LC2 and OsVIL2 promote rice flowering by photoperoid-induced epigenetic silencing of OsLF.

Proper flowering time is essential for plant reproduction. Winter annual Arabidopsis thaliana needs vernalization before flowering, during which AtVILs (VIN3 and VRN5, components of PRC2 complex) mediate the H3K27 tri-methylation at the FLC locus (a floral repressor) to repress the FLC expression and hence to induce flowering. However, how VILs (VIL, VERNALIZATION INSENSITIVE 3-LIKE) function in rice is unknown. Here we demonstrated that rice LC2 (OsVIL3) and OsVIL2 (two OsVILs, possible components of PRC2 complex) promote rice flowering. Our results showed that expressions of LC2 and OsVIL2 are induced by SD (short-day) conditions and both lc2 mutant and OsVIL2-RNAi lines display delayed heading date, consistent with the reduced expression levels of Hd1 and Hd3a. Interestingly, LC2 binds to the promoter region of a floral repressor OsLF and represses the OsLF expression via H3K27 tri-methylation modification. In addition, OsLF directly regulates the Hd1 expression through binding to Hd1 promoter. These results first demonstrated that the putative PRC2 in rice is involved in photoperiod flowering regulation, which is different from that of Arabidopsis, and revealed that LC2 binds the promoter region of target gene, presenting a possible mechanism of the recruitment process of PRC2 complex to its target genes. The studies provide informative clues on the epigenetic control of rice flowering.