Patent Publication Number: US-2022220496-A1

Title: Abiotic stress tolerant plants and methods

Description:
FIELD 
     The field of the disclosure relates to plant breeding and genetics and, particularly, relates to improving tolerance to abiotic stress in plants. 
     BACKGROUND 
     Stresses to plants may be caused by both biotic and abiotic agents. For example, biotic causes of stress include infection with pathogen, insect feeding, and parasitism by another plant such as mistletoe. Abiotic stresses include, for example, excessive or insufficient available water, temperature extremes, and synthetic chemicals such as herbicides. 
     Abiotic stress is the primary cause of crop loss worldwide, causing average yield losses more than 50% for major crops (Boyer, J. S. (1982)  Science  218:443-448; Bray, E. A. et al. (2000) In Biochemistry and Molecular Biology of Plants, edited by Buchannan, B. B. et al., Amer. Soc. Plant Biol., pp. 1158-1249). 
     Accordingly, there is a need to develop compositions and methods that increase tolerance to abiotic stress in plants. This invention provides such compositions and methods. 
     SUMMARY 
     The following embodiments are among those encompassed by the disclosure: 
     In one embodiment, the present disclosure includes an isolated polynucleotide, encoding a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24, wherein increased expression of the polynucleotide in a plant enhances nitrogen stress tolerance or improves nitrogen use efficiency (NUE). In certain embodiments, the isolated polynucleotide encodes the amino acid sequence of SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. In certain embodiments, the isolated polynucleotide comprises the nucleotide sequence of SEQ ID NO: 1, 2, 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 19, 20, 22 or 23. In certain embodiments, increased expression of the polynucleotide in a plant enhances grain yield under low nitrogen conditions and/or normal nitrogen conditions. 
     The present disclosure also provides a recombinant DNA construct comprising an isolated polynucleotide operably linked to at least one heterologous regulatory element, wherein the polynucleotide encodes a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. 
     The present disclosure further provides a modified plant or seed having increased expression or activity of at least one polynucleotide encoding a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. In certain embodiments, the modified plant or seed comprises in its genome a recombinant DNA construct comprising a polynucleotide operably linked to at least one heterologous regulatory element, wherein the polynucleotide encodes a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. In certain embodiments, the modified plant exhibits improved nitrogen stress tolerance, NUE, and/or increased grain yield when grown under low nitrogen conditions and/or normal nitrogen conditions compared to a control plant. 
     In certain embodiments, the modified plant or seed comprises a targeted genetic modification at a genomic locus comprising a polynucleotide encoding a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24, wherein the targeted genetic modification increase the expression and/or activity of the polypeptide. In certain embodiments, the modified plant exhibits improved nitrogen stress tolerance, NUE, and/or increased grain yield when grown under low nitrogen conditions and/or normal nitrogen conditions compared to a control plant. 
     In certain embodiments, the plant is selected from the group consisting of rice, maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, barley, millet, sugar cane and switchgrass. 
     Also provided are methods for increasing nitrogen stress tolerance or NUE in a plant, the method comprising increasing the expression of at least one polynucleotide encoding a polypeptide with amino acid sequence of at least 90% sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. Wherein the obtained plant exhibits increased nitrogen stress tolerance or NUE when compared to the control plant. 
     In certain embodiments, the method for increasing nitrogen stress tolerance or NUE comprises: (a) introducing into a regenerable plant cell a recombinant DNA construct comprising a polynucleotide operably linked to at least one heterologous regulatory element, wherein the polynucleotide encodes a polypeptide having an amino acid sequence of at least 80% sequence identity, when compared to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24; and (b) generating the plant, wherein the plant comprises in its genome the recombinant DNA construct. 
     In certain embodiments, the method for increasing nitrogen stress tolerance or NUE comprises: (a) introducing into a regenerable plant cell a targeted genetic modification at a genomic locus comprising a polynucleotide encoding a polypeptide having an amino acid sequence of at least 80% sequence identity, when compared to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24; and (b) generating the plant, wherein the plant comprises in its genome the introduced genetic modification and has increased expression and/or activity of the polypeptide. In certain embodiments, the targeted genetic modification is introduced using a genome modification technique selected from the group consisting of a polynucleotide-guided endonuclease, CRISPR-Cas endonucleases, base editing deaminases, a zinc finger nuclease, a transcription activator-like effector nuclease (TALEN), an engineered site-specific meganucleases, or an Argonaute. In certain embodiments, the targeted genetic modification is present in (a) the coding region; (b) a non-coding region; (c) a regulatory sequence; (d) an untranslated region; or (e) any combination of (a)-(d) of the genomic locus that encodes a polypeptide comprising an amino acid sequence that is at 80% sequence identity, when compared to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS AND SEQUENCE LISTING 
       The disclosure can be more fully understood from the following detailed description and the accompanying Sequence Listing which form a part of this application. The sequence descriptions and sequence listing attached hereto comply with the rules governing nucleotide and amino acid sequence disclosures in patent applications as set forth in 37 C.F.R. §§ 1.821 and 1.825. The sequence descriptions comprise the three letter codes for amino acids as defined in 37 C.F.R. §§ 1.821 and 1.825, which are incorporated herein by reference. 
       
         
           
             
                 
               
                 
                   TABLE 1 
                 
               
              
                 
                     
                 
                 
                   Sequence Listing Description 
                 
              
             
             
                 
                 
                 
                 
              
                 
                     
                     
                   SEQ ID NO: 
                   SEQ ID NO: 
                 
                 
                   Source species 
                   Clone Designation 
                   (Nucleotide) 
                   (Amino Acid) 
                 
                 
                     
                 
              
             
             
                 
                 
                 
                 
              
                 
                   
                     Oryza sativa 
                   
                   OsLNTP12 
                   1, 2 
                   3 
                 
                 
                   
                     Oryza sativa 
                   
                   OsLNTP13 
                   4, 5 
                   6 
                 
                 
                   
                     Oryza sativa 
                   
                   OsGRRP1 
                   7, 8 
                   9 
                 
                 
                   
                     Oryza sativa 
                   
                   OsLNTP14 
                   10, 11 
                   12 
                 
                 
                   
                     Oryza sativa 
                   
                   OsLNTP15 
                   13, 14 
                   15 
                 
                 
                   
                     Oryza sativa 
                   
                   OsLNTP16 
                   16, 17 
                   18 
                 
                 
                   
                     Oryza sativa 
                   
                   OsLNTP17 
                   19, 20 
                   21 
                 
                 
                   
                     Oryza sativa 
                   
                   OsPTR11 
                   22, 23 
                   24 
                 
                 
                   Artificial 
                   Primers 
                   25-46 
                   n/a 
                 
                 
                   
                     Oryza sativa 
                   
                   LNTP12 paralog 
                   47 
                   48 
                 
                 
                   
                     Oryza sativa 
                   
                   LNTP13 paralog 
                   49 
                   50 
                 
                 
                   
                     Zea mays 
                   
                   GRRP1 homolog 
                   51 
                   52 
                 
                 
                   
                     Oryza sativa 
                   
                   LNTP14 paralog 
                   53 
                   54 
                 
                 
                   
                     Zea mays 
                   
                   LNTP14 homolog 
                   55 
                   56 
                 
                 
                   
                     Oryza sativa 
                   
                   LNTP15 paralog 
                   57 
                   58 
                 
                 
                   
                     Oryza sativa 
                   
                   PTR11 paralog 
                   59 
                   60 
                 
                 
                   
                     Zea mays 
                   
                   PTR11 homolog 
                   61 
                   62 
                 
                 
                     
                 
              
             
           
         
       
     
    
