intervals of 80-85%, 85-90%, 90-95%, and 95-100% identity. Midpoints of these intervals are targeted, with liberal latitude of plus or minus 1%, for example. The amino acids substitutions will be effected by a custom Perl script. The substitution table is provided below in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Substitution Table 
               
            
           
           
               
               
               
               
            
               
                   
                 Strongly Similar 
                 Rank of 
                   
               
               
                 Amino 
                 and Optimal 
                 Order to 
               
               
                 Acid 
                 Substitution 
                 Change 
                 Comment 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 I 
                 L, V 
                 1 
                 50:50 substitution 
               
               
                 L 
                 I, V 
                 2 
                 50:50 substitution 
               
               
                 V 
                 I, L 
                 3 
                 50:50 substitution 
               
               
                 A 
                 G 
                 4 
               
               
                 G 
                 A 
                 5 
               
               
                 D 
                 E 
                 6 
               
               
                 E 
                 D 
                 7 
               
               
                 W 
                 Y 
                 8 
               
               
                 Y 
                 W 
                 9 
               
               
                 S 
                 T 
                 10 
               
               
                 T 
                 S 
                 11 
               
               
                 K 
                 R 
                 12 
               
               
                 R 
                 K 
                 13 
               
               
                 N 
                 Q 
                 14 
               
               
                 Q 
                 N 
                 15 
               
               
                 F 
                 Y 
                 16 
               
               
                 M 
                 L 
                 17 
                 First methionine cannot change 
               
               
                 H 
                   
                 Na 
                 No good substitutes 
               
               
                 C 
                   
                 Na 
                 No good substitutes 
               
               
                 P 
                   
                 Na 
                 No good substitutes 
               
               
                   
               
            
           
         
       
     
     First, any conserved amino acids in the protein that should not be changed is identified and “marked off” for insulation from the substitution. The start methionine will of course be added to this list automatically. Next, the changes are made. 
     H, C, and P are not changed in any circumstance. The changes will occur with isoleucine first, sweeping N-terminal to C-terminal. Then leucine, and so on down the list until the desired target it reached. Interim number substitutions can be made so as not to cause reversal of changes. The list is ordered 1-17, so start with as many isoleucine changes as needed before leucine, and so on down to methionine. Clearly many amino acids will in this manner not need to be changed. L, I and V will involve a 50:50 substitution of the two alternate optimal substitutions. 
     The variant amino acid sequences are written as output. Perl script is used to calculate the percent identities. Using this procedure, variants of the nitrate uptake-associated polypeptides are generating having about 80%, 85%, 90%, and 95% amino acid identity to the starting unaltered ORF nucleotide sequence of SEQ ID NOS:1. 
     All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated by reference. 
     The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.