Distinct accessory roles of<i>Arabidopsis</i>VEL proteins in Polycomb silencing

Abstract

Polycomb repressive complex 2 (PRC2) mediates epigenetic silencing of target genes in animals and plants. In <i>Arabidopsis</i>, PRC2 is required for the cold-induced epigenetic silencing of the <i>FLC</i> floral repressor locus to align flowering with spring. During this process, PRC2 relies on VEL accessory factors, including the constitutively expressed VRN5 and the cold-induced VIN3. The VEL proteins are physically associated with PRC2, but their individual functions remain unclear. Here, we show an intimate association between recombinant VRN5 and multiple components within a reconstituted PRC2, dependent on a compact conformation of VRN5 central domains. Key residues mediating this compact conformation are conserved among VRN5 orthologs across the plant kingdom. In contrast, VIN3 interacts with VAL1, a transcriptional repressor that binds directly to <i>FLC</i> These associations differentially affect their role in H3K27me deposition: Both proteins are required for H3K27me3, but only VRN5 is necessary for H3K27me2. Although originally defined as vernalization regulators, VIN3 and VRN5 coassociate with many targets in the <i>Arabidopsis</i> genome that are modified with H3K27me3. Our work therefore reveals the distinct accessory roles for VEL proteins in conferring cold-induced silencing on <i>FLC</i>, with broad relevance for PRC2 targets generally.