    
     DETAILED DESCRIPTION 
     The disclosure of each reference set forth herein is hereby incorporated by reference in its entirety. 
     As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a plant” includes a plurality of such plants; reference to “a cell” includes one or more cells and equivalents thereof known to those skilled in the art, and so forth. 
     Definitions 
     As used herein, “increased nitrogen stress tolerance” of a plant refers to any measurable improvement in a physiological or physical characteristic, such as yield, as measured relative to a reference or control plant, when grown under low nitrogen and/or nitrogen limiting conditions. Typically, when a plant comprising a recombinant DNA construct or DNA modification in its genome exhibits increased nitrogen stress tolerance or NUE relative to a reference or control plant, the reference or control plant does not comprise in its genome the recombinant DNA construct or DNA modification. 
     As used herein “nitrogen use efficiency (NUE)” refers to the ratio between the amount of fertilizer N removed by a plant and the amount of fertilizer N applied. Accordingly, in certain embodiments an increase in N use efficiency refers to any detectable increase in the ratio between the amount of fertilizer N removed by a plant and the amount of fertilizer N applied. A person of ordinary skill in the art can calculate N use efficiency using routine methods in the art. 
     “Increased chlorate sensitivity” of a plant is measured relative to a reference or control plant and reflects ability of the plant to survive with less damage than a reference or control plant after treated with chlorate solution. In general, chlorate sensitivity can be used as a marker of abiotic stress tolerance, such as NUE. 
     “Agronomic characteristic” is a measurable parameter including but not limited to: greenness, grain yield, growth rate, total biomass or rate of accumulation, fresh weight at maturation, dry weight at maturation, fruit yield, seed yield, total plant nitrogen content, fruit nitrogen content, seed nitrogen content, nitrogen content in a vegetative tissue, total plant free amino acid content, fruit free amino acid content, seed free amino acid content, free amino acid content in a vegetative tissue, total plant protein content, fruit protein content, seed protein content, protein content in a vegetative tissue, drought tolerance, nitrogen uptake, root lodging, harvest index, stalk lodging, plant height, ear height, ear length, salt tolerance, tiller number, panicle size, early seedling vigor and seedling emergence under low temperature stress. 
     “Transgenic” refers to any cell, cell line, callus, tissue, plant part or plant, the genome of which has been altered by the presence of a heterologous nucleic acid, such as a recombinant DNA construct, including those initial transgenic events as well as those created by sexual crosses or asexual propagation from the initial transgenic event. The term “transgenic” 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. 
     A “control”, “control plant” or “control plant cell” or the like provides a reference point for measuring changes in phenotype of a subject plant or plant cell in which genetic alteration, such as transformation, has been affected as to a gene of interest. For example, a control plant may be a plant having the same genetic background as the subject plant except for the genetic alteration that resulted in the subject plant or cell. 
     “Plant” includes reference to whole plants, plant organs, plant tissues, seeds and plant cells and progeny of the same. Plant cells include, without limitation, cells from seeds, suspension cultures, embryos, meristematic regions, callus tissues, leaves, roots, shoots, gametophytes, sporophytes, pollen, and microspores. 
     “Progeny” comprises any subsequent generation of a plant. 
     “Modified plant” includes reference to a plant which comprises within its genome a heterologous polynucleotide or modified gene or promoter. For example, 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 DNA construct. 
     “Heterologous” with respect to sequence means a sequence 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. 
     “Polynucleotide”, “nucleic acid sequence”, “nucleotide sequence”, and “nucleic acid fragment” are used interchangeably and refer to a polymer of RNA or DNA that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases. Nucleotides (usually found in their 5′-monophosphate form) are referred to by their single-letter designation as follows: “A” for adenylate or deoxyadenylate, “C” for cytidylate or deoxycytidylate, and “G” for guanylate or deoxyguanylate for RNA or DNA, respectively; “U” for uridylate; “T” for deoxythymidylate; “R” for purines (A or G); “Y” for pyrimidines (C or T); “K” for G or T; “H” for A or C or T; “I” for inosine; and “N” for any nucleotide. 
     “Polypeptide”, “peptide”, “amino acid sequence” 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. The terms “polypeptide”, “peptide”, “amino acid sequence”, and “protein” are also inclusive of modifications including, but not limited to, glycosylation, lipid attachment, and sulfation, gamma-carboxylation of glutamic acid residues, hydroxylation and ADP-ribosylation. 
     “Recombinant DNA construct” refers to a combination of nucleic acid fragments that are not normally found together in nature. Accordingly, a recombinant DNA construct may comprise regulatory elements and coding sequences that are derived from different sources, or regulatory elements and coding sequences derived from the same source, but arranged in a manner different than that normally found in nature. 
     “Regulatory elements” refer to nucleotide sequences located upstream (5′ non-coding sequences), within, or downstream (3′ non-coding sequences) of a coding sequence, and influencing the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory elements may include, but are not limited to, promoters, translation leader sequences, introns, and poly-adenylation recognition sequences. The terms “regulatory sequence” and “regulatory element” and “regulatory region” are used interchangeably herein. 
     “Promoter” refers to a nucleic acid fragment capable of controlling transcription of another nucleic acid fragment. “Promoter functional in a plant” is a promoter capable of controlling transcription of genes in plant cells whether its origin is from a plant cell or not. “Tissue-specific promoter” and “tissue-preferred promoter” refers to a promoter that is expressed predominantly but not necessarily exclusively in one tissue or organ, but that may also be expressed in one specific cell or cell type. “Developmentally regulated promoter” is a promoter whose activity is determined by developmental events. 
     “Operably linked” refers to the association of nucleic acid fragments in a single fragment so that the function of one is regulated by the other. For example, a promoter is operably linked with a nucleic acid fragment when it is capable of regulating the transcription of that nucleic acid fragment. 
     “Expression” refers to the production of a functional product. For example, expression of a nucleic acid fragment may refer to transcription of the nucleic acid fragment (e.g., transcription resulting in mRNA or functional RNA) and/or translation of mRNA into a precursor or mature protein. 
     As used herein “increased”, “increase”, or the like refers to any detectable increase in an experimental group (e.g., plant with a DNA modification described herein) as compared to a control group (e.g., wild-type plant that does not comprise the DNA modification). Accordingly, increased expression of a protein comprises any detectable increase in the total level of the protein in a sample and can be determined using routine methods in the art such as, for example, Western blotting and ELISA. 
     As used herein, “yield” refers to the amount of agricultural production harvested per unit of land, and may include reference to bushels per acre or kilograms per mu of a crop at harvest, as adjusted for grain moisture (e.g., typically 15% for maize, 13.5% for rice). 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 or grams per plant, adjusted for grain moisture level at harvest. 
     As used herein, “sequence identity” or “identity” in the context of two polynucleotides or polypeptide sequences refer to the residues in the two sequences that 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. When sequences differ in conservative substitutions, the percent sequence identity may be adjusted upwards to correct for the conservative nature of the substitution. Sequences that 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., as implemented in the program PC/GENE (Intelligenetics, Mountain View, Calif.). 
     As used herein, “percentage of sequence identity” 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. 
     Unless stated otherwise, multiple alignments of the sequences provided herein are performed using the Clustal V method of alignment (Higgins and Sharp. (1989)  CABIOS.  5:151-153) with the default parameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwise alignments and calculation of percent identity of amino acid sequences using the Clustal V method are KTUPLE=1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. For nucleic acids these parameters are KTUPLE=2, GAP PENALTY=5, WINDOW=4 and DIAGONALS SAVED=4. After alignment of the sequences, using the Clustal V program, it is possible to obtain “percent identity” and “divergence” values by viewing the “sequence distances” table on the same program; unless stated otherwise, percent identities and divergences provided and claimed herein were calculated in this manner. 
     Compositions 
     A. Polynucleotides and Polypeptides 
     The present disclosure provides polynucleotides encoding the following polypeptides: 
     One aspect of the disclosure provides a polynucleotide encoding a polypeptide comprising an amino acid sequence that is at least 80% identical (e.g. 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%) to the amino acid sequence of any one of SEQ ID NO: 3 (OsLNTP12), SEQ ID NO: 6 (OsLNTP13), SEQ ID NO: 9 (OsGRRP1), SEQ ID NO: 12 (OsLNTP14), SEQ ID NO: 15 (OsLNTP15), SEQ ID NO: 18 (OsLNTP16), SEQ ID NO: 21 (OsLNTP17) and SEQ ID NO: 24 (OsPTR11). 
     “OsLNTP12” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP12 polypeptide (SEQ ID NO: 3) is encoded by the coding sequence (CDS) (SEQ ID NO: 2) or nucleotide sequence (SEQ ID NO: 1) at rice gene locus LOC_Os01g16280.1, which is annotated as “Expressed protein” in TIGR. “LNTP12 polypeptide” refers herein to the OsLNTP12 polypeptide and its paralogs (e.g., SEQ ID NO: 48 encoded by SEQ ID NO: 47) or homologs from other organisms. 
     “OsLNTP13” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP13 polypeptide (SEQ ID NO: 6) is encoded by the coding sequence (CDS) (SEQ ID NO: 5) or nucleotide sequence (SEQ ID NO: 4) at rice gene locus LOC_Os09g29880.1, which is annotated as “Expressed protein” in TIGR. “LNTP13 polypeptide” refers herein to the OsLNTP13 polypeptide and its paralogs (e.g., SEQ ID NO: 50 encoded by SEQ ID NO: 49) or homologs from other organisms. 
