Positional Cloning of the Wheat Vernalization Gene VRN-D4 Reveals the Origin of Spring Growth Habit in Ancient Hexaploid Wheats from India

In winter wheat a prolonged exposure to low temperatures (vernalization) accelerates the transition from vegetative to reproductive stages. VRN-D4 locus is known to control the vernalization response but has not yet been described at molecular level.  In our study we have mapped VRN-D4 in the centromeric region of chromosome 5DS.  Sequencing of 1.2Mb of the VRN-D4 candidate gene region revealed a single gene. Allelic variation at the VRN-D4-candidate gene correlated with VRN-D4 alleles for spring and winter growth habit. Expression profiles of the VRN-D4-candidate during development showed that it is highly expressed in the leaves from early developmental stages, and this expression was correlated with the down-regulation of the VRN2 flowering repressor and the upregulation of the FT flowering promoter. An EMS TILLING mutant of the VRN-D4-candidate gene resulting in a single amino acid change delayed flowering by 10 days. We discuss evidence supporting an early origin of the VRN-D4 spring allele in the Indian subcontinent.