Leaf senescence is a highly-programmed developmental process during the plant life cycle. ABA plays an important role in leaf senescence. However, the mechanism underlying ABA-mediated leaf senescence, particularly the upstream epigenetic regulatory network, remains largely unclear. Here, we identified that SlJMJ4, a Jumonji C (jmjC) domain-containing protein in tomato, specifically demethylates di- and tri-methylations of lysine 27 of histone H3 (H3K27) in vitro and in vivo. Overexpression of SlJMJ4 results in premature senescence phenotype and promotes dark- and ABA-induced leaf senescence in tomato. Under dark condition, SlJMJ4-promoted leaf senescence is associated with upregulated expression of transcription factors (SlORE1 and SlNAP2) and senescence-associated genes (SlSAG113, SlSAG12) via removal of H3K27me3. In responses to ABA, overexpression of SlJMJ4 increases its binding at the loci of SlORE1, SlNAP2, SlSAG113, SlSAG12, SlABI5 and SlNCED3 and decreases their H3K27me3 levels, and therefore activates their expression and mediates ABA-induced leaf senescence in tomato. Taken together, these results demonstrate that SlJMJ4 plays a positive role in leaf senescence in tomato and is implicated in ABA-induced leaf senescence by binding to many key genes related to ABA synthesis and signaling, transcription regulation and senescence and hence promoting their H3K27me3 demethylation.

中文翻译：

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组蛋白 H3K27 去甲基化酶 SlJMJ4 促进暗和 ABA 诱导的番茄叶片衰老。

叶片衰老是植物生命周期中高度程序化的发育过程。ABA在叶片衰老中起重要作用。然而，ABA 介导的叶片衰老的机制，特别是上游的表观遗传调控网络，在很大程度上仍不清楚。在这里，我们发现 SlJMJ4 是番茄中一种含有 Jumonji C (jmjC) 结构域的蛋白质，可在体外和体内特异性地使组蛋白 H3 (H3K27) 的赖氨酸 27 的二甲基化和三甲基化去甲基化。SlJMJ4 的过表达导致番茄过早衰老表型并促进暗和 ABA 诱导的番茄叶片衰老。在黑暗条件下，SlJMJ4 促进的叶片衰老与通过去除 H3K27me3 上调转录因子（SlORE1 和 SlNAP2）和衰老相关基因（SlSAG113、SlSAG12）的表达有关。作为对 ABA 的回应，SlJMJ4 的过表达增加了其在 SlORE1、SlNAP2、SlSAG113、SlSAG12、SlABI5 和 SlNCED3 位点的结合并降低了它们的 H3K27me3 水平，因此激活了它们的表达并介导了 ABA 诱导的番茄叶片衰老。总之，这些结果表明，SlJMJ4 在番茄叶片衰老中起积极作用，并通过与许多与 ABA 合成和信号传导、转录调控和衰老相关的关键基因结合，从而促进其 H3K27me3 去甲基化，从而参与 ABA 诱导的叶片衰老。