     “OsGRRP1” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsGRRP1 polypeptide (SEQ ID NO: 9) is encoded by the coding sequence (CDS) (SEQ ID NO: 8) or nucleotide sequence (SEQ ID NO: 7) at rice gene locus LOC_Os09g32320.1, which is annotated as “Expressed protein” in TIGR. “GRRP1 polypeptide” refers herein to the OsGRRP1 polypeptide and its paralogs or homologs from other organisms, such as maize (e.g., SEQ ID NO: 52 encoded by SEQ ID NO: 51). 
     “OsLNTP14” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP14 polypeptide (SEQ ID NO: 12) is encoded by the coding sequence (CDS) (SEQ ID NO: 11) or nucleotide sequence (SEQ ID NO: 10) at rice gene locus LOC_Os11g33380.1, which is annotated as “Expressed protein” in TIGR. “LNTP14 polypeptide” refers herein to the OsLNTP14 polypeptide and its paralogs (e.g., SEQ ID NO: 54 encoded by SEQ ID NO: 53) or homologs from other organisms, such as maize (e.g., SEQ ID NO: 56 encoded by SEQ ID NO: 55). 
     “OsLNTP15” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP15 polypeptide (SEQ ID NO: 15) is encoded by the coding sequence (CDS) (SEQ ID NO: 14) or nucleotide sequence (SEQ ID NO: 13) at rice gene locus LOC_Os09g32310.1, which is annotated as “Expressed protein” in TIGR. “LNTP15 polypeptide” refers herein to the OsLNTP15 polypeptide and its paralogs (e.g., SEQ ID NO: 58 encoded by SEQ ID NO: 57) or homologs from other organisms. 
     “OsLNTP16” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP16 polypeptide (SEQ ID NO: 18) is encoded by the coding sequence (CDS) (SEQ ID NO: 17) or nucleotide sequence (SEQ ID NO: 16) at rice gene locus LOC_Os04g32004.1, which is annotated as “Expressed protein” in TIGR. “LNTP16 polypeptide” refers herein to the OsLNTP16 polypeptide and its paralogs or homologs from other organisms. 
     “OsLNTP17” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsLNTP17 polypeptide (SEQ ID NO: 21) is encoded by the coding sequence (CDS) (SEQ ID NO: 20) or nucleotide sequence (SEQ ID NO: 19) at rice gene locus LOC_Os02g46530.1, which is annotated as “Expressed protein” in TIGR. “LNTP17 polypeptide” refers herein to the OsLNTP17 polypeptide and its paralogs or homologs from other organisms. 
     “OsPTR11” refers to a rice polypeptide that confers a low nitrogen tolerance phenotype when overexpressed. The OsPTR11 polypeptide (SEQ ID NO: 24) is encoded by the coding sequence (CDS) (SEQ ID NO: 23) or nucleotide sequence (SEQ ID NO: 22) at rice gene locus LOC_Os10g02340.1, which is annotated as “Expressed protein” in TIGR. “PTR11 polypeptide” refers herein to the OsPTR11 polypeptide and its paralogs (e.g., SEQ ID NO: 60 encoded by SEQ ID NO: 59) or homologs from other organisms, such as maize (e.g., SEQ ID NO: 62 encoded by SEQ ID NO: 61). 
     It is understood, as those skilled in the art will appreciate, that the disclosure encompasses more than the specific exemplary sequences. Alterations in a nucleic acid fragment which result in the production of a chemically equivalent amino acid at a given site, but do not affect the functional properties of the encoded polypeptide, are well known in the art. For example, a codon for the amino acid alanine, a hydrophobic amino acid, may be substituted by a codon encoding another less hydrophobic residue, such as glycine, or a more hydrophobic residue, such as valine, leucine, or isoleucine. Similarly, changes which result in substitution of one negatively charged residue for another, such as aspartic acid for glutamic acid, or one positively charged residue for another, such as lysine for arginine, can also be expected to produce a functionally equivalent product. Nucleotide changes which result in alteration of the N-terminal and C-terminal portions of the polypeptide molecule would also not be expected to alter the activity of the polypeptide. Each of the proposed modifications is well within the routine skill in the art, as is determination of retention of biological activity of the encoded products. 
     B. Recombinant DNA Constructs 
     Also provided are recombinant DNA constructs comprising any of the polynucleotides described herein. In certain embodiments, the recombinant DNA construct further comprises at least one regulatory element. In certain embodiments the at least one regulatory element is a heterologous regulatory element. In certain embodiments, the at least one regulatory element of the recombinant DNA construct comprises a promoter. In certain embodiments, the promoter is a heterologous promoter. 
     A number of promoters can be used in the recombinant DNA constructs of the present disclosure. The promoters can be selected based on the desired outcome, and may include constitutive, tissue-specific, inducible, or other promoters for expression in the host organism. 
     A “constitutive” promoter is a promoter, which is active under most environmental conditions. Constitutive promoters include, for example, the core promoter of the Rsyn7 promoter and other constitutive promoters disclosed in WO 99/43838 and U.S. Pat. No. 6,072,050; the core CaMV 35S promoter (Odell et al. (1985) Nature 313:810-812); rice actin (McElroy et al. (1990) Plant Cell 2:163-171); ubiquitin (Christensen et al. (1989) Plant Mol. Biol. 12:619-632 and Christensen et al. (1992) Plant Mol. Biol. 18:675-689); pEMU (Last et al. (1991) Theor. Appl. Genet. 81:581-588); MAS (Velten et al. (1984) EMBO J. 3:2723-2730); ALS promoter (U.S. Pat. No. 5,659,026), and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142; and 6,177,611. 
     A tissue-specific or developmentally-regulated promoter is a DNA sequence which regulates the expression of a DNA sequence selectively in the cells/tissues of a plant, such as in those cells/tissues critical to tassel development, seed set, or both, and which usually limits the expression of such a DNA sequence to the developmental period of interest (e.g. tassel development or seed maturation) in the plant. Any identifiable promoter which causes the desired temporal and spatial expression may be used in the methods of the present disclosure. 
     Many leaf-preferred promoters are known in the art (Yamamoto et al. (1997)  Plant J.  12 (2):255-265; Kwon et al. (1994)  Plant Physiol.  105:357-367; Yamamoto et al. (1994)  Plant Cell Physiol.  35 (5):773-778; Gotor et al. (1993)  Plant J.  3:509-518; Orozco et al. (1993)  Plant Mol. Biol.  23 (6):1129-1138; and Matsuoka et al. (1993)  Proc. Natl. Acad. Sci. USA  90 (20):9586-9590). 
     Promoters which are seed or embryo-specific and may be useful in the disclosure include soybean Kunitz trypsin inhibitor (Kti3, Jofuku and Goldberg. (1989)  Plant Cell  1:1079-1093), convicilin, vicilin, and legumin (Pea cotyledons) (Rerie, W. G., et al. (1991)  Mol. Gen. Genet.  259:149-157; Newbigin, E. J., et al. (1990)  Planta  180:461-470; Higgins, T. J. V., et al. (1988)  Plant. Mol. Biol.  11:683-695), zein (maize endosperm) (Schemthaner, J. P., et al. (1988)  EMBO J.  7:1249-1255), phaseolin (bean cotyledon) (Segupta-Gopalan, C., et al. (1985)  Proc. Natl. Acad. Sci.  82:3320-3324), phytohemagglutinin (bean cotyledon) (Voelker, T. et al. (1987)  EMBO J.  6:3571-3577), B-conglycinin and glycinin (soybean cotyledon) (Chen, Z-L, et al. (1988)  EMBO J.  7:297-302), glutelin (rice endosperm), hordein (barley endosperm) (Marris, C., et al. (1988)  Plant Mol. Biol.  10:359-366), glutenin and gliadin (wheat endosperm) (Colot, V., et al. (1987)  EMBO J.  6:3559-3564). Promoters of seed-specific genes operably linked to heterologous coding regions in chimeric gene constructions maintain their temporal and spatial expression pattern in transgenic plants. Such examples include  Arabidopsis  2S seed storage protein gene promoter to express enkephalin peptides in  Arabidopsis  and  Brassica napus  seeds (Vanderkerckhove et al. (1989)  Bio/Technology  7: L929-932), bean lectin and bean beta-phaseolin promoters to express luciferase (Riggs et al. (1989)  Plant Sci.  63:47-57), and wheat glutenin promoters to express chloramphenicol acetyl transferase (Colot et al. (1987)  EMBO J  6:3559-3564). 
     Inducible promoters selectively express an operably linked DNA sequence in response to the presence of an endogenous or exogenous stimulus, for example by chemical compounds (chemical inducers) or in response to environmental, hormonal, chemical, and/or developmental signals. Inducible or regulated promoters include, for example, promoters regulated by light, heat, stress, flooding or drought, phytohormones, wounding, or chemicals such as ethanol, jasmonate, salicylic acid, or safeners. 
     Also contemplated are synthetic promoters which include a combination of one or more heterologous regulatory elements. 
     The promoter of the recombinant DNA constructs of the invention can be any type or class of promoter known in the art, such that any one of a number of promoters can be used to express the various polynucleotide sequences disclosed herein, including the native promoter of the polynucleotide sequence of interest. The promoters for use in the recombinant DNA constructs of the invention can be selected based on the desired outcome. 
     The recombinant DNA constructs of the present disclosure may also include other regulatory elements, including but not limited to, translation leader sequences, introns, and polyadenylation recognition sequences. In certain embodiments, a recombinant DNA construct further comprises an enhancer or silencer. 
     An intron sequence can be added to the 5′ untranslated region, the protein-coding region or the 3′ untranslated region 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.  1:1183-1200). 
     C. Plants and Plant Cells 
     Provided are plants, plant cells, plant parts, seed and grain comprising in its genome any of the recombinant DNA constructs described herein, so that the plants, plant cells, plant parts, seed, and/or grain have increased expression of the encoded polypeptide. 
     Also provided are plants, plant cells, plant parts, seeds, and grain comprising an introduced genetic modification at a genomic locus that encodes a polypeptide comprising an amino acid sequence that is at least 80% identical to an amino acid sequence selected from the group consisting of SEQ ID NOs: 3, 6, 9, 12, 15, 18, 21 or 24. In certain embodiments, the genetic modification increases the activity of the encoded polypeptide. In certain embodiments, the genetic modification increases the level of the encoded polypeptide. In certain embodiments, the genetic modification increases both the level and activity of the encoded polypeptide. 
     The plant may be a monocotyledonous or dicotyledonous plant, for example, a rice or maize or soybean plant, such as a maize hybrid plant or a maize inbred plant. The plant may also be sunflower, sorghum, canola, wheat, alfalfa, cotton, barley, millet, sugar cane or switchgrass. 
     In certain embodiments the plant exhibits increased nitrogen stress tolerance when compared to a control plant. In certain embodiments, the plant exhibits an alteration of at least one agronomic characteristic when compared to the control plant. 
     One of ordinary skill in the art is familiar with protocols for simulating low nitrogen conditions and for evaluating nitrogen stress tolerance of plants that have been subjected to simulated or naturally-occurring nitrogen stress conditions. 
     D. Stacking With Other Traits of Interest 
