The DNA Methylation Profile of the VRN-1A Gene Changes Following Vernalization in Hexaploid Wheat

A major phenomenon in the wheat plant life cycle is the transition from the vegetative to the reproductive stage. Some wheat varieties (referred to as “winter type”) require a long exposure to low temperatures to achieve this transition, a phenomenon known as vernalization. While several genes are involved in flowering time, allelic variation of VRN-1 is one of the main genetic sources of wheat vernalization requirement. In hexaploid common wheat (AABBDD), which carries three copies of VRN-1 (designated VRN-1A, VRN-1B, and VRN-1D), the presence of a dominant (Vrn) allele is sufficient to confer a spring phenotype. On the other hand, vernalization is environmentally-induced, and could therefore be driven by an epigenetic process. To investigate whether DNA methylation of VRN-1A could be involved in the response of wheat to vernalization, we analyzed the DNA methylation profile of this gene among various wheat varieties carrying diverse VRN-1 alleles, which were submitted or not to a 45 days cold treatment. PCR-amplification on bisulfite-treated DNA revealed heterogeneous repartition of methylated cytosines along the gene. Methylation profile was unvariable for most regions of the gene in both treatment conditions. However, two regions located within the gene body were shown to increase in methylation at specific sites following vernalization, thus suggesting that vernalization may induce methylation of these regions. The role of such gene-body methylation pattern in response to vernalization is still unknown, and its characterization will help unraveling new processes of epigenetic regulation.