# Patent

## Title
Nucleotide sequences mediating male fertility and method of using same

## Abstract

Nucleotide sequences mediating male fertility in plants are described, with DNA molecule and amino acid sequences set forth. Promoter sequences and their essential regions are also identified. The nucleotide sequences are useful in mediating male fertility in plants.

## Background
This application is a continuation-in-part of previously filed and application U.S. Ser. No. 10/412,000 filed Apr. 11, 2003, now U.S. Pat. No. 7,151,205 which is a continuation of previously filed application U.S. Ser. No. 09/670,153, filed Sep. 26, 2000, now abandoned, both of which are incorporated by reference in their entirety.


BACKGROUND OF THE INVENTION
Development of hybrid plant breeding has made possible considerable advances in quality and quantity of crops produced. Increased yield and combination of desirable characteristics, such as resistance to disease and insects, heat and drought tolerance, along with variations in plant composition are all possible because of hybridization procedures. These procedures frequently rely heavily on providing for a male parent contributing pollen to a female parent to produce the resulting hybrid.
Field crops are bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinating if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant.
In Brassica, the plant is normally self sterile and can only be cross-pollinated. In self-pollinating species, such as soybeans and cotton, the male and female plants are anatomically juxtaposed. During natural pollination, the male reproductive organs of a given flower pollinate the female reproductive organs of the same flower.
Maize plants (Zea mays L.) present a unique situation in that they can be bred by both self-pollination and cross-pollination techniques. Maize has male flowers, located on the tassel, and female flowers, located on the ear, on the same plant. It can self or cross pollinate. Natural pollination occurs in maize when wind blows pollen from the tassels to the silks that protrude from the tops of the incipient ears.
A reliable method of controlling fertility in plants would offer the opportunity for improved plant breeding. This is especially true for development of maize hybrids, which relies upon some sort of male sterility system and where a female sterility system would reduce production costs.
The development of maize hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection are two of the breeding methods used to develop inbred lines from populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which new inbred lines are developed by selfing and selection of desired phenotypes. A hybrid maize variety is the cross of two such inbred lines, each of which may have one or more desirable characteristics lacked by the other or which complement the other. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential. The hybrid progeny of the first generation is designated F1. In the development of hybrids only the F1 hybrid plants are sought. The F1 hybrid is more vigorous than its inbred parents. This hybrid vigor, or heterosis, can be manifested in many ways, including increased vegetative growth and increased yield.
Hybrid maize seed can be produced by a male sterility system incorporating manual detasseling. To produce hybrid seed, the male tassel is removed from the growing female inbred parent, which can be planted in various alternating row patterns with the male inbred parent. Consequently, providing that there is sufficient isolation from sources of foreign maize pollen, the ears of the female inbred will be fertilized only with pollen from the male inbred. The resulting seed is therefore hybrid (F1) and will form hybrid plants.
Environmental variation in plant development can result in plants tasseling after manual detasseling of the female parent is completed. Or, a detasseler might not completely remove the tassel of a female inbred plant. In any event, the result is that the female plant will successfully shed pollen and some female plants will be self-pollinated. This will result in seed of the female inbred being harvested along with the hybrid seed which is normally produced. Female inbred seed is not as productive as F1 seed. In addition, the presence of female inbred seed can represent a germplasm security risk for the company producing the hybrid.
Alternatively, the female inbred can be mechanically detasseled by machine. Mechanical detasseling is approximately as reliable as hand detasseling, but is faster and less costly. However, most detasseling machines produce more damage to the plants than hand detasseling. Thus, no form of detasseling is presently entirely satisfactory, and a need continues to exist for alternatives which further reduce production costs and to eliminate self-pollination of the female parent in the production of hybrid seed.
A reliable system of genetic male sterility would provide advantages. The laborious detasseling process can be avoided in some genotypes by using cytoplasmic male-sterile (CMS) inbreds. In the absence of a fertility restorer gene, plants of a CMS inbred are male sterile as a result of factors resulting from the cytoplasmic, as opposed to the nuclear, genome. Thus, this characteristic is inherited exclusively through the female parent in maize plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile. Usually seed from detasseled normal maize and CMS produced seed of the same hybrid must be blended to insure that adequate pollen loads are available for fertilization when the hybrid plants are grown and to insure cytoplasmic diversity.
There can be other drawbacks to CMS. One is an historically observed association of a specific variant of CMS with susceptibility to certain crop diseases. This problem has discouraged widespread use of that CMS variant in producing hybrid maize and has had a negative impact on the use of CMS in maize in general.
One type of genetic sterility is disclosed in U.S. Pat. Nos. 4,654,465 and 4,727,219 to Brar, et al. However, this form of genetic male sterility requires maintenance of multiple mutant genes at separate locations within the genome and requires a complex marker system to track the genes and make use of the system convenient. Patterson also described a genic system of chromosomal translocations which can be effective, but which are complicated. (See, U.S. Pat. Nos. 3,861,709 and 3,710,511.)
Many other attempts have been made to improve on these drawbacks. For example, Fabijanski, et al., developed several methods of causing male sterility in plants (see EPO 89/3010153.8 publication no. 329,308 and PCT application PCT/CA90/00037 published as WO 90/08828). One method includes delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter. Another involves an antisense system in which a gene critical to fertility is identified and an antisense to the gene inserted in the plant. Mariani, et al. also shows several cytotoxic antisense systems. See EP 89/401, 194. Still other systems use “repressor” genes which inhibit the expression of another gene critical to male sterility. PCT/GB90/00102, published as WO 90/08829.
A still further improvement of this system is one described at U.S. Pat. No. 5,478,369 (incorporated herein by reference) in which a method of imparting controllable male sterility is achieved by silencing a gene native to the plant that is critical for male fertility and replacing the native DNA with the gene critical to male fertility linked to an inducible promoter controlling expression of the gene. The plant is thus constitutively sterile, becoming fertile only when the promoter is induced and its attached male fertility gene is expressed.
As noted, an essential aspect of much of the work underway with male sterility systems is the identification of genes impacting male fertility.
Such a gene can be used in a variety of systems to control male fertility including those described herein. Previously, a male fertility gene has been identified in Arabidopsis thaliana and used to produce a male sterile plant. Aarts, et al., “Transposon Tagging of a Male Sterility Gene in Arabidopsis”, Nature, 363:715-717 (Jun. 24, 1993). U.S. Pat. No. 5,478,369 discloses therein one such gene impacting male fertility. In the present invention the inventors provide novel DNA molecules and the amino acid sequence encoded that are critical to male fertility in plants. These can be used in any of the systems where control of fertility is useful, including those described above.
Thus, one object of the invention is to provide a nucleic acid sequence, the expression of which is critical to male fertility in plants.
Another object of the invention is to provide a DNA molecule encoding an amino acid sequence, the expression of which is critical to male fertility in plants.
Yet another object of the invention is to provide a promoter of such nucleotide sequence and its essential sequences.
A further object of the invention is to provide a method of using such DNA molecules to mediate male fertility in plants.
Further objects of the invention will become apparent in the description and claims that follow.
SUMMARY OF THE INVENTION
This invention relates to nucleic acid sequences, and, specifically, DNA molecules and the amino acid encoded by the DNA molecules, which are critical to male fertility. A promoter of the DNA is identified, as well as its essential sequences. It also relates to use of such DNA molecules to mediate fertility in plants.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a locus map of the male fertility gene Ms26.
FIG. 2A is a Southern blot of the ms26-m2::Mu8 family hybridized with a Mu8 probe;
FIG. 2B is a Southern blot of the ms26-m2::Mu8 family hybridized with a PstI fragment isolated from the ms26 clone.
FIG. 3. is a Northern Blot analysis gel hybridized with a PstI fragment isolated from the Ms26 gene.
FIG. 4A-4D is the sequence of Ms26 (The cDNA is SEQ ID NO: 1, the protein is SEQ ID NOS: 2 and 34)
FIG. 5A-D is a comparison of the genomic Ms26 sequence (Residues 1051-3326 of SEQ ID NO: 7) with the cDNA of Ms26 (SEQ ID NO: 1).
