Identification of Natural Null Alleles at Three VRN-2 Genes and Their Potential Application in Hexaploid Wheat.

Winter wheat is sown in autumn and requires exposure to cold temperatures in the winter season to flower in the next spring season. The low-temperature requirement to accelerate flowering in winter wheat is called vernalization. A dominant allele of the vernalization gene Vrn-2 is the wild type conferring winter growth habit, whereas a recessive vrn-2 allele confers spring growth habit. The recessive vrn-2 allele is mutated due to a deletion of the complete gene (a null form) or alternation of a key amino acid in the VRN-2 protein (a nonfunctional form) in diploid wheat or tetraploid wheat. Gene VRN-2 is also called ZCCT due to the presence of a zinc finger and a CCT domain in its protein. There are two paralogous ZCCT genes at the VRN-2 locus in diploid T. monococcum and three paralogous ZCCT genes on each of A and B genomes in tetraploid wheat. However, allelic variation for VRN-2 has not been described so far for hexaploid wheat, which is likely due to a rare occurrence of spring growth habit that is caused by a null or nonfunctional allele at all three VRN-2 genes in a given cultivar. In this present study, we discovered a null ZCCT-1 allele at each of the VRN-2 loci on A, B, and D genomes in hexaploid wheat. These mutant materials would facilitate developing spring wheat variety by introducing the three null alleles into a single line, determining non-functional and functional alleles by various combinations of any two null alleles with another unknown allele, investigating dosage effects of functional alleles on vernalization requirement in winter cultivars, and identifying interacting proteins with ZCCT-1 proteins in hexaploid wheat. The markers for the three VRN-2 genes will accelerate application of these genes in wheat molecular breeding programs.