Modulation of the Vernalization Requirement of Hexaploid Wheat by Non-Functional VRN2 Alleles

Plants respond to environmental cues in order to adjust the timing of flowering and ensure reproductive success. In winter wheats a prolonged exposure to low temperatures (vernalization) accelerates the transition from vegetative to reproductive stages. This response is controlled by the VRN2 locus, a long day dependent repressor of flowering. Natural variation in VRN2 is important in the determination of growth habit in diploid wheat and barley, but little is known about the natural variation of VRN2 in hexaploid wheat, except that the VRN-A2 locus is not functional. Here we characterized a non-functional VRN-D2 allele from Aegilops tauschii (progenitor of the D genome) and combined it with a natural deletion of the VRN-B2 locus to develop a hexaploid wheat line with non-functional VRN2 genes. This line carries alleles for winter growth habit at the three VRN1 homoeologous loci.  In the absence of vernalization, plants carrying mutations only in VRN-B2 or VRN-D2 (in addition to the non-functional VRN-A2) flower as late as the plants carrying both functional alleles. By contrast, when non-functional alleles were combined in the three homeologous genomes, heading time was accelerated by more than 100 days (P<2.8E^-07). This hexaploid line with loss-of-function mutations in all three VRN2 loci can be used as tester line to characterize the VRN2 natural variation in hexaploid wheat and it can also be useful tool to determine the adaptative value of this alternative way to generate spring growth habit in hexaploid wheat.