     In some embodiments, the inventive polynucleotides disclosed herein are engineered into a molecular stack. Thus, the various host cells, plants, plant cells, plant parts, seeds, and/or grain disclosed herein can further comprise one or more traits of interest. In certain embodiments, the host cell, plant, plant part, plant cell, seed, and/or grain is stacked with any combination of polynucleotide sequences of interest in order to create plants with a desired combination of traits. As used herein, the term “stacked” refers to having multiple traits present in the same plant or organism of interest. For example, “stacked traits” may comprise a molecular stack where the sequences are physically adjacent to each other. A trait, as used herein, refers to the phenotype derived from a particular sequence or groups of sequences. In one embodiment, the molecular stack comprises at least one polynucleotide that confers tolerance to glyphosate. Polynucleotides that confer glyphosate tolerance are known in the art. 
     In certain embodiments, the molecular stack comprises at least one polynucleotide that confers tolerance to glyphosate and at least one additional polynucleotide that confers tolerance to a second herbicide. 
     In certain embodiments, the plant, plant cell, seed, and/or grain having an inventive polynucleotide sequence may be stacked with, for example, one or more sequences that confer tolerance to: an ALS inhibitor; an HPPD inhibitor; 2,4-D; other phenoxy auxin herbicides; aryloxyphenoxypropionate herbicides; dicamba; glufosinate herbicides; herbicides which target the protox enzyme (also referred to as “protox inhibitors”). 
     The plant, plant cell, plant part, seed, and/or grain having an inventive polynucleotide sequence can also be combined with at least one other trait to produce plants that further comprise a variety of desired trait combinations. For instance, the plant, plant cell, plant part, seed, and/or grain having an inventive polynucleotide sequence may be stacked with polynucleotides encoding polypeptides having pesticidal and/or insecticidal activity, or a plant, plant cell, plant part, seed, and/or grain having an inventive polynucleotide sequence may be combined with a plant disease resistance gene. 
     These stacked combinations can be created by any method including, but not limited to, breeding plants by any conventional methodology, or genetic transformation. If the sequences are stacked by genetically transforming the plants, the polynucleotide sequences of interest can be combined at any time and in any order. The traits can be introduced simultaneously in a co-transformation protocol with the polynucleotides of interest provided by any combination of transformation cassettes. For example, if two sequences will be introduced, the two sequences can be contained in separate transformation cassettes (trans) or contained on the same transformation cassette (cis). Expression of the sequences can be driven by the same promoter or by different promoters. In certain cases, it may be desirable to introduce a transformation cassette that will suppress the expression of the polynucleotide of interest. This may be combined with any combination of other suppression cassettes or overexpression cassettes to generate the desired combination of traits in the plant. It is further recognized that polynucleotide sequences can be stacked at a desired genomic location using a site-specific recombination system. See, for example, WO99/25821, WO99/25854, WO99/25840, WO99/25855, and WO99/25853, all of which are herein incorporated by reference. 
     Methods 
     Provided is a method for increasing nitrogen stress tolerance and/or grain yield in a plant, comprising increasing the expression of at least one polynucleotide encoding a polypeptide with amino acid sequence of at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%) sequence identity to SEQ ID NO: 3, 6, 9, 12, 15, 18, 21 or 24. 
     In certain embodiments, the method comprises: (a) expressing in a regenerable plant cell a recombinant DNA construct comprising a regulatory element operably linked to the polynucleotide encoding the polypeptide; and (b) generating the plant, wherein the plant comprises in its genome the recombinant DNA construct. In certain embodiments the regulatory element is a heterologous promoter. 
     In certain embodiments, the method comprises: (a) introducing in a regenerable plant cell a targeted genetic modification at a genomic locus that encodes the polypeptide; and (b) generating the plant, wherein the level and/or activity of the encoded polypeptide is increased in the plant. In certain embodiments the targeted genetic modification is introduced using a genome modification technique selected from the group consisting of a polynucleotide-guided endonuclease, CRISPR-Cas endonucleases, base editing deaminases, a zinc finger nuclease, a transcription activator-like effector nuclease (TALEN), engineered site-specific meganucleases, or Argonaute. In certain embodiments, the targeted genetic modification is present in (a) the coding region; (b) a non-coding region; (c) a regulatory sequence; (d) an untranslated region; or (e) any combination of (a)-(d) of the genomic locus that encodes a polypeptide comprising an amino acid sequence that is at least 80% identical to an amino acid sequence selected from the group consisting of SEQ ID NOs: 3, 6, 9, 12, 15, 18, 21 or 24. 
     In certain embodiments the DNA modification is an insertion of one or more nucleotides, preferably contiguous, in the genomic locus. For example, the insertion of an expression modulating element (EME), such as an EME described in PCT/US2018/025446, in operable linkage with the gene. In certain embodiments, the targeted DNA modification may be the replacement of the endogenous polypeptide promoter with another promoter known in the art to have higher expression. In certain embodiments, the targeted DNA modification may be the insertion of a promoter known in the art to have higher expression into the 5′UTR so that expression of the endogenous polypeptide is controlled by the inserted promoter. In certain embodiments, the DNA modification is a modification to optimize Kozak context to increase expression. In certain embodiments, the DNA modification is a polynucleotide modification or SNP at a site that regulates the stability of the expressed protein. 
     The plant for use in the inventive methods can be any plant species described herein. In certain embodiments, the plant is maize, soybean, or rice. 
     Various methods can be used to introduce a sequence of interest into a plant, plant part, plant cell, seed, and/or grain. “Introducing” is intended to mean presenting to the plant, plant cell, seed, and/or grain the inventive polynucleotide or resulting polypeptide in such a manner that the sequence gains access to the interior of a cell of the plant. The methods of the disclosure do not depend on a particular method for introducing a sequence into a plant, plant cell, seed, and/or grain, only that the polynucleotide or polypeptide gains access to the interior of at least one cell of the plant. 
     Transformation protocols as well as protocols for introducing polypeptides or polynucleotide sequences into plants may vary depending on the type of plant or plant cell, i.e., monocot or dicot, targeted for transformation. Suitable methods of introducing polypeptides and polynucleotides into plant cells include microinjection (Crossway et al. (1986)  Biotechniques  4:320-334), electroporation (Riggs et al. (1986)  Proc. Natl. Acad. Sci. USA  83:5602-5606,  Agrobacterium -mediated transformation (U.S. Pat. Nos. 5,563,055 and 5,981,840), direct gene transfer (Paszkowski et al. (1984)  EMBO J.  3:2717-2722), and ballistic particle acceleration (see, for example, U.S. Pat. Nos. 4,945,050; 5,879,918; 5,886,244; and, 5,932,782; Tomes et al. (1995) in  Plant Cell, Tissue, and Organ Culture: Fundamental Methods,  ed. Gamborg and Phillips (Springer-Verlag, Berlin); McCabe et al. (1988)  Biotechnology  6:923-926); and Lec1 transformation (WO 00/28058). Also see 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); McCabe et al. (1988)  Bio/Technology  6:923-926 (soybean); Finer and McMullen (1991)  In Vitro Cell Dev. Biol.  27P:175-182 (soybean); Singh et al. (1998)  Theor. Appl. Genet.  96:319-324 (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); U.S. Pat. Nos. 5,240,855; 5,322,783; and, 5,324,646; Klein et al. (1988)  Plant Physiol.  91:440-444 (maize); Fromm et al. (1990)  Biotechnology  8:833-839 (maize); Hooykaas-Van Slogteren et al. (1984)  Nature  ( London ) 311:763-764; U.S. Pat. No. 5,736,369 (cereals); Bytebier 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. Chapman et al. (Longman, New York), pp. 197-209 (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); 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 Biotechnology  14:745-750 (maize via  Agrobacterium tumefaciens ); all of which are herein incorporated by reference. 
     In other embodiments, the inventive polynucleotides disclosed herein may be introduced into plants by contacting plants with a virus or viral nucleic acids. Generally, such methods involve incorporating a nucleotide construct of the disclosure within a DNA or RNA molecule. It is recognized that the inventive polynucleotide sequence may be initially synthesized as part of a viral polyprotein, which later may be processed by proteolysis in vivo or in vitro to produce the desired recombinant protein. Further, it is recognized that promoters disclosed herein also encompass promoters utilized for transcription by viral RNA polymerases. Methods for introducing polynucleotides into plants and expressing a protein encoded therein, involving viral DNA or RNA molecules, are known in the art. See, for example, U.S. Pat. Nos. 5,889,191, 5,889,190, 5,866,785, 5,589,367, 5,316,931, and Porta et al. (1996)  Molecular Biotechnology  5:209-221; herein incorporated by reference. 
     The cells that have been transformed may be grown into plants in accordance with conventional ways. See, for example, McCormick et al. (1986)  Plant Cell Reports  5:81-84. These plants may then be grown, and either pollinated with the same transformed strain or different strains, and the resulting progeny having constitutive expression of the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that expression of the desired phenotypic characteristic is stably maintained and inherited and then seeds harvested to ensure expression of the desired phenotypic characteristic has been achieved. In this manner, the present disclosure provides transformed seed (also referred to as “transgenic seed”) having a polynucleotide disclosed herein, for example, as part of an expression cassette, stably incorporated into their genome. 
     Transformed plant cells which are derived by plant transformation techniques, including those discussed above, can be cultured to regenerate a whole plant which possesses the transformed genotype (i.e., an inventive polynucleotide), and thus the desired phenotype, such as increased yield. For transformation and regeneration of maize see, Gordon-Kamm et al.,  The Plant Cell,  2:603-618 (1990). 
     Various methods can be used to introduce a genetic modification at a genomic locus that encodes a polypeptide disclosed herein into the plant, plant part, plant cell, seed, and/or grain. In certain embodiments the targeted DNA modification is through a genome modification technique selected from the group consisting of a polynucleotide-guided endonuclease, CRISPR-Cas endonucleases, base editing deaminases, zinc finger nuclease, a transcription activator-like effector nuclease (TALEN), engineered site-specific meganuclease, or Argonaute. 
