Plants often experience recurrent stressful events, for example, during heat waves. They can be primed by heat stress (HS) to improve the survival of more severe heat stress conditions. At certain genes, sustained expression is induced for several days beyond the initial heat stress. This transcriptional memory is associated with hyper-methylation of histone H3 lysine 4 (H3K4me3), but it is unclear how this is maintained for extended periods. Here, we determined histone turnover by measuring the chromatin association of HS-induced histone H3.3. Genome-wide histone turnover was not homogenous; in particular, H3.3 was retained longer at heat stress memory genes compared to HS-induced non-memory genes during the memory phase. While low nucleosome turnover retained H3K4 methylation, methylation loss did not affect turnover, suggesting that low nucleosome turnover sustains H3K4 methylation, but not vice versa. Together, our results unveil the modulation of histone turnover as a mechanism to retain environmentally mediated epigenetic modifications.

中文翻译：

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组蛋白保留在植物热应激诱导的转录记忆过程中保留表观遗传标记


植物经常经历反复出现的应激事件，例如在热浪期间。它们可以通过热应激（HS）来启动，以提高在更严重的热应激条件下的生存能力。对于某些基因，在最初的热应激后几天内会诱导持续表达。这种转录记忆与组蛋白 H3 赖氨酸 4 (H3K4me3) 的过度甲基化有关，但尚不清楚这种现象如何长期维持。在这里，我们通过测量 HS 诱导的组蛋白 H3.3 的染色质关联来确定组蛋白周转。全基因组组蛋白周转不均匀；特别是，在记忆阶段，与 HS 诱导的非记忆基因相比，H3.3 在热应激记忆基因上的保留时间更长。虽然低核小体周转率保留了 H3K4 甲基化，但甲基化丢失并不影响周转率，这表明低核小体周转率维持 H3K4 甲基化，但反之则不然。总之，我们的结果揭示了组蛋白周转的调节作为保留环境介导的表观遗传修饰的机制。