FIG. 6A is a Northern analysis gel showing expression in various plant tissues and FIG. 6B is a gel showing expression stages of microsporogenesis
FIG. 7 is the full length promoter of Ms26 (SEQ ID NO: 5)
FIG. 8 is a bar graph showing luciferase activity after deletions of select regions of the Ms26 promoter.
FIG. 9 shows essential regions of the Ms26 promoter (SEQ ID NO: 6).
FIG. 10 is a bar graph showing luciferase activity after substitution by restriction site linker scanning of select small (9-10 bp) regions of the Ms26 essential promoter fragment.
FIG. 11A and 11B is a comparison of the nucleotide sequence (SEQ ID NO: 3) from the Ms26 orthologue from a sorghum panicle and Ms26 maize cDNA (Residues 201-750 of SEQ ID NO: 1), and the sorghum protein sequence (SEQ ID NO: 4) and Ms26 maize protein (Residues 87-244 of SEQ ID NO; 2).
FIG. 12 is a representation of the mapping of the male sterility gene ms26.
FIG. 13 shows a sequence comparison of the region of excision of the ms26-ref allele (SEQ ID NO: 8) with wild-type Ms26 (SEQ ID NO: 9).
FIG. 14A shows a translated protein sequence alignment between regions of the CYP704B1, a P450 gene (SEQ ID NO: 12) and Ms26 (SEQ ID NO: 13); FIG. 14B shows the phylogenetic tree analysis of select P450 genes.
FIG. 15 demonstrates the heme binding domain frame shift, showing the translated sequence alignment of regions of the Ms26 cDNA (SEQ ID NOS: 14 and 28-29), the genomic regions of exon 5 in fertile plants (SEQ ID NOS: 15 and 30-31) and sterile plants (SEQ ID NOS: 16 and 32-33).
FIG. 16 shows alignment of the Ms26 promoter of corn (Residues 650-1089 of SEQ ID NO: 5), sorghum (SEQ ID NO: 19) and rice (SEQ ID NO: 20).
FIG. 17 shows alignment of the maize Ms26 protein (SEQ ID NO: 21); rice Ms26 protein (SEQ ID NO: 18) and sorghum Ms26 protein (SEQ ID NO: 22) along with a consensus sequence (SEQ ID NO: 35).



DISCLOSURE OF THE INVENTION
All references referred to are incorporated herein by reference.
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 therein are standard methodologies well known to one of ordinary skill in the art. The materials, methods and examples are illustrative only and not limiting.
Genetic male sterility results from a mutation, suppression, or other impact to one of the genes critical to a specific step in microsporogenesis, the term applied to the entire process of pollen formulation. These genes can be collectively referred to as male fertility genes (or, alternatively, male sterility genes). There are many steps in the overall pathway where gene function impacts fertility. This seems aptly supported by the frequency of genetic male sterility in maize. New alleles of male sterility mutants are uncovered in materials that range from elite inbreds to unadapted populations. To date, published genetic male sterility research has been mostly descriptive. Some efforts have been made to establish the mechanism of sterility in maize, but few have been satisfactory. This should not be surprising given the number of genes that have been identified as being responsible for male sterility. One mechanism is unlikely to apply to all mutations.
At U.S. Pat. No. 5,478,369 there is described a method by which a male sterility gene was tagged and cloned on maize chromosome 9. Previously, there has been described a male sterility gene on chromosome 9, ms2, which has never been cloned and sequenced. It is not allelic to the gene referred to in the '369 patent. See Albertsen, M. and Phillips, R. L., “Developmental Cytology of 13 Genetic Male Sterile Loci in Maize” Canadian Journal of Genetics & Cytology 23:195-208 (January 1981). The only fertility gene cloned before that had been the Arabadopsis gene described at Aarts, et al., supra.
Thus the invention includes using the sequences shown herein it impacts male fertility in a plant, that is, to control male fertility by manipulation of the genome using the genes of the invention. By way of example, without limitation, any of the methods described supra can be used with the sequence of the invention such as introducing a mutant sequence into a plant to cause sterility, causing mutation to the native sequence, introducing an antisense of the sequence into the plant, linking it with other sequences to control its expression, or any one of a myriad of processes available to one skilled in the art to impact male fertility in a plant.
The Ms26 gene described herein is located on maize chromosome 1 and its dominant allele is critical to male fertility. The locus map is represented at FIG. 1. It can be used in the systems described above, and other systems impacting male fertility.
The maize family cosegregating for sterility was named ms*-SBMu200 and was found to have an approximately 5.5 Kb EcoRI fragment that hybridized with a Mu8 probe (2A). A genomic clone from the family was isolated which contained a Mu8 transposon. A probe made from DNA bordering the transposon was found to hybridize to the same  ̃5.5 Kb EcoR1 fragment (2B). This probe was used to isolate cDNA clones from a tassel cDNA library. The cDNA is 1906 bp, and the Mu insertion occurred in exon 1 of the gene. This probe was also used to map the mutation in an RFLP mapping population. The mutant mapped to the short arm of chromosome 1, near Ms26. Allelism crosses between ms26-ref and ms*-SBMu200 showed that these were allelic, indicating that the mutations occurred in the same gene. The ms*-SBMu200 allele was renamed ms26-m2::Mu8. Two additional alleles for the Ms26 gene were cloned, one containing a Mutator element in the second exon, named ms26-m3::Mu*, and one containing an unknown transposon in the fifth exon from the ms26-ref allele. SEQ ID NO: 7 (discussed further below) represents the genomic nucleotide sequence. Expression patterns, as determined by Northern analysis, show tassel specificity with peak expression at about the quartet to quartet release stages of microsporogenesis.
Further, it will be evident to one skilled in the art that variations, mutations, derivations including fragments smaller than the entire sequence set forth may be used which retain the male sterility controlling properties of the gene. One of ordinary skill in the art can readily assess the variant or fragment by introduction into plants homozygous for a stable male sterile allele of Ms26, followed by observation of the plant's male tissue development.
The sequences of the invention may be isolated from any plant, including, but not limited to corn (Zea mays), canola (Brassica napus, Brassica rapa ssp.), alfalfa (Medicago sativa), rice (Oryza sativa), rye (Secale cereale), sorghum (Sorghum bicolor, Sorghum vulgare), sunflower (Helianthus annuus), wheat (Triticum aestivum), soybean (Glycine max), tobacco (Nicotiana tabacum), millet (Panicum spp.), potato (Solanum tuberosum), peanuts (Arachis hypogaea), cotton (Gossypium hirsutum), sweet potato (Ipomoea batatus), cassaya (Manihot esculenta), coffee (Cofea spp.), coconut (Cocos nucifera), pineapple (Ananas comosus), citrus trees (Citrus spp.), cocoa (Theobroma cacao), tea (Camellia sinensis), banana (Musa spp.), avocado (Persea americana), fig (Ficus casica), guava (Psidium guajava), mango (Mangifera indica), olive (Olea europaea), oats (Avena sativa), barley (Hordeum vulgare), vegetables, ornamentals, and conifers. Preferably, plants include corn, soybean, sunflower, safflower, canola, wheat, barley, rye, alfalfa, rice, cotton and sorghum.
Sequences from other plants may be isolated according to well-known techniques based on their sequence homology to the homologous coding region of the coding sequences set forth herein. In these techniques, all or part of the known coding sequence is used as a probe which selectively hybridizes to other sequences present in a population of cloned genomic DNA fragments (i.e. genomic libraries) from a chosen organism. Methods are readily available in the art for the hybridization of nucleic acid sequences. 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, N.Y. (1993); and Current Protocols in Molecular Biology, Chapter 2, Ausubel, et al., Eds., Greene Publishing and Wiley-Interscience, New York (1995).
Thus the invention also includes those nucleotide sequences which selectively hybridize to the Ms26 nucleotide sequences under stringent conditions. In referring to a sequence that “selectively hybridizes” with Ms26, the term includes reference to hybridization, under stringent hybridization conditions, of a nucleic acid sequence to the 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.