     In some embodiments, the genome modification may be facilitated through the induction of a double-stranded break (DSB) or single-strand break, in a defined position in the genome near the desired alteration. DSBs can be induced using any DSB-inducing agent available, including, but not limited to, TALENs, meganucleases, zinc finger nucleases, Cas9-gRNA systems (based on bacterial CRISPR-Cas systems), guided cpf1 endonuclease systems, and the like. In some embodiments, the introduction of a DSB can be combined with the introduction of a polynucleotide modification template. 
     A polynucleotide modification template can be introduced into a cell by any method known in the art, such as, but not limited to, transient introduction methods, transfection, electroporation, microinjection, particle mediated delivery, topical application, whiskers mediated delivery, delivery via cell-penetrating peptides, or mesoporous silica nanoparticle (MSN)-mediated direct delivery. 
     The polynucleotide modification template can be introduced into a cell as a single stranded polynucleotide molecule, a double stranded polynucleotide molecule, or as part of a circular DNA (vector DNA). The polynucleotide modification template can also be tethered to the guide RNA and/or the Cas endonuclease. 
     A “modified nucleotide” or “edited nucleotide” refers to a nucleotide sequence of interest that comprises at least one alteration when compared to its non-modified nucleotide sequence. Such “alterations” include, for example: (i) replacement of at least one nucleotide, (ii) a deletion of at least one nucleotide, (iii) an insertion of at least one nucleotide, or (iv) any combination of (i)-(iii). 
     The term “polynucleotide modification template” includes a polynucleotide that comprises at least one nucleotide modification when compared to the nucleotide sequence to be edited. A nucleotide modification can be at least one nucleotide substitution, addition or deletion. Optionally, the polynucleotide modification template can further comprise homologous nucleotide sequences flanking the at least one nucleotide modification, wherein the flanking homologous nucleotide sequences provide sufficient homology to the desired nucleotide sequence to be edited. 
     The process for editing a genomic sequence combining DSB and modification templates generally comprises: providing to a host cell, a DSB-inducing agent, or a nucleic acid encoding a DSB-inducing agent, that recognizes a target sequence in the chromosomal sequence and is able to induce a DSB in the genomic sequence, and at least one polynucleotide modification template comprising at least one nucleotide alteration when compared to the nucleotide sequence to be edited. The polynucleotide modification template can further comprise nucleotide sequences flanking the at least one nucleotide alteration, in which the flanking sequences are substantially homologous to the chromosomal region flanking the DSB. 
     The endonuclease can be provided to a cell by any method known in the art, for example, but not limited to, transient introduction methods, transfection, microinjection, and/or topical application or indirectly via recombination constructs. The endonuclease can be provided as a protein or as a guided polynucleotide complex directly to a cell or indirectly via recombination constructs. The endonuclease can be introduced into a cell transiently or can be incorporated into the genome of the host cell using any method known in the art. In the case of a CRISPR-Cas system, uptake of the endonuclease and/or the guided polynucleotide into the cell can be facilitated with a Cell Penetrating Peptide (CPP) as described in WO2016073433 published May 12, 2016. 
     In addition to modification by a double strand break technology, modification of one or more bases without such double strand break are achieved using base editing technology, see e.g., Gaudelli et al., (2017) Programmable base editing of A*T to G*C in genomic DNA without DNA cleavage. Nature 551 (7681):464-471; Komor et al., (2016) Programmable editing of a target base in genomic DNA without double-stranded DNA cleavage, Nature 533 (7603):420-4. 
     These fusions contain dCas9 or Cas9 nickase and a suitable deaminase, and they can convert e.g., cytosine to uracil without inducing double-strand break of the target DNA. Uracil is then converted to thymine through DNA replication or repair. Improved base editors that have targeting flexibility and specificity are used to edit endogenous locus to create target variations and improve grain yield. Similarly, adenine base editors enable adenine to inosine change, which is then converted to guanine through repair or replication. Thus, targeted base changes i.e., C⋅G to T⋅A conversion and A⋅T to G⋅C conversion at one more location made using appropriate site-specific base editors. 
     In an embodiment, base editing is a genome editing method that enables direct conversion of one base pair to another at a target genomic locus without requiring double-stranded DNA breaks (DSBs), homology-directed repair (HDR) processes, or external donor DNA templates. In an embodiment, base editors include (i) a catalytically impaired CRISPR-Cas9 mutant that are mutated such that one of their nuclease domains cannot make DSBs; (ii) a single-strand-specific cytidine/adenine deaminase that converts C to U or A to G within an appropriate nucleotide window in the single-stranded DNA bubble created by Cas9; (iii) a uracil glycosylase inhibitor (UGI) that impedes uracil excision and downstream processes that decrease base editing efficiency and product purity; and (iv) nickase activity to cleave the non-edited DNA strand, followed by cellular DNA repair processes to replace the G-containing DNA strand. 
     As used herein, a “genomic region” is a segment of a chromosome in the genome of a cell that is present on either side of the target site or, alternatively, also comprises a portion of the target site. The genomic region can comprise at least 5-10, 5-15, 5-20, 5-25, 5-30, 5-35, 5-40, 5-45, 5-50, 5-55, 5-60, 5-65, 5-70, 5-75, 5-80, 5-85, 5-90, 5-95, 5-100, 5-200, 5-300, 5-400, 5-500, 5-600, 5-700, 5-800, 5-900, 5-1000, 5-1100, 5-1200, 5-1300, 5-1400, 5-1500, 5-1600, 5-1700, 5-1800, 5-1900, 5-2000, 5-2100, 5-2200, 5-2300, 5-2400, 5-2500, 5-2600, 5-2700, 5-2800. 5-2900, 5-3000, 5-3100 or more bases such that the genomic region has sufficient homology to undergo homologous recombination with the corresponding region of homology. 
     TAL effector nucleases (TALEN) are a class of sequence-specific nucleases that can be used to make double-strand breaks at specific target sequences in the genome of a plant or other organism (Miller et al. (2011) Nature Biotechnology 29:143-148). 
     Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain. Endonucleases include restriction endonucleases, which cleave DNA at specific sites without damaging the bases, and meganucleases, also known as homing endonucleases (HEases), which like restriction endonucleases, bind and cut at a specific recognition site, however the recognition sites for meganucleases are typically longer, about 18 bp or more (patent application PCT/US12/30061, filed on Mar. 22, 2012). Meganucleases have been classified into four families based on conserved sequence motifs, the families are the LAGLIDADG, GIY-YIG, H-N-H, and His-Cys box families. These motifs participate in the coordination of metal ions and hydrolysis of phosphodiester bonds. HEases are notable for their long recognition sites, and for tolerating some sequence polymorphisms in their DNA substrates. The naming convention for meganuclease is similar to the convention for other restriction endonuclease. Meganucleases are also characterized by prefix F-, I-, or PI- for enzymes encoded by free-standing ORFs, introns, and inteins, respectively. One step in the recombination process involves polynucleotide cleavage at or near the recognition site. The cleaving activity can be used to produce a double-strand break. For reviews of site-specific recombinases and their recognition sites, see, Sauer (1994) Curr Op Biotechnol 5:521-7; and Sadowski (1993) FASEB 7:760-7. In some examples the recombinase is from the Integrase or Resolvase families. 
     Zinc finger nucleases (ZFNs) are engineered double-strand break inducing agents comprised of a zinc finger DNA binding domain and a double-strand-break-inducing agent domain. Recognition site specificity is conferred by the zinc finger domain, which typically comprising two, three, or four zinc fingers, for example having a C2H2 structure, however other zinc finger structures are known and have been engineered. Zinc finger domains are amenable for designing polypeptides which specifically bind a selected polynucleotide recognition sequence. ZFNs include an engineered DNA-binding zinc finger domain linked to a non-specific endonuclease domain, for example nuclease domain from a Type IIs endonuclease such as FokI. Additional functionalities can be fused to the zinc-finger binding domain, including transcriptional activator domains, transcription repressor domains, and methylases. In some examples, dimerization of nuclease domain is required for cleavage activity. Each zinc finger recognizes three consecutive base pairs in the target DNA. For example, a 3-finger domain recognized a sequence of 9 contiguous nucleotides, with a dimerization requirement of the nuclease, two sets of zinc finger triplets are used to bind an 18 nucleotide recognition sequence. 
     Genome editing using DSB-inducing agents, such as Cas9-gRNA complexes, has been described, for example in U.S. Patent Application US 2015-0082478 A1, published on Mar. 19, 2015, WO2015/026886 A1, published on Feb. 26, 2015, WO2016007347, published on Jan. 14, 2016, and WO201625131, published on Feb. 18, 2016, all of which are incorporated by reference herein. 
     EXAMPLES 
     The following are examples of specific embodiments of some aspects of the invention. The examples are offered for illustrative purposes only and are not intended to limit the scope of the invention in any way. 
     Example 1 
     Cloning and Vector Construction of Nitrogen Stress Tolerance Genes 
     A binary construct that contains four multimerized enhancers elements derived from the Cauliflower Mosaic Virus 35S (CaMV 35S) promoter was used, and the rice activation tagging population was developed from four japonica ( Oryza sativa  ssp.  Japonica ) varieties (Zhonghua 11, Chaoyou 1, Taizhong 65 and Nipponbare), which were transformed by the  Agrobacteria -mediated transformation method as described by Lin and Zhang ((2005)  Plant Cell Rep.  23:540-547). The transgenic lines generated were developed and the transgenic seeds were harvested to form the rice activation tagging population. 
     Nitrogen stress tolerance tagging lines (ATLs) were confirmed in repeated field experiments and their T-DNA insertion loci were determined. The genes near the left border and right border of the T-DNA were cloned and the functional genes were recapitulated by field screens. Only the recapitulated functional genes are showed herein. And based on LOC IDs of these genes shown in Table 2, primers were designed for cloning the rice nitrogen stress tolerance genes OsLNTP12, OsLNTP13, OsGRRP1, OsLNTP14, OsLNTP15, OsLNTP16, OsLNTP17, OsPTR11. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Rice gene names, Gene IDs (from TIGR) and Construct IDs 
               
