PRC2 recruitment and H3K27me3 deposition at <i>FLC</i> require FCA binding of <i>COOLAIR</i>

Abstract

The cold-induced antisense transcript <i>COOLAIR</i> represses <i>FLOWERING LOCUS C</i> (<i>FLC</i>) transcription with increased H3K27me3 and decreased H3K36me3 levels in response to cold temperatures. However, the molecular connection between <i>COOLAIR</i> and histone modification factors in the absence of cold treatment remains unclear. We report that the RNA binding protein FCA interacts with the PRC2 subunit CURLY LEAF (CLF) and binds nascent <i>COOLAIR</i> transcripts to allow deposition of H3K27me3 at <i>FLC</i>. Loss of <i>COOLAIR</i> function results in a reduction in FCA and CLF enrichment, which, in turn, decreases H3K27me3 levels at <i>FLC</i>. The <i>Arabidopsis</i> protein phosphatase SSU72 physically interacts with the RRM1 motif of FCA to antagonize FCA binding with <i>COOLAIR</i>. Mutations in <i>SSU72</i> caused early flowering, reduced <i>FLC</i> transcription, increased CLF enrichment and H3K27me3, and enhanced affinity between FCA and <i>COOLAIR</i>. Our results suggest that FCA binding of <i>COOLAIR</i> and SSU72 is critical for PRC2 enrichment and H3K27me3 deposition in <i>Arabidopsis</i>.