The terms “stringent conditions” or “stringent hybridization conditions” includes reference to conditions under which a probe will hybridize to its target sequence, to a detectably greater degree than to other sequences (e.g., at least 2-fold over background). Stringent conditions are target-sequence-dependent and will differ depending on the structure of the polynucleotide. By controlling the stringency of the hybridization and/or washing conditions, target sequences can be identified which are 100% complementary to a 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). Generally, probes of this type are in a range of about 1000 nucleotides in length to about 250 nucleotides in length.
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, N.Y. (1993); and Current Protocols in Molecular Biology, Chapter 2, Ausubel, et al., Eds., Greene Publishing and Wiley-Interscience, New York (1995). See also Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.).
In general, sequences that correspond to the nucleotide sequences of the present invention and hybridize to the nucleotide sequence disclosed herein will be at least 50% homologous, 70% homologous, and even 85% homologous or more with the disclosed sequence. That is, the sequence similarity between probe and target may range, sharing at least about 50%, about 70%, and even about 85% sequence similarity.
Specificity is typically the function of post-hybridization washes, the critical factors being the ionic strength and temperature of the final wash solution. Generally, stringent wash temperature conditions are selected to be about 5° C. to about 2° C. lower than the melting point (Tm) for the specific sequence at a defined ionic strength and pH. The melting point, or denaturation, of DNA occurs over a narrow temperature range and represents the disruption of the double helix into its complementary single strands. The process is described by the temperature of the midpoint of transition, Tm, which is also called the melting temperature. Formulas are available in the art for the determination of melting temperatures.
Preferred hybridization conditions for the nucleotide sequence of the invention include hybridization at 42° C. in 50% (w/v) formamide, 6×SSC, 0.5% (w/v) SDS, 100 (g/ml salmon sperm DNA. Exemplary low stringency washing conditions include hybridization at 42° C. in a solution of 2×SSC, 0.5% (w/v) SDS for 30 minutes and repeating. Exemplary moderate stringency conditions include a wash in 2×SSC, 0.5% (w/v) SDS at 50° C. for 30 minutes and repeating. Exemplary high stringency conditions include a wash in 0.1×SSC, 0.1% (w/v) SDS, at 65° C. for 30 minutes to one hour and repeating. Sequences that correspond to the promoter of the present invention may be obtained using all the above conditions. For purposes of defining the invention, the high stringency conditions are used.
The following terms are used to describe the sequence relationships between two or more nucleic acids or polynucleotides: (a) “reference sequence”, (b) “comparison window”, (c) “sequence identity”, and (d) “percentage of sequence identity.”
(a) 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.
(b) As used herein, “comparison window” makes reference to a contiguous and specified segment of a polynucleotide sequence, wherein 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, or 100 nucleotides in length, 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 aligning sequences for comparison are well-known in the art. Thus, the determination of percent sequence identity between any two sequences can be accomplished using a mathematical algorithm. Non-limiting examples of such mathematical algorithms are the algorithm of Myers and Miller (1988) CABIOS 4: 11-17; the local alignment algorithm of Smith et al. (1981) Adv. Appl. Math. 2: 482; the global alignment algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48: 443-453; the search-for-local-alignment-method of Pearson and Lipman (1988) Proc. Natl. Acad. Sci. 85: 2444-2448; the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87: 2264, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90: 5873-5877.
Computer implementations of these mathematical algorithms can be utilized for comparison of sequences to determine sequence identity. Such implementations include, but are not limited to: CLUSTAL in the PC/Gene program (available from Intelligenetics, Mountain View, Calif.); the ALIGN program (Version 2.0) and GAP, BESTFIT, BLAST, FASTA, and TFASTA in the GCG Wisconsin Genetics Software Package, Version 10 (available from Accelrys Inc., 9685 Scranton Road, San Diego, Calif., USA). Alignments using these programs can be performed using the default parameters. The CLUSTAL program is well described by Higgins et al. (1988) Gene 73: 237-244 (1988); Higgins et al. (1989) CABIOS 5: 151-153; Corpet et al. (1988) Nucleic Acids Res. 16: 10881-90; Huang et al. (1992) CABIOS 8: 155-65; and Pearson et al. (1994) Meth. Mol. Biol. 24: 307-331. The ALIGN program is based on the algorithm of Myers and Miller (1988) supra. A PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used with the ALIGN program when comparing amino acid sequences. The BLAST programs of Altschul et al (1990) J. Mol. Biol. 215: 403 are based on the algorithm of Karlin and Altschul (1990) supra. BLAST nucleotide searches can be performed with the BLASTN program, score=100, wordlength=12, to obtain nucleotide sequences homologous to a nucleotide sequence encoding a protein of the invention. BLAST protein searches can be performed with the BLASTX program, score=50, wordlength=3, to obtain amino acid sequences homologous to a protein or polypeptide of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST (in BLAST 2.0) can be utilized as described in Altschul et al. (1997) Nucleic Acids Res. 25: 3389. Alternatively, PSI-BLAST (in BLAST 2.0) can be used to perform an iterated search that detects distant relationships between molecules. See Altschul et al. (1997) supra. When utilizing BLAST, Gapped BLAST, PSI-BLAST, the default parameters of the respective programs (e.g., BLASTN for nucleotide sequences, BLASTX for proteins) can be used. See http://www.ncbi.nlm.nih.gov. Alignment may also be performed manually by inspection.
Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using GAP Version 10 using the following parameters: % identity and % similarity for a nucleotide sequence using GAP Weight of 50 and Length Weight of 3 and the nwsgapdna.cmp scoring matrix; % identity and % similarity for an amino acid sequence using GAP Weight of 8 and Length Weight of 2; and the BLOSUM62 scoring matrix or any equivalent program thereof. By “equivalent program” is intended any sequence comparison program that, for any two sequences in question, generates an alignment having identical nucleotide or amino acid residue matches and an identical percent sequence identity when compared to the corresponding alignment generated by GAP Version 10.
GAP uses the algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48: 443-453, 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 GCG Wisconsin Genetics Software Package for protein sequences are 8 and 2, respectively. For nucleotide sequences the default gap creation penalty is 50 while the default gap extension penalty is 3. The gap creation and gap extension penalties can be expressed as an integer selected from the group of integers consisting of from 0 to 200. 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, 25, 30, 35, 40, 45, 50, 55, 60, 65 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 GCG Wisconsin Genetics Software Package is BLOSUM62 (see Henikoff and Henikoff (1989) Proc. Natl. Acad. Sci. USA 89:10915).
(c) As used herein, “sequence identity” or “identity” in the context of two nucleic acid or polypeptide sequences makes reference 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.).
(d) 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 use of the term “polynucleotide” is not intended to limit the present invention to polynucleotides comprising DNA. Those of ordinary skill in the art will recognize that polynucleotides can comprise ribonucleotides and combinations of ribonucleotides and deoxyribonucleotides. Such deoxyribonucleotides and ribonucleotides include both naturally occurring molecules and synthetic analogues. The polynucleotides of the invention also encompass all forms of sequences including, but not limited to, single-stranded forms, double-stranded forms, hairpins, stem-and-loop structures, and the like.
Identity to the sequence of the present invention would mean a polynucleotide sequence having at least 65% sequence identity, more preferably at least 70% sequence identity, more preferably at least 75% sequence identity, more preferably at least 80% identity, more preferably at least 85% sequence identity, more preferably at least 90% sequence identity and most preferably at least 95% sequence identity.