            
           
           
               
               
               
               
            
               
                   
                 Gene name 
                 LOC ID 
                 Construct ID 
               
               
                   
                   
               
               
                   
                 OsLNTP12 
                 LOC_Os01g16280.1 
                 DP1002 
               
               
                   
                 OsLNTP13 
                 LOC_Os09g29880.1 
                 DP1554 
               
               
                   
                 OsGRRP1 
                 LOC_Os09g32320.1 
                 DP1227 
               
               
                   
                 OsLNTP14 
                 LOC_Os11g33380.1 
                 DP1167 
               
               
                   
                 OsLNTP15 
                 LOC_Os09g32310.1 
                 DP1226 
               
               
                   
                 OsLNTP16 
                 LOC_Os04g32004.1 
                 DP1833 
               
               
                   
                 OsLNTP17 
                 LOC_Os02g46530.1 
                 DP2194 
               
               
                   
                 OsPTR11 
                 LOC_Os10g02340.1 
                 DP0914 
               
               
                   
                   
               
            
           
         
       
     
     PCR amplified products were extracted after the agarose gel electrophoresis using a column kit and then ligated with TA cloning vectors. The sequences and orientation in these constructs were confirmed by sequencing. Each gene was cloned into a plant binary construct. 
     Example 2 
     Transformation and Gene Expression Analysis of Transgenic Rice Lines 
     Zhonghua 11 ( Oryza sativa  L.) were transformed with either a vector prepared in Example 1 or an empty vector (DP0158) by  Agrobacteria -mediated transformation as described by Lin and Zhang ((2005)  Plant Cell Rep.  23:540-547). Transgenic seedlings (T 0 ) generated in the transformation laboratory were transplanted in field to get T 1  seeds. The T 1  and subsequent T 2  seeds were screened to confirm transformation and positively identified transgenic seeds were used in the following trait screens. 
     The gene expression levels in the leaves of the transgenic rice plants were determined by RT-PCR. Primers were designed for the RT-PCR for OsLNTP12, OsLNTP15, and OsPTR11 genes in the over-expression transgenic rice. The level of expression in ZH11-TC (tissue cultured ZH11 rice) was set at 1.00, and the expression levels in the DP1002, DP1226 and DP0914-transgenic rice plants were compared to ZH11-TC. Gene expression was normalized based on the EF-1α mRNA levels, and the results from the gene expression analysis are provided in Table 3 below. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Relative Expression Level Fold Increase in Transgenic Rice Plants 
               
