The histone variant H3.3 promotes the active chromatin state to repress flowering in Arabidopsis

We report that H3.3 stimulates the expression of FLC and its homologs, and promotes the active histone modifications at their loci. FRI directly interacts with the H3.3 chaperone HIRA and elevates H3.3 deposition towards the FLC 3’ region. The enriched H3.3 facilitates FLC 3’ end interaction with the 5’ end, promoting active histone modifications around the transcription start site (TSS) of FLC. In contrast, though coordinately activate FLC expression; H3.3 and H2A.Z antagonize each other at the FLC chromatin. In addition to FLC and its homologs, H3.3 is required for H3K4me3 at a subset of especially short genes. Our findings reveal the important function of H3.3 in the regulation of the active chromatin state, which enhances FLC transcription and floral repression HTR5 distribution in seedlings