Promoter regions can be readily identified by one skilled in the art. The putative start codon containing the ATG motif is identified and upstream from the start codon is the presumptive promoter. By “promoter” is intended a regulatory region of DNA usually comprising a TATA box capable of directing RNA polymerase II to initiate RNA synthesis at the appropriate transcription initiation site for a particular coding sequence. A promoter can additionally comprise other recognition sequences generally positioned upstream or 5′ to the TATA box, referred to as upstream promoter elements, which influence the transcription initiation rate. It is recognized that having identified the nucleotide sequences for the promoter region disclosed herein, it is within the state of the art to isolate and identify further regulatory elements in the region upstream of the TATA box from the particular promoter region identified herein. Thus the promoter region disclosed herein is generally further defined by comprising upstream regulatory elements such as those responsible for tissue and temporal expression of the coding sequence, enhancers and the like. In the same manner, the promoter elements which enable expression in the desired tissue such as male tissue can be identified, isolated, and used with other core promoters to confirm male tissue-preferred expression. By core promoter is meant the minimal sequence required to initiate transcription, such as the sequence called the TATA box which is common to promoters in genes encoding proteins. Thus the upstream promoter of Ms26 can optionally be used in conjunction with its own or core promoters from other sources. the promoter may be native or non-native to the cell in which it is found.
The isolated promoter sequence of the present invention can be modified to provide for a range of expression levels of the heterologous nucleotide sequence. Less than the entire promoter region can be utilized and the ability to drive anther-preferred expression retained. However, it is recognized that expression levels of mRNA can be decreased with deletions of portions of the promoter sequence. Thus, the promoter can be modified to be a weak or strong promoter. Generally, by “weak promoter” is intended a promoter that drives expression of a coding sequence at a low level. By “low level” is intended 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 at about 1/10 transcripts to about 1/100 transcripts to about 1/1,000 transcripts. Generally, at least about 30 nucleotides of an isolated promoter sequence will be used to drive expression of a nucleotide sequence. It is recognized that to increase transcription levels, enhancers can be utilized in combination with the promoter regions of the invention. Enhancers are nucleotide sequences that act to increase the expression of a promoter region. Enhancers are known in the art and include the SV40 enhancer region, the 35S enhancer element, and the like.
The promoter of the present invention can be isolated from the 5′ region of its native coding region of 5′ untranslation region (5′UTR). Likewise the terminator can be isolated from the 3′ region flanking its respective stop codon. The term “isolated” refers to material such as a nucleic acid or protein which is substantially or essentially free from components which normally accompany or interact with the material as found in it naturally occurring environment or if the material is in its natural environment, the material has been altered by deliberate human intervention to a composition and/or placed at a locus in a cell other than the locus native to the material. Methods for isolation of promoter regions are well known in the art.
“Functional variants” of the regulatory sequences are also encompassed by the compositions of the present invention. Functional variants include, for example, the native regulatory sequences of the invention having one or more nucleotide substitutions, deletions or insertions. Functional variants of the invention may be created by site-directed mutagenesis, induced mutation, or may occur as allelic variants (polymorphisms).
As used herein, a “functional fragment” is a regulatory sequence variant formed by one or more deletions from a larger regulatory element. For example, the 5′ portion of a promoter up to the TATA box near the transcription start site can be deleted without abolishing promoter activity, as described by Opsahl-Sorteberg, H-G. et al., “Identification of a 49-bp fragment of the HvLTP2 promoter directing aleruone cell specific expression” Gene 341:49-58 (2004). Such variants should retain promoter activity, particularly the ability to drive expression in male tissues. Activity can be measured by Northern blot analysis, reporter activity measurements when using transcriptional fusions, and the like. See, for example, Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2nd ed. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.), herein incorporated by reference.
Functional fragments can be obtained by use of restriction enzymes to cleave the naturally occurring regulatory element nucleotide sequences disclosed herein; by synthesizing a nucleotide sequence from the naturally occurring DNA sequence; or can be obtained through the use of PCR technology See particularly, Mullis et al. (1987) Methods Enzymol. 155:335-350, and Erlich, ed. (1989) PCR Technology (Stockton Press, New York).
Sequences which hybridize to the regulatory sequences of the present invention are within the scope of the invention. Sequences that correspond to the promoter sequences of the present invention and hybridize to the promoter sequences disclosed herein will be at least 50% homologous, 70% homologous, and even 85% homologous or more with the disclosed sequence.
Smaller fragments may yet contain the regulatory properties of the promoter so identified and deletion analysis is one method of identifying essential regions. Deletion analysis can occur from both the 5′ and 3′ ends of the regulatory region. Fragments can be obtained by site-directed mutagenesis, mutagenesis using the polymerase chain reaction and the like. (See, Directed Mutagenesis: A Practical Approach IRL Press (1991)). The 3′ deletions can delineate the essential region and identify the 3′ end so that this region may then be operably linked to a core promoter of choice. Once the essential region is identified, transcription of an exogenous gene may be controlled by the essential region plus a core promoter. By core promoter is meant the sequence called the TATA box which is common to promoters in all genes encoding proteins. Thus the upstream promoter of Ms26 can optionally be used in conjunction with its own or core promoters from other sources. The promoter may be native or non-native to the cell in which it is found.
The core promoter can be any one of known core promoters such as the Cauliflower Mosaic Virus 35S or 19S promoter (U.S. Pat. No. 5,352,605), ubiquitin promoter (U.S. Pat. No. 5,510,474) the IN2 core promoter (U.S. Pat. No. 5,364,780) or a Figwort Mosaic Virus promoter (Gruber, et al. “Vectors for Plant Transformation” Methods in Plant Molecular Biology and Biotechnology) et al. eds, CRC Press pp. 89-119 (1993)).
The regulatory region of Ms26 has been identified as including the 1005 bp region upstream of the putative TATA box. See FIG. 7. Further, using the procedures outlined above, it has been determined that an essential region of the promoter includes the −180 bp upstream of the TATA box and specifically, the −176 to −44 region is particularly essential.
Promoter sequences from other plants may be isolated according to well-known techniques based on their sequence homology to the promoter sequence set forth herein. In these techniques, all or part of the known promoter sequence is used as a probe which selectively hybridizes to other sequences present in a population of cloned genomic DNA fragments (i.e. genomic libraries) from a chosen organism. Methods are readily available in the art for the hybridization of nucleic acid sequences.
The entire promoter sequence or portions thereof can be used as a probe capable of specifically hybridizing to corresponding promoter sequences. To achieve specific hybridization under a variety of conditions, such probes include sequences that are unique and are preferably at least about 10 nucleotides in length, and most preferably at least about nucleotides in length. Such probes can be used to amplify corresponding promoter sequences from a chosen organism by the well-known process of polymerase chain reaction (PCR). This technique can be used to isolate additional promoter sequences from a desired organism or as a diagnostic assay to determine the presence of the promoter sequence in an organism. Examples include hybridization screening of plated DNA libraries (either plaques or colonies; see e.g. Innis et al., eds., (1990) PCR Protocols, A Guide to Methods and Applications, Academic Press).
Further, a promoter of the present invention can be linked with nucleotide sequences other than the Ms26 gene to express other heterologous nucleotide sequences. The nucleotide sequence for the promoter of the invention, as well as fragments and variants thereof, can be provided in expression cassettes along with heterologous nucleotide sequences for expression in the plant of interest, more particularly in the male tissue of the plant. Such an expression cassette is provided with a plurality of restriction sites for insertion of the nucleotide sequence to be under the transcriptional regulation of the promoter. These expression cassettes are useful in the genetic manipulation of any plant to achieve a desired phenotypic response. Examples of other nucleotide sequences which can be used as the exogenous gene of the expression vector with the Ms26 promoter include complementary nucleotidic units such as antisense molecules (callase antisense RNA, bamase antisense RNA and chalcone synthase antisense RNA, Ms45 antisense RNA), ribozymes and external guide sequences, an aptamer or single stranded nucleotides. The exogenous nucleotide sequence can also encode auxins, rol B, cytotoxins, diptheria toxin, DAM methylase, avidin, or may be selected from a prokaryotic regulatory system. By way of example, Mariani, et al., Nature; Vol. 347; pp. 737; (1990), have shown that expression in the tapetum of either Aspergillus oryzae RNase-T1 or an RNase of Bacillus amyloliquefaciens, designated “barnase,” induced destruction of the tapetal cells, resulting in male infertility. Quaas, et al., Eur. J. Biochem. Vol. 173: pp. 617 (1988), describe the chemical synthesis of the RNase-T1, while the nucleotide sequence of the barnase gene is disclosed in Hartley, J. Molec. Biol.; Vol. 202: pp. 913 (1988). The rolB gene of Agrobacterium rhizogenes codes for an enzyme that interferes with auxin metabolism by catalyzing the release of free indoles from indoxyl-β-glucosides. Estruch, et al., EMBO J. Vol. 11: pp. 3125 (1991) and Spena, et al., Theor. Appl. Genet.; Vol. 84: pp. 520 (1992), have shown that the anther-specific expression of the rolB gene in tobacco resulted in plants having shriveled anthers in which pollen production was severely decreased and the rolB gene is an example of a gene that is useful for the control of pollen production. Slightom, et al., J. Biol. Chem. Vol. 261: pp. 108 (1985), disclose the nucleotide sequence of the rolB gene. DNA molecules encoding the diphtheria toxin gene can be obtained from the American Type Culture Collection (Rockville, Md.), ATCC No. 39359 or ATCC No. 67011 and see Fabijanski, et al., E.P. Appl. No. 90902754.2, “Molecular Methods of Hybrid Seed Production” for examples and methods of use. The DAM methylase gene is used to cause sterility in the methods discussed at U.S. Pat. No. 5,689,049 and PCT/US95/15229 Cigan, A. M. and Albertsen, M. C., “Reversible Nuclear Genetic System for Male Sterility in Transgenic Plants”. Also see discussion of use of the avidin gene to cause sterility at U.S. Pat. No. 5,962,769 “Induction of Male Sterility in Plants by Expression of High Levels of Avidin” by Albertsen et al.