            
           
           
               
               
               
            
               
                 Gene name 
                 Construct ID 
                 Relative Expression Level Fold Increase 
               
               
                   
               
               
                 OsLNTP12 
                 DP1002 
                 From 1004.58 to 2328.36 
               
               
                 OsLNTP15 
                 DP1226 
                 From 2.18 to 7724.55 
               
               
                 OsPTR11 
                 DP0914 
                 From 159.35 to 1135.97 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Characterization of the Transgenic Rice Plants 
     The transgenic rice plants from Example 2 and ZH11-TC and DP0158 rice plants were tested for: (a) low nitrogen tolerance/nitrogen use efficiency, (b) cholate sensitivity. 
     T 2  seeds from the plants of Example 2 were sterilized by 800 ppm carbendazol for 8 hours at 32° C. and washed 3-5 time, soaked in water for 16 hours at 32° C., and germinated for 18 hours at 35-37° C. in an incubator. Germinated seeds were used as follows for each test: 
     (a) low nitrogen tolerance/nitrogen use efficiency—Two nitrogen levels: N-0 (using fertilizer without nitrogen) and N-1 (with normal fertilizer) were set in the experiment. Germinated seeds were planted in a seedbed field. At 3-leaf stage, the seedlings were transplanted into the testing field with 4 replicates and 10 plants per replicate for each transgenic line, and the 4 replicates were planted in the same block. The ZH11-TC and DP0158 plants were planted nearby the transgenic lines in the same block, and were used as controls in the statistical analysis. The rice plants were managed by normal practice using pesticides, but applying phosphorous fertilizer and potassium fertilizer for N-0 treatment and normal fertilizer for N-1 treatment. 
     At the end of the season, six representative plants of each transgenic line were harvested from the middle of the row per line and grain yield per plant was measured. The grain yield per plant data were statistically analyzed using mixed linear model by ASReml program. Positive transgenic lines are selected based on the analysis (P&lt;0.1). 
     (b) cholate sensitivity—this assay was performed in culture room kept temperature at 28-30° C. and humidity around ˜30%. The germinated seeds were placed in a tube with a hole at the bottom, and water cultured at 30 ° C. for 6 days till one-leaf and one-terminal bud stage. Uniform seedlings about 5.5 cm in height were selected for chlorate screening. Randomized block design was used in this experiment. There are five blocks in one screened container. Each transgenic line was placed in one row (12 plants/line), and ZH11-TC seedlings were placed in 3 rows (31*2 plants) randomly in one block. Then the seedlings were treated with 0.4 mM chlorate in concentration for 3-5 days at 10 h day/14 h night, the treated seedlings first encountered night and absorb the chlorate solution which was changed at the third day. After treated for 5 days, the seedlings were then cultured in 1/10 Hoagland&#39;s solution for 4 days. The seedlings with withered leaves and totally without green are counted as sensitive; while the seedlings only with necrosed leaves or stem, or bleached leaves are not considered to be sensitive seedlings. 
     Sensitive rate was used as a parameter to for this assay, which is the percentage of the number of sensitive plants over the total plant number. The data was analyzed using a statistic model of “Y˜seg+line (seg)+rep+error” with random effect of “rep” and Statistic Method of “SAS Proc Glimmix”. 
     The results from these studies are provided in Table 4, which provides the combined data of the transgenic lines for each of the constructs. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Agronomic Characteristics of the Transgenic Rice Plants 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Avg. yield per plant 
                 Avg. yield per plant 
                 Avg. 
               
               
                   
                   
                 under field low 
                 under field normal 
                 chlorate 
               
               
                   
                 Construct 
                 nitrogen conditions 
                 nitrogen conditions 
                 sensitive 
               
               
                 No 
                 ID 
                 (g/plant) 
                 (g/plant) 
                 rate (%) 
               
               
                   
               
               
                 1 
                 ZH11-TC 
                 20.48 ± 1.15 
                 28.50 ± 0.72 
                   
               
               
                   
                 DP0158 
                 22.20 ± 1.14 
                 31.02 ± 0.73 
               
               
                   
                 DP1002 
                     23.26 ± 1.14 a, b   
                      32.23 ± 0.73  a, b   
               
               
                 2 
                 ZH11-TC 
                 20.55 ± 1.04 
                 28.80 ± 0.86 
                 26% 
               
               
                   
                 DP0158 
                 22.13 ± 1.03 
                 31.14 ± 0.88 
                 29% 
               
               
                   
                 DP1554 
                      23.51 ± 1.02  a, b   
                      33.50 ± 0.86  a, b   
                      43%  m, n   
               
               
                 3 
                 ZH11-TC 
                 20.48 ± 1.14 
                 28.37 ± 0.67 
               
               
                   
                 DP0158 
                 22.09 ± 1.14 
                 30.23 ± 0.74 
               
               
                   
                 DP1227 
                      23.25 ± 1.14  a, b   
                      31.37 ± 0.69  a, b   
               
               
                 4 
                 ZH11-TC 
                 20.54 ± 0.84 
                 24.46 ± 0.97 
                 17% 
               
               
                   
                 DP0158 
                 19.57 ± 0.84 
                 22.21 ± 0.97 
                 37% 
               
               
                   
                 DP1167 
                      23.51 ± 1.41  a, b   
                      27.07 ± 1.66  a, b   
                      69%  m, n   
               
               
                 5 
                 ZH11-TC 
                 34.70 ± 2.46 
               
               
                   
                 DP0158 
                 31.12 ± 2.46 
               
               
                   
                 DP1226 
                     35.96 ± 1.93  b   
               
               
                 6 
                 ZH11-TC 
                 33.24 ± 2.36 
                 27.20 ± 0.68 
               
               
                   
                 DP0158 
                 31.34 ± 2.35 
                 24.90 ± 0.67 
               
               
                   
                 DP1833 
                     35.44 ± 1.86  b   
                     29.04 ± 1.52  b   
               
               
                 7 
                 ZH11-TC 
                 20.54 ± 0.84 
                 23.72 ± 0.94 
               
               
                   
                 DP0158 
                 19.57 ± 0.84 
                 22.19 ± 0.93 
               
               
                   
                 DP2194 
                 20.09 ± 1.26 
                      26.97 ± 1.56  a, b   
               
               
                 8 
                 ZH11-TC 
                 20.48 ± 1.14 
                 28.88 ± 0.85 
               
               
                   
                 DP0158 
                 22.09 ± 1.14 
                 30.75 ± 0.86 
               
               
                   
                 DP0914 
                     23.10 ± 1.16  a   
                      33.22 ± 0.83  a, b   
               
               
                   
               
               
                   a  P ≤ 0.1 compared to ZH11-TC control in field; 
               
               
                   b  P ≤ 0.1 compared to DP0158 control in field. 
               
               
                   m  P ≤ 0.05 compared to ZH11-TC control in Lab; 
               
               
                   n  P ≤ 0.05 compared to DP0158 control in Lab. 
               
