Liza J. Conrad, Imtiyaz Khanday, Cameron Johnson, Emmanuel Guiderdoni, Gynheung An, Usha Vijayraghavan, Venkatesan Sundaresan

The Polycomb Repressive Complex 2 (PRC2) represses transcriptional activity of target genes through trimethylation of Lysine 27 of Histone H3. The functions of the plant PRC2 have been chiefly described in Arabidopsis but specific functions in other plant species, especially the cereals, are still largely unknown. Here we characterize mutants in the rice EMF2B gene, an ortholog of the Arabidopsis EMBRYONIC FLOWER2 (EMF2) gene. Loss of EMF2B in rice results in complete sterility, and mutant flowers have severe floral organ defects and indeterminacy that resemble loss of function mutants in E-function floral organ specification genes. Transcriptome analysis identified the E-function genes OsMADS1, OsMADS6 and OsMADS34 as differentially expressed in the emf2b mutant compared to wild type. OsMADS1 and OsMADS6 known to be required for meristem determinacy in rice, have reduced expression in the emf2b mutant, whereas OsMADS34 which interacts genetically with OsMADS1 was ectopically expressed. Chromatin immunoprecipitation for H3K27me3 followed by qRT-PCR showed that all three genes are presumptive targets of the PRC2 in the meristem. Therefore, in rice, and possibly other cereals, the PRC2 appears to play a major role in floral meristem determinacy through modulation of the expression of E-function genes. This article is protected by copyright. All rights reserved.