In Arabidopsis thaliana, the cold-induced epigenetic regulation of FLOWERING LOCUS C (FLC) involves distinct phases of Polycomb repressive complex 2 (PRC2) silencing. During cold, a PHD-PRC2 complex metastably and digitally nucleates H3K27me3 within FLC On return to warm, PHD-PRC2 spreads across the locus delivering H3K27me3 to maintain long-term silencing. Here, we studied natural variation in this process in Arabidopsis accessions, exploring Lov-1, which shows FLC reactivation on return to warm, a feature characteristic of FLC in perennial Brassicaceae This analysis identifies an additional phase in this Polycomb silencing mechanism downstream from H3K27me3 spreading. In this long-term silencing (perpetuated) phase, the PHD proteins are lost from the nucleation region and silencing is likely maintained by the read-write feedbacks associated with H3K27me3. A combination of noncoding SNPs in the nucleation region mediates instability in this long-term silencing phase with the result that Lov-1 FLC frequently digitally reactivates in individual cells, with a probability that diminishes with increasing cold duration. We propose that this decrease in reactivation probability is due to reduced DNA replication after flowering. Overall, this work defines an additional phase in the Polycomb mechanism instrumental in natural variation of silencing, and provides avenues to dissect broader evolutionary changes at FLC.

中文翻译：

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非编码 SNP 影响 Polycomb 沉默的不同阶段，从而破坏拟南芥 FLC 的长期表观遗传记忆。


在拟南芥中，寒冷诱导的 FLOWERING LOCUS C (FLC) 表观遗传调控涉及 Polycomb 抑制复合物 2 (PRC2) 沉默的不同阶段。在寒冷期间，PHD-PRC2 复合物在 FLC 内以亚稳态和数字方式使 H3K27me3 成核。当恢复温暖时，PHD-PRC2 在整个基因座上扩散，提供 H3K27me3 以维持长期沉默。在这里，我们研究了拟南芥种质中这一过程的自然变异，探索了Lov-1，它显示了FLC在返回温暖时重新激活，这是多年生十字花科植物FLC的一个特征。该分析确定了H3K27me3传播下游的多梳沉默机制中的另一个阶段。在这个长期沉默（永久）阶段，PHD 蛋白从成核区域丢失，沉默可能由与 H3K27me3 相关的读写反馈维持。成核区域中的非编码 SNP 组合介导了长期沉默阶段的不稳定性，导致 Lov-1 FLC 在单个细胞中频繁以数字方式重新激活，其概率随着冷持续时间的增加而减小。我们认为重新激活概率的降低是由于开花后 DNA 复制减少所致。总的来说，这项工作定义了 Polycomb 机制中的一个额外阶段，有助于沉默的自然变异，并提供了剖析 FLC 更广泛进化变化的途径。