            
           
         
       
     
     DP1002-transgenic rice plants were tested three times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in three years. Two of them consistently showed that the average yield per plant of DP1002-transgenic rice plants increased under field low nitrogen and normal nitrogen conditions. As shown in table 4, four lines were tested under field low nitrogen and normal nitrogen conditions. Under field low nitrogen conditions, 1 of 4 line showed significantly increased the yield than that of DP0158 control, and 4 of 4 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 4 lines is 14% and 5% higher than that of ZH11-TC and DP0158 controls, respectively. While, under field normal nitrogen conditions, 2 of 4 lines showed significantly increased the yield than that of DP0158 control, and 4 of 4 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 4 lines is 13% and 4% higher than that of ZH11-TC and DP0158 controls, respectively. These results show that OsLNTP12 transgenic rice may have increased low nitrogen tolerance and/or nitrogen use efficiency. 
     DP1554-transgenic rice plants were tested three times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in three years. Two of them consistently showed that the average yield per plant of DP1554-transgenic rice plants increased under field low nitrogen and normal nitrogen conditions. As shown in table 4, five lines were tested under field low nitrogen and normal nitrogen conditions. Under field low nitrogen conditions, 3 of 5 lines showed significantly increased the yield than that of DP0158 control, and 4 of 5 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 5 lines is 14% and 6% higher than that of ZH11-TC and DP0158 controls, respectively. While, under field normal nitrogen conditions, 3 of 5 lines showed significantly increased the yield than that of DP0158 control, and 4 of 5 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 5 lines is 16% and 8% higher than that of ZH11-TC and DP0158 controls, respectively. DP1554-transgenic rice plants were also tested two times in chlorate assays. Consistently results were obtained. In the first experiment, ten lines were tested, and the average chlorate sensitive rate of all DP1554-transgenic lines (43%) was significantly greater than that of ZH11-TC (26%) and DP0158 (29%) controls at construct level. At transgenic line level, 6 of 10 lines had significantly greater sensitive rates than that of ZH11-TC and DP0158 controls (Table 4). These results demonstrate that OsLNTP13 may increase the nitrogen use efficiency and/or low nitrogen tolerance of transgenic plants and increase the chlorate sensitivity of transgenic plants compared to both controls. 
     DP1227-transgenic rice plants were tested three times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in three years. All experiments consistently showed that the average yield per plant of DP1227-transgenic rice plants increased under field low nitrogen and field normal nitrogen conditions. As shown in table 4, under field low nitrogen conditions, 1 of 4 line showed significantly increased the yield than that of DP0158 control, and 2 of 4 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 4 lines is 14% and 5% higher than that of ZH11-TC and DP0158 controls, respectively. While, under field normal nitrogen conditions, 2 of 4 lines showed significantly increased the yield than that of DP0158 control, and 3 of 4 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 4 lines is 11% and 4% higher than that of ZH11-TC and DP0158 controls, respectively. These results demonstrate that OsGRRP1 may increase the nitrogen use efficiency and/or low nitrogen tolerance of transgenic rice plants compared to both controls. 
     DP1167-transgenic rice plants were tested two times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in two years. All experiments consistently showed that the average yield per plant of DP1167-transgenic rice plants increased under field low nitrogen and field normal nitrogen conditions. As shown in table 4, seven lines were tested under field low nitrogen and normal nitrogen conditions. Under field low nitrogen conditions, 7 of 7 lines showed significantly increased the yield than that of DP0158 control, and 3 of 7 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 7 lines is 14% and 20% higher than that of ZH11-TC and DP0158 controls, respectively. While, under field normal nitrogen conditions, 6 of 6 lines showed significantly increased the yield than that of DP0158 control, and 1 of 6 line showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 6 lines is 11% and 22% higher than that of ZH11-TC and DP0158 controls, respectively. DP1167-transgenic rice plants were also tested two times in chlorate assays. Consistently results were obtained. In the second experiment, the average chlorate sensitive rate of all DP1167-transgenic lines (69%) was significantly greater than that of ZH11-TC (17%) and DP0158 (37%) controls at construct level. At transgenic line level, all ten lines had significantly greater sensitive rates than that of ZH11-TC and DP0158 controls (Table 4). These results demonstrate that OsLNTP14 may increase the nitrogen use efficiency and/or low nitrogen tolerance of transgenic plants and increase the chlorate sensitivity of transgenic plants compared to both controls. 
     DP1226-transgenic rice plants were tested two times under field low nitrogen conditions in Beijing in two years. All experiments consistently showed that the average yield per plant of DP1226-transgenic rice plants increased under field low nitrogen conditions. As shown in table 4, under field low nitrogen conditions, 7 of 7 lines showed significantly increased the yield than that of DP0158 control. All lines also showed increased the yield than that of ZH11-TC control but not to a significant degree. The average yield per plant of these 7 lines is 4% and 16% higher than that of ZH11-TC and DP0158 controls, respectively. These results demonstrate that OsLNTP15 may increase the low nitrogen tolerance of transgenic plants compared to both controls. 
     DP1833-transgenic rice plants were tested two times under field low nitrogen conditions or field normal nitrogen conditions in Beijing in two years. Two of them consistently showed that the average yield per plant of DP1833-transgenic rice plants increased under field low nitrogen and field normal nitrogen conditions. As shown in table 4, eight lines were tested under field low nitrogen conditions, 6 of 8 lines showed significantly increased the yield than that of DP0158 control, and 7 of 8 lines showed increased the yield than that of ZH11-TC control but not to a significant degree. The average yield per plant of these 8 lines is 7% and 13% higher than that of ZH11-TC and DP0158 controls, respectively. In another year, seven lines were tested again under field normal nitrogen conditions, and 5 of 7 lines showed significantly increased the yield than that of DP0158 control, and 1 of 7 line showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 7 lines is 7% and 17% higher than that of ZH11-TC and DP0158 controls, respectively. These results show that OsLNTP16 transgenic rice may have increased low nitrogen tolerance and/or nitrogen use efficiency. 
     DP2194-transgenic rice plants were tested two times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in two years. Two of them consistently showed that the average yield per plant of DP2194-transgenic rice plants increased under field low nitrogen and normal nitrogen conditions. As shown in table 4, twelve lines were tested under field low nitrogen conditions, 3 of 12 lines showed increased the yield than that of ZH11-TC and DP0158 controls, but not to a significant degree. While, under field normal nitrogen conditions, and 6 of 7 lines showed significantly increased the yield than that of DP0158 control, and 3 of 7 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 7 lines is 14% and 22% higher than that of ZH11-TC and DP0158 controls, respectively. These results show that OsLNTP17transgenic rice may have increased nitrogen use efficiency under field normal nitrogen conditions. 
     DP0914-transgenic rice plants were tested three times under field low nitrogen conditions and/or field normal nitrogen conditions in Beijing in three years. Two of them consistently showed that the average yield per plant of DP0914-transgenic rice plants increased under field low nitrogen and normal nitrogen conditions. As shown in table 4, under the field low nitrogen conditions, 1 of 4 lines showed significantly increased yield than that of DP0158 control, and 4 of 4 lines showed significantly increased the yield than that of ZH11-TC control. The average yield per plant of these 4 lines is 13% and 5% higher than that of ZH11-TC and DP0158 controls, respectively. Under the field normal nitrogen conditions, 3 of 5 lines showed significantly increased yield than that of DP0158 control, and 5 of 5 lines showed significantly increased yield than that of ZH11-TC control. The average yield per plant of these 5 lines is 15% and 8% higher than that of ZH11-TC and DP0158 controls, respectively. These results show that OsPTR11 transgenic rice may have increased low nitrogen tolerance and/or nitrogen use efficiency. 
     Taken together, these results indicate that OsLNTP12, OsLNTP13, OsGRRP1, OsLNTP14, OsLNTP15, OsLNTP16, OsLNTP17 and OsPTR11-transgenic rice plants have increased low nitrogen tolerance and/or nitrogen use efficiency. 
     Example 4 
     Transformation and Evaluation of Maize with Rice Nitrogen Stress Tolerance Genes 
     Maize plants can be transformed one of the polynucleotides encoding the polypeptides described herein or a corresponding homolog from maize,  Arabidopsis,  or other species. Expression of the gene in the maize transformation vector can be under control of a constitutive promoter such as the maize ubiquitin promoter (Christensen et al. (1989)  Plant Mol. Biol.  12:619-632 and Christensen et al. (1992)  Plant Mol. Biol.  18:675-689) or under control of another promoter, such as a stress-responsive promoter or a tissue-preferred promoter. The recombinant DNA construct can be introduced into maize cells by particle bombardment substantially as described in International Patent Publication WO 2009/006276. Alternatively, maize plants can be transformed with the recombinant DNA construct by  Agrobacterium -mediated transformation substantially as described by Zhao et al. in  Meth. Mol. Biol.  318:315-323 (2006) and in Zhao et al.,  Mol. Breed.  8:323-333 (2001) and U.S. Pat. No. 5,981,840 issued Nov. 9, 1999. 
     Progeny of the regenerated plants, such as T 1  plants, can be subjected to a soil-based nitrogen stress. Using image analysis, plant area, volume, growth rate and color can be measured at multiple times before and during nitrogen stress. Significant delay in wilting or leaf area reduction, a reduced yellow-color accumulation, and/or an increased growth rate during nitrogen stress, relative to a control, will be considered evidence that the gene functions in maize to enhance nitrogen stress tolerance and/or NUE.