OsEMF2b Acts as a Regulator of Flowering Transition and Floral Organ Identity by Mediating H3K27me3 Deposition at OsLFL1 and OsMADS4 in Rice

Flowering transition and floral organ development influence plant propagation and crop yield. Polycomb-group (PcG) gene EMF2 restrains flowering by suppressing floral organ identity genes as an epigenetic regulator in Arabidopsis. Here, we identified that OsEMF2b, a homologue of EMF2, acted as a regulator of flowering transition and floral organ identity in rice. The OsEMF2b T-DNA insertion mutations and RNA interference transgenic plants cause late flowering, whereas OsEMF2b overexpressing lines result in early flowering. The transcript levels of genes involved in rice flowering pathway differ in wild-type plants and osemf2b mutants. The transcripts of Ehd1, Hd3a, and RFT1 decrease, whereas the expression level of OsLFL1 increases in the osemf2b mutants under short-day and long-day conditions. These results indicated that OsEMF2b functioned as the upregulator of Ehd1, Hd3a, and RFT1 and the downregulator of OsLFL1 during floral induction. Quantitative RT-PCR assay indicated that OsEMF2b regulated the transcript levels of floral homeotic A-, B-, C-, D-, and E-class genes and participated in floral organ development in rice. Chromatin immunoprecipitation analyses showed that OsEMF2b was directly associated with OsLFL1 and OsMADS4, such that the H3K27me3 was enriched on these target genes chromatin in WT but not in the OsEMF2b RNAi plants. Our results demonstrate that OsEMF2b promotes flowering through direct suppressing of the OsLFL1 expression (a suppressor of flowering) via a mechanism distinct from Arabidopsis.