Polycomb repressive complex 2 (PRC2) mediates epigenetic silencing of target genes in animals and plants. In Arabidopsis, PRC2 is required for the cold-induced epigenetic silencing of the FLC 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 FLC. 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 Arabidopsis genome that are modified with H3K27me3. Our work therefore reveals the distinct accessory roles for VEL proteins in conferring cold-induced silencing on FLC, with broad relevance for PRC2 targets generally.

中文翻译：

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拟南芥 VEL 蛋白在 Polycomb 沉默中的独特辅助作用

Polycomb 抑制复合物 2 (PRC2) 介导动物和植物中靶基因的表观遗传沉默。在拟南芥中，寒冷诱导的FLC花抑制基因座表观遗传沉默需要 PRC2，以使开花与春季一致。在此过程中，PRC2 依赖于 VEL 辅助因子，包括组成型表达的 VRN5 和冷诱导的 VIN3。VEL 蛋白在物理上与 PRC2 相关，但它们各自的功能仍不清楚。在这里，我们展示了重组 VRN5 与重构 PRC2 内的多个组件之间的密切关联，这取决于 VRN5 中心结构域的紧凑构象。介导这种紧凑构象的关键残基在整个植物界的 VRN5 直向同源物中是保守的。相反，VIN3 与 VAL1 相互作用，VAL1 是一种直接与FLC结合的转录抑制因子。这些关联对它们在 H3K27me 沉积中的作用产生不同的影响：这两种蛋白都是 H3K27me3 所必需的，但只有 VRN5 是 H3K27me2 所必需的。尽管 VIN3 和 VRN5 最初被定义为春化调节因子，但它们与拟南芥基因组中经过 H3K27me3 修饰的许多靶标相关。因此，我们的工作揭示了 VEL 蛋白在冷诱导FLC沉默中的独特辅助作用，通常与 PRC2 靶点具有广泛的相关性。