The invention includes vectors with the Ms26 gene. A vector is prepared comprising Ms26, a promoter that will drive expression of the gene in the plant and a terminator region. As noted, the promoter in the construct may be the native promoter or a substituted promoter which will provide expression in the plant. Selection of the promoter will depend upon the use intended of the gene. The promoter in the construct may be an inducible promoter, so that expression of the sense or antisense molecule in the construct can be controlled by exposure to the inducer.
Other components of the vector may be included, also depending upon intended use of the gene. Examples include selectable markers, targeting or regulatory sequences, stabilizing or leader sequences, etc. General descriptions and examples of plant expression vectors and reporter genes can be found in Gruber, et al., “Vectors for Plant Transformation” in Method in Plant Molecular Biology and Biotechnology, Glick et al eds; CRC Press pp. 89-119 (1993). The selection of an appropriate expression vector will depend upon the host and the method of introducing the expression vector into the host. The expression cassette will also include at the 3′ terminus of the heterologous nucleotide sequence of interest, a transcriptional and translational termination region functional in plants. The termination region can be native with the promoter nucleotide sequence of the present invention, can be native with the DNA sequence of interest, or can be derived from another source. Convenient termination regions are available from the Ti-plasmid of A. tumefaciens, such as the octopine synthase and nopaline synthase termination regions. See also, Guerineau et al. Mol. Gen. Genet. 262:141-144 (1991); Proudfoot, Cell 64:671-674 (1991); Sanfacon et al. Genes Dev. 5:141-149 (1991); Mogen et al. Plant Cell 2:1261-1272 (1990); Munroe et al. Gene 91:151-158 (1990); Ballas et al. Nucleic Acids Res. 17:7891-7903 (1989); Joshi et al. Nucleic Acid Res. 15:9627-9639 (1987).
The expression cassettes can additionally contain 5′ leader sequences. Such leader sequences can act to enhance translation. Translation leaders are known in the art and include: picornavirus leaders, for example, EMCV leader (Encephalomyocarditis 5′ noncoding region), Elroy-Stein et al. Proc. Nat. Acad. Sci. USA 86:6126-6130 (1989); potyvirus leaders, for example, TEV leader (Tobacco Etch Virus), Allison et al.; MDMV leader (Maize Dwarf Mosaic Virus), Virology 154:9-20 (1986); human immunoglobulin heavy-chain binding protein (BiP), Macejak et al. Nature 353:90-94 (1991); untranslated leader from the coat protein mRNA of alfalfa mosaic virus (AMV RNA 4), Jobling et al. Nature 325:622-625 (1987); Tobacco mosaic virus leader (TMV), Gallie et al. (1989) Molecular Biology of RNA, pages 237-256; and maize chlorotic mottle virus leader (MCMV) Lommel et al. Virology 81:382-385 (1991). See also Della-Cioppa et al. Plant Physiology 84:965-968 (1987). The cassette can also contain sequences that enhance translation and/or mRNA stability such as introns.
In those instances where it is desirable to have the expressed product of the heterologous nucleotide sequence directed to a particular organelle, particularly the plastid, amyloplast, or to the endoplasmic reticulum, or secreted at the cell's surface or extracellularly, the expression cassette can further comprise a coding sequence for a transit peptide. Such transit peptides are well known in the art and include, but are not limited to, the transit peptide for the acyl carrier protein, the small subunit of RUBISCO, plant EPSP synthase, and the like. One skilled in the art will readily appreciate the many options available in expressing a product to a particular organelle. For example, the barley alpha amylase sequence is often used to direct expression to the endoplasmic reticulum (Rogers, J. Biol. Chem. 260:3731-3738 (1985)). Use of transit peptides is well known (e.g., see U.S. Pat. Nos. 5,717,084; 5,728,925).
In preparing the expression cassette, the various DNA fragments can be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers can be employed to join the DNA fragments or other manipulations can be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, or the like. For this purpose, in vitro mutagenesis, primer repair, restriction digests, annealing, and resubstitutions, such as transitions and transversions, can be involved.
As noted herein, the present invention provides vectors capable of expressing genes of interest under the control of the promoter. In general, the vectors should be functional in plant cells. At times, it may be preferable to have vectors that are functional in E. coli (e.g., production of protein for raising antibodies, DNA sequence analysis, construction of inserts, obtaining quantities of nucleic acids). Vectors and procedures for cloning and expression in E. coli are discussed in Sambrook et al. (supra).
The transformation vector comprising the promoter sequence of the present invention operably linked to a heterologous nucleotide sequence in an expression cassette, can also contain at least one additional nucleotide sequence for a gene to be cotransformed into the organism. Alternatively, the additional sequence(s) can be provided on another transformation vector.
Reporter genes can be included in the transformation vectors. Examples of suitable reporter genes known in the art can be found in, for example, Jefferson et al. (1991) in Plant Molecular Biology Manual, ed. Gelvin et al. (Kluwer Academic Publishers), pp. 1-33; DeWet et al. Mol. Cell. Biol. 7:725-737 (1987); Goff et al. EMBO J. 9:2517-2522 (1990); Kain et al. BioTechniques 19:650-655 (1995); and Chiu et al. Current Biology 6:325-330 (1996).
Selectable marker genes for selection of transformed cells or tissues can be included in the transformation vectors. These can include genes that confer antibiotic resistance or resistance to herbicides. Examples of suitable selectable marker genes include, but are not limited to, genes encoding resistance to chloramphenicol, Herrera Estrella et al. EMBO J. 2:987-992 (1983); methotrexate, Herrera Estrella et al. Nature 303:209-213 (1983); Meijer et al. Plant Mol. Biol. 16:807-820 (1991); hygromycin, Waldron et al. Plant Mol. Biol. 5:103-108 (1985); Zhijian et al. Plant Science 108:219-227 (1995); streptomycin, Jones et al. Mol. Gen. Genet. 210:86-91 (1987); spectinomycin, Bretagne-Sagnard et al. Transgenic Res. 5:131-137 (1996); bleomycin, Hille et al. Plant Mol. Biol. 7:171-176 (1990); sulfonamide, Guerineau et al. Plant Mol. Biol. 15:127-136 (1990); bromoxynil, Stalker et al. Science 242:419-423 (1988); glyphosate, Shaw et al. Science 233:478-481 (1986); phosphinothricin, DeBlock et al. EMBO J. 6:2513-2518 (1987).
The method of transformation/transfection is not critical to the instant invention; various methods of transformation or transfection are currently available. As newer methods are available to transform crops or other host cells they may be directly applied. Accordingly, a wide variety of methods have been developed to insert a DNA sequence into the genome of a host cell to obtain the transcription or transcript and translation of the sequence to effect phenotypic changes in the organism. Thus, any method which provides for efficient transformation/transfection may be employed.
