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OsVIL1 controls flowering time in rice by suppressing OsLF under short days and by inducing Ghd7 under long days.
KEY MESSAGE: OsVIL1 is associated with a PRC2-like complex through its fibronectin type III domain to activate flowering by suppressing OsLF under SD and delay flowering by inducing Ghd7 under LD. Polycomb repressive complex 2 (PRC2) inhibits the expression of target genes by modifying histone proteins. Although several genes that epigenetically regulate flowering time have been identified in Arabidopsis thaliana and rice (Oryza sativa), the molecular mechanism by which PRC2 affects flowering time has not been well understood in rice. We investigated the role of Oryza sativa VERNALIZATION INSENSITIVE 3-LIKE 1 (OsVIL1), which is homologous to the flowering promoter OsVIL2. The reduction in OsVIL1 expression by RNA interference (RNAi) caused a late flowering phenotype under short days (SD). In the RNAi lines, OsLF expression was increased, but transcripts of Early heading date 1 (Ehd1), Heading date 3a (Hd3a), and RICE FLOWERING LOCUS T 1 (RFT1) were reduced. By contrast, OsVIL1-overexpressing (OX) transgenic lines displayed an early flowering phenotype under SD. Levels of OsLF transcript were reduced while those of Ehd1, Hd3a, and RFT1 were enhanced in the OX lines. Under long days (LD), the OsVIL1-OX lines flowered late and Grain number, plant height, and heading date 7 (Ghd7) expression was higher. We also demonstrated that the plant homeodomain region of OsVIL1 binds to native histone H3 in vitro. Our co-immunoprecipitation assays showed that OsVIL1 interacts with OsVIL2 and that the fibronectin type III domain of OsVIL1 is associated with O. sativa EMBRYONIC FLOWER 2b (OsEMF2b). We propose that OsVIL1 forms a PRC2-like complex to induce flowering by suppressing OsLF under SD but delay flowering by elevating Ghd7 expression under LD.
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