Knockdown of SAMS genes encoding S-adenosyl-l-methionine synthetases causes methylation alterations of DNAs and histones and leads to late flowering in rice

S-Adenosyl-l-methionine synthetase (SAMS) [EC 2.5.1.6] catalyzes to produce SAM (S-adenosyl-l-methionine), a universal methyl group donor in biochemical reactions in cells. However, less is known how SAMS controls plant development. Here, we demonstrate that OsSAMS1, 2 and 3 are essential for histone H3K4me3 and DNA methylation to regulate gene expression related to flowering in Oryza sativa. RNA interference (RNAi) transgenic rice with downregulated transcripts of OsSAMS1, 2 and 3 showed pleiotropic phenotypes, including dwarfism, reduced fertility, delayed germination, as well as late flowering. Delayed germination was largely rescued by application of SAM in the knockdown lines. Knockdown of OsSAMS1, 2 and 3 led to distinguished late flowering and greatly reduced the expression of the flowering key genes, Early heading date 1 (Ehd1), Hd3a and RFT1 (rice FT-like genes). Moreover, the histone H3K4me3 and symmetric DNA methylation at these genes were greatly reduced. Thus, SAM deficiency suppressing DNA and H3K4me3 transmethylations at flowering key genes led to a late-flowering phenotype in rice. This information could help elucidate the mechanism of epigenetic control flowering transition.