Methods for introducing expression vectors into plant tissue available to one skilled in the art are varied and will depend on the plant selected. Procedures for transforming a wide variety of plant species are well known and described throughout the literature. See, for example, Miki et al, “Procedures for Introducing Foreign DNA into Plants” in Methods in Plant Molecular Biotechnology, supra; Klein et al, Bio/Technology 10:268 (1992); and Weising et al., Ann. Rev. Genet. 22: 421-477 (1988). For example, the DNA construct may be introduced into the genomic DNA of the plant cell using techniques such as microprojectile-mediated delivery, Klein et al., Nature 327: 70-73 (1987); electroporation, Fromm et al., Proc. Natl. Acad. Sci. 82: 5824 (1985); polyethylene glycol (PEG) precipitation, Paszkowski et al., EMBO J. 3: 2717-2722 (1984); direct gene transfer WO 85/01856 and EP No. 0 275 069; in vitro protoplast transformation U.S. Pat. No. 4,684,611; and microinjection of plant cell protoplasts or embryogenic callus. Crossway, Mol. Gen. Genetics 202:179-185 (1985). Co-cultivation of plant tissue with Agrobacterium tumefaciens is another option, where the DNA constructs are placed into a binary vector system. See e.g., U.S. Pat. No. 5,591,616; Ishida et al., “High Efficiency Transformation of Maize (Zea mays L.) mediated by Agrobacterium tumefaciens” Nature Biotechnology 14:745-750 (1996). The virulence functions of the Agrobacterium tumefaciens host will direct the insertion of the construct into the plant cell DNA when the cell is infected by the bacteria. See, for example Horsch et al., Science 233: 496-498 (1984), and Fraley et al., Proc. Natl. Acad. Sci. 80: 4803 (1983).
Standard methods for transformation of canola are described at Moloney et al. “High Efficiency Transformation of Brassica napus using Agrobacterium Vectors” Plant Cell Reports 8:238-242 (1989). Corn transformation is described by Fromm et al, Bio/Technology 8:833 (1990) and Gordon-Kamm et al, supra. Agrobacterium is primarily used in dicots, but certain monocots such as maize can be transformed by Agrobacterium. See supra and U.S. Pat. No. 5,550,318. Rice transformation is described by Hiei et al., “Efficient Transformation of Rice (Oryza sativs L.) Mediated by Agrobacterium and Sequence Analysis of the Boundaries of the T-DNA” The Plant Journal 6(2): 271-282 (1994, Christou et al, Trends in Biotechnology 10:239 (1992) and Lee et al, Proc. Nat'l Acad. Sci. USA 88:6389 (1991). Wheat can be transformed by techniques similar to those used for transforming corn or rice. Sorghum transformation is described at Casas et al, supra and sorghum by Wan et al, Plant Physicol. 104:37 (1994). Soybean transformation is described in a number of publications, including U.S. Pat. No. 5,015,580.
Further detailed description is provided below by way of instruction and illustration and is not intended to limit the scope of the invention.
EXAMPLE 1
Identification and Cosegregation of Ms26-M2::Mu8
Families of plants from a Mutator (Mu) population were identified that segregated for plants that were mostly male sterile, with none or only a few extruded abnormal anthers, none of which had pollen present. Male sterility is expected to result from those instances where a Mu element has randomly integrated into a gene responsible for some step in microsporogenesis, disrupting its expression. Plants from a segregating F2 family in which the male sterile mutation was designated ms26*-SBMu200, were grown and classified for male fertility/sterility based on the above criteria. Leaf samples were taken and DNA subsequently isolated on approximately 20 plants per phenotypic classification, that is male fertility vs. male sterility.
Southern analysis was performed to confirm association of Mu with sterility. Southern analysis is a well known technique to those skilled in the art. This common procedure involves isolating the plant DNA, cutting with restriction endonucleases, fractioning the cut DNA by molecular weight on an agarose gel, and transferring to nylon membranes to fix the separated DNA. These membranes are subsequently hybridized with a probe fragment that was radioactively labeled with P32P-dCTP, and washed in an SDS solution. Southern, E., “Detection of Specific Sequences Among DNA Fragments by Gel Electrophoresis,” J. Mol. Biol. 98:503-317 (1975). Plants from a segregating F2 ms26*-SBMu200 family were grown and classified for male fertility/sterility. Leaf samples and subsequent DNA isolation was conducted on approximately 20 plants per phenotypic classification. DNA ( ̃7 ug) from 5 fertile and 12 sterile plants was digested with EcoRI and electrophoresed through a 0.75% agarose gel. The digested DNA was transferred to nylon membrane via Southern transfer. The membrane was hybridized with an internal fragment from the Mu8 transposon. Autoradiography of the membrane revealed cosegregation of a 5.5 Kb EcoRI fragment with the sterility phenotype as shown in FIG. 1. This EcoRI band segregated in the fertile plants suggesting a heterozygous wild type condition for the allele
EXAMPLE 2
Library Construction, Screening, and Mapping
The process of genomic library screenings is commonly known among those skilled in the art and is described at Sambrook, J., Fritsch, E. F., Maniatis T., et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor Lab Press, Plainview, N.Y. (1989). Libraries were created as follows.
DNA from a sterile plant was digested with EcoRI and run on a preparative gel. DNA with a molecular weight between 5.0 and 6.0 Kb was excised from the gel, electroeluted and ethanol precipitated. This DNA was ligated into the Lambda Zap vector (StratageneTM) using the manufacturer's protocol. The ligated DNA was packaged into phage particles using Gigapack Gold (StratageneTM). Approximately 500,000 PFU were plated and lifted onto nitrocellulose membranes. Membranes were hybridized with the Mu8 probe. A pure clone was obtained after 3 rounds of screening. The insert was excised from the phage as a plasmid and designated SBMu200-3.1. A PstI border fragment from this clone was isolated and used to reprobe the orginal EcoRI cosegregation blot as shown in FIG. 2B. The 5.5 kb EcoRI fragment is homozygous in all the sterile plants, which confirms that the correct Mu fragment was isolated. Three of the fertile plants are heterozygous for the 5.5 kb EcoRI band and a 4.3 Kb EcoRI band. Two of the fertile plants are homozygous for the 4.3 kb EcoRI band, presumably the wild type allele.
The PstI probe was used to map the ms*-SBMu200 mutation in an RFLP mapping population. The mutant mapped to the short arm of chromosome 1, near the male sterile locus, Ms26 (Loukides et al., (1995) Amer. J. Bot 82, 1017-1023). To test whether ms*-SBMu200 was an allele of ms26-ref, ms*-SBMu200 and ms26-ref were crossed with each other using a known heterozygote as the pollen donor. The testcross progeny segregated male-sterile and wild-type plants in a 1:1 ratio, indicating allelism between ms*-SBMu200 and ms26-ref. The ms*-SBMu200 allele was designated ms26-m2::Mu8. The map location is shown in FIG. 12.
EXAMPLE 3
Identification and Cloning of Additional Ms26 Alleles
Three additional Mu insertion mutations in Ms26 were identified by using a polymerase chain reaction (PCR) primer for Mu and a gene specific primer for Ms26. Sequence analyses of the PCR products showed that all three Mu insertions occurred in the second exon (FIG. 1). The F2 seeds from one of these families were grown and examined for male fertility/sterility. Southern blot analyses of this family confirmed the cosegregation of the Mu insertion in Ms26 with the male-sterile phenotype.
