DEFORMED FLORAL ORGAN1 (DFO1) regulates floral organ identity by epigenetically repressing the expression of OsMADS58 in rice (Oryza sativa).

Floral organ identity in plants is controlled by floral homeotic A/B/C/D/E-class genes. In Arabidopsis thaliana, several epigenetic repressors that regulate these floral organ identity genes have been characterized. However, the roles of epigenetic factors in rice floral development have not been explored in detail. Here, we report the identification and functional characterization of a rice epigenetic repressor, DEFORMED FLORAL ORGAN1 (DFO1) gene, which causes abnormal floral morphology when mutated. We isolated dfo1 by mapping, and confirmed its function by rescue experiments, combined with genetic, cytological and molecular biological analysis. We showed that DFO1 is constitutively expressed and encodes a nuclear-localized protein. Mutation of DFO1 causes the ectopic expression of C-class genes in the dfo1-1 mutant, and overexpression of OsMADS58, a C-class gene, phenocopies the dfo1 mutants. In vitro and in vivo experiments demonstrated that DFO1 interacts with the rice polycomb group (PcG) proteins (OsMSI1 and OsiEZ1). Remarkably, trimethylation of histone H3 lysine 27, a mark of epigenetic repression, is significantly reduced on OsMADS58 chromatin in the dfo1-1 mutant. Our results suggest that DFO1 functions in maintaining rice floral organ identity by cooperating with PcG proteins to regulate the H3K27me3-mediated epigenetic repression on OsMADS58.