The ms26 allele described in Loukides et al., (1995) Amer. J. Bot 82, 1017-1023 and designated ms26-ref was also investigated. To analyze the mutation in ms26-ref, Ms26 genomic sequences were cloned from ms26-ref sterile and fertile plants. Ms26 was cloned as a  ̃4.2 kb EcoRI fragment and ms26-ref cloned as a  ̃6 kb HindIII fragment and an overlapping  ̃2.3 kb EcoRI fragment from the sterile plant. Sequence analysis revealed the presence of a new segment (1,430 bp) in the last exon of the ms26-ref allele shown in FIG. 1. An 8 bp host site duplication (GCCGGAGC) was found that flanks the inserted element and the element also contains a 15 bp terminal inverted repeat (TIR) (TAGGGGTGAAAACGG; SEQ ID NO: 23). The transposon sequence is shown in SEQ ID NO: 10. The ms26-ref genomic sequence in its entirety is shown in SEQ ID NO: 11. A variant of the ms26-ref allele was also found. Sequence analysis of this allele, designated ms26′-0406, was found to have lost the 1430 bp segment found in the last exon of the ms26-ref allele but left an 8 bp footprint at the site of insertion. Plants homozygous for the ms26′-0406 allele were male sterile. A comparison of the excision allele, ms26′-0406 (SEQ ID NO: 8) with the region in the wild-type Ms26 gene (SEQ ID NO: 9) is shown in FIG. 13.
EXAMPLE 4
Expression Analysis and cDNA Isolation
Northern analysis can be used to detect expression of genes characteristic of anther development at various states of microsporogenesis. Northern analysis is also a commonly used technique known to those skilled in the art and is similar to Southern analysis except that mRNA rather than DNA is isolated and placed on the gel. The RNA is then hybridzed with the labeled probe. Potter, E., et al., “Thyrotrotropin Releasing Hormone Exerts Rapid Nuclear Effects to Increase Production of the Primary Prolactin in RNA Transcript,” Proc. Nat. Acad. Sci. USA 78:6662-6666 (1981), Lechelt, et al., “Isolation & Molecular Analysis of the Plows,” Mol. Gen. Genet. 219:225-234 (1989). The PstI fragment from the SBMu200-3.1 clone was used to probe a Northern blot containing kernel, immature ear, seedling and tassel RNA. A signal was seen only in tassel RNA at approximately the quartet stage of microsporogenesis, as reflected in FIG. 3. The transcript is about 2.3 kb in length. The same probe was also used to screen a cDNA library constructed from mRNA isolated from meiotic to late uninucleate staged anthers. One clone, designated Ms26-8.1, was isolated from the library.
EXAMPLE 5
Sequence and Expression Analysis
The SBMu200-3.1 genomic clone and the Ms26-8.1 cDNA clone were sequenced by Loftstrand Labs Limited. Sanger, F., Nicklen, S., Coulson A. R. (1977) “DNA sequencing with chain terminating inhibitors” Proc. Natl. Acad. Sci. USA 74:5463-5467. The sequences are set forth in FIG. 4 and the comparison is at FIG. 5. The cDNA/genomic comparison reveals five introns are present in the genomic clone. The Mu8 insertion occurs in exon 1. Testing for codon preference and non-randomness in the third position of each codon was consistent with the major ORF in the cDNA being the likely protein-coding ORF. There is a putative Met start codon at position 1089 in the genomic clone. The cDNA homology with respect to the genomic clone begins at nucleotide 1094. Thus Ms26-8.1 does not represent a full length clone and lacks 5 bases up to the putative Met start codon. A database search revealed significant homology to P450 enzymes found in yeast, plants and mammals. P450 enzymes have been widely studied and three characteristic protein domains have been elucidated. The Ms26 protein contains several structural motifs characteristic of eukaryotic P450's, including the heme-binding domain FxxGxRxCxG (domain D; SEQ ID NO: 24), domain A A/GGXD/ETT/S (dioxygen-binding), domain B (steroid-binding), and domain C. The highly conserved heme-binding motif was found in MS26 as FQAGPRICLG (SEQ ID NO: 25), 51 amino acids away from C-terminus. The dioxygen binding domain AGRDTT (SEQ ID NO: 26) was located between amino acids 320-325. The steroid-binding domain was found as LVYLHACVTETLR (SEQ ID NO: 27), amino acids 397-409. The most significant homologous sequence detected in Genebank database is a deduced protein sequence from rice (GeneBank accession number 19071651). The second highest homologous sequence is a putative Arabidopsis P450 gene (CYP704B1) whose function is also unknown. FIG. 14A shows a sequence alignment between CYP704B1 (SEQ ID NO: 12) and Ms26 (SEQ ID NO: 13). Phylogenetic tree analysis of some P450 genes revealed that Ms26 is most closely related to P450s involved in fatty acid omega-hydroxylation found in Arabidopsis thaliana and Vicia sativa (FIG. 14B). The translational frame shift caused in the ms26′-0406 excision mutation is believed to destroy the activity of the heme binding domain, thus resulting in sterility. See the comparison at FIG. 15 (Ms26 cDNA at SEQ ID NO: 14; fertile exon 5 region at SEQ ID NO: 15 and sterile exon 5 region is SEQ ID NO: 16).
Further expression studies were done using the Ms26 cDNA probe against a northern containing mRNA at discrete stages of microsporogenesis. FIG. 6A shows a Northern blot with RNA samples from different tissues including root (1), leaf (2), husk (3), cob (4), ear spikelet (5), silk (6), immature embryo (7) mature embryo (8), and tassel from, fertile plant (9), ms26-m2::Mu8 sterile plant (10), ms26-ref sterile plant (11) and fertile plant (12). A hybridization signal using Ms26 cDNA was detected only in tassel tissues. FIG. 6B shows a Northern blot containing mRNA at discrete stages of microsporogenesis. Hybridization signals using Ms26 cDNA were detected from meiosis II/quartet stage (4) to late-uninucleate stage (10), with the maximal signal being observed from early-uninucleate through late-uninucleate stage (10).
EXAMPLE 6
Identification of Promoter and its Essential Regions
A putative TATA box can be identified by primer extension analysis as described in by Current Protocols in Molecular Biology, Ausubel, F. M. et al. eds; John Wiley and Sons, New York pp. 4.8.1-4.8.5 (1987).
Regulatory regions of anther genes, such as promoters, may be identified in genomic subclones using functional analysis, usually verified by the observation of reporter gene expression in anther tissue and a lower level or absence of reporter gene expression in non-anther tissue. The possibility of the regulatory regions residing “upstream” or 5′ ward of the translational start site can be tested by subcloning a DNA fragment that contains the upstream region into expression vectors for transient expression experiments. It is expected that smaller subgenomic fragments may contain the regions essential for male-tissue preferred expression. For example, the essential regions of the CaMV 19S and 35S promoters have been identified in relatively small fragments derived from larger genomic pieces as described in U.S. Pat. No. 5,352,605.
The selection of an appropriate expression vector with which to test for functional expression will depend upon the host and the method of introducing the expression vector into the host and such methods are well known to one skilled in the art. For eukaryotes, the regions in the vector include regions that control initiation of transcription and control processing. These regions are operably linked to a reporter gene such as UidA, encoding β -glucuronidase (GUS), or luciferase. General descriptions and examples of plant expression vectors and reporter genes can be found in Gruber, et al., “Vectors for Plant Transformation” in Methods in Plant Molecular Biology and Biotechnology; Glick, et al. eds; CRC Press; pp. 89-119; (1993). GUS expression vectors and GUS gene cassettes are commercially available from Clonetech, Palo Alto, Calif., while luciferase expression vectors and luciferase gene cassettes are available from Promega Corporation, Madison, Wis. Ti plasmids and other Agrobacterium vectors are described in Ishida, Y., et al., Nature Biotechnology; Vol. 14; pp. 745-750; (1996) and in U.S. Pat. No. 5,591,616 “Method for Transforming Monocotyledons” (1994).
Expression vectors containing putative regulatory regions located in genomic fragments can be introduced into intact tissues such as staged anthers, embryos or into callus. Methods of DNA delivery include microprojectile bombardment, DNA injection, electroporation and Agrobacterium-mediated gene transfer (see Gruber, et al., “Vectors for Plant Transformation,” in Methods in Plant Molecular Biology and Biotechnology, Glick, et al. eds.; CRC Press; (1993); U.S. Pat. No. 5,591,616; and Ishida, Y., et al., Nature Biotechnology; Vol. 14; pp. 745-750; (1996)). General methods of culturing plant tissues are found in Gruber, et al., supra and Glick, supra.
For the transient assay system, staged, isolated anthers are immediately placed onto tassel culture medium (Pareddy, D. R. and J. F. Petelino, Crop Sci. J.; Vol. 29; pp. 1564-1566; (1989)) solidified with 0.5% Phytagel (Sigma, St. Louis) or other solidifying media. The expression vector DNA is introduced within 5 hours preferably by microprojectile-mediated delivery with 1.2 μm particles at 100-1100 Psi. After DNA delivery, the anthers are incubated at 26° C. upon the same tassel culture medium for 17 hours and analyzed by preparing a whole tissue homogenate and assaying for GUS or for lucifierase activity (see Gruber, et al., supra).
Upstream of the likely translational start codon of Ms26, 1088 bp of DNA was present in the genomic clone ms26-m2::Mu8. Translational fusions via an engineered NcoI site were generated with reporter genes encoding luciferase and β-glucuronidase to test whether this fragment of DNA had promoter activity in transient expression assays of bombarded plant tissues. Activity was demonstrated in anthers and not in coleoptiles, roots and calli, suggesting anther-preferred or anther-specific promoter activity.
A reasonable TATA box was observed by inspection, about 83-77 bp upstream of the translational start codon. The genomic clone ms26-m2::Mu8 thus includes about 1005 bp upstream of the possible TATA box. For typical plant genes, the start of transcription is 26-36 bp downstream of the TATA box, which would give the Ms26 mRNA a 5′-nontranslated leader of about 48-58 nt. The total ms26-m2::Mu8 subgenomic fragment of 1088 bp, including nontranslated leader, start of transcription, TATA box and sequences upstream of the TATA box, was thus shown to be sufficient for promoter activity. See SEQ. ID NO.5. The putative TATA box (TATATCA) is underlined. Thus, the present invention encompasses a DNA molecule having a nucleotide sequence of SEQ ID NO: 5 (or those with sequence identity) and having the function of a male tissue-preferred regulatory region.
Deletion analysis can occur from both the 5′ and 3′ ends of the regulatory region: fragments can be obtained by site-directed mutagenesis, mutagenesis using the polymerase chain reaction, and the like (Directed Mutagenesis: A Practical Approach; IRL Press; (1991)). The 3′ end of the male tissue-preferred regulatory region can be delineated by proximity to the putative TATA box or by 3′ deletions if necessary. The essential region may then be operably linked to a core promoter of choice. Once the essential region is identified, transcription of an exogenous gene may be controlled by the male tissue-preferred region of Ms26 plus a core promoter. The core promoter can be any one of known core promoters such as a Cauliflower Mosaic Virus 35S or 19S promoter (U.S. Pat. No. 5,352,605), Ubiquitin (U.S. Pat. No. 5,510,474), the IN2 core promoter (U.S. Pat. No. 5,364,780), or a Figwort Mosaic Virus promoter (Gruber, et al., “Vectors for Plant Transformation” in Methods in Plant Molecular Biology and Biotechnology; Glick, et al. eds.; CRC Press; pp. 89-119; (1993)). Preferably, the promoter is the core promoter of a male tissue-preferred gene or the CaMV 35S core promoter. More preferably, the promoter is a promoter of a male tissue-preferred gene and in particular, the Ms26 core promoter.
Further mutational analysis, for example by linker scanning, a method well known to the art, can identify small segments containing sequences required for anther-preferred expression. These mutations may introduce modifications of functionality such as in the levels of expression, in the timing of expression, or in the tissue of expression. Mutations may also be silent and have no observable effect.
The foregoing procedures were used to identify essential regions of the Ms26 promoter. After linking the promoter with the luciferase marker gene deletion analysis was performed on the regions of the promoter upstream of the putative TATA box, as represented in FIG. 8. The x-axis of the bar graph indicates the number of base pairs immediately upstream of the putative TATA box retained in a series of deletion derivatives starting from the 5′ end of the promoter. The y-axis shows the normalized luciferase activity as a percent of full-length promoter activity.
As is evident from the graph, approximately 176 bp immediately upstream of the TATA box was sufficient, when coupled to the core promoter (putative TATA box through start of transcription), plus 5′ nontranslated leader, for transient expression in anthers. By contrast, luciferase activity was minimal upon further deletion from the 5′ end to 91 bp upstream of the putative TATA box. This 176 bp upstream of the putative TATA box through the nontranslated leader can be considered a minimal promoter, which is further represented at FIG. 9. The TATA box is underlined. Deletion within the full-length promoter from −176 through −92 relative to the TATA box reduced activity to about 1% of wild type. Deletion of −39 through −8 did not greatly reduce activity. Therefore the −176 to −44 bp region contains an essential region and thus would constitute an upstream enhancer element conferring anther expression on the promoter, which we refer to as an “anther box”.
Linker scanning analysis was conducted across the anther box in 9-10 bp increments. The locations of the linker scanning substitutions in this region are shown in FIG. 9, and the expression levels of the mutants relative to the wild type sequence are shown in FIG. 10. The most drastic effect on transient expression in anthers was observed for mutants LS12 and LS13, in the region 52-71 bp upstream of the putative TATA box. A major effect on transient expression in anthers was also observed for mutants LS06, LS07, LS08 and LS10, within the region 82-131 bp upstream of the putative TATA box. Sequences within the anther box required for wild type levels of transient expression in anthers are thus demonstrated in the −52 to −131 region relative to the putative TATA box, particularly the −52 to −71 region.
EXAMPLE 7
Ms26 Sorghum, Rice and Maize Comparison
As noted above, Ms26 is a male fertility gene in maize. When it is mutated, and made homozygous recessive, male sterility will result. An orthologue of Ms26 was identified in sorghum. The sorghum orthologue of the Ms26 cDNA was isolated by using the maize Ms26 gene primers in a polymerase chain reaction with sorghum tassel cDNA as the template. The resultant cDNA fragment was sequenced by methods described supra and then compared to the Ms26 cDNA from maize. Nucleotide sequence comparisons are set forth in FIG. 11 and show 90% identity. An orthologue from rice was also identified and the predicted coding sequence is SEQ ID NO: 17 and protein is SEQ ID NO: 18. It has one intron less than the maize and sorghum Ms26, and the coding sequences are highly conserved.
Identification of the sorghum and rice promoters was accomplished. FIG. 16 shows an alignment of the Ms26 promoter of corn (SEQ ID NO: 5), sorghum (SEQ ID NO: 19) and rice (SEQ ID NO: 20). The last three bases of the corn promoter shown in the figure is the ATG start of translation.
Alignment as reflected in FIG. 17 of the maize Ms26 protein (SEQ ID NO: 2), rice Ms26 protein(SEQ ID NO: 18) and sorghum Ms26 protein (SEQ ID NO: 4), and a consensus sequence (SEQ ID NO: 35). The comparison of protein sequences shows the protein is highly conserved among the orthologues, with the rice protein sharing 92% similarity and 86% identity when compared to the maize orthologue. The predicted tissue specificity in rice and sorghum is further reflected in a comparison of the Ms26 protein in the sorghum and rice EST database derived from panicle (flower) libraries. Sorghum sequences producing significant alignments (GenBank accession numbers B1075441.1; B1075273.1; B1246000.1; B1246162.1; BG948686.1; B1099541.1 and BG948366.1, among others) all were sequences from immature panicle of sorghum, and sequences showing significant alignment in rice (GenBank accession numbers C73892.1; CR290740.1, among others) were also from rice immature panicle.
As is evident from the above, nucleotide sequences which map to the short arm of chromosome 1 of the Zea mays genome, at the same site as the Ms26 gene, ms26-m2::Mu8 and its alleles, are genes critical to male fertility in plants, that is, are necessary for fertility of a plant, or, when mutated from the sequence found in a fertile plant, cause sterility in the plant.
Thus it can be seen that the invention achieves at least all of its objectives.

## Claims

1. An isolated polynucleotide comprising a sequence encoding the amino acid sequence of SEQ ID NO: 2.