| Description |
The phytohormone abscisic acid (ABA) induces senescence and facilitates nutrient reuse, which are essential for increasing stress tolerance. Senescence controls plant aging and is closely associated with crop yield and quality1-3. It is a complicated process finely tuned by multiple layers of control. A significant proportion of ABA-responsive genes and cis-elements are targeted by H3K27me3 modification that is mediated by Polycomb group proteins (PcGs)4,5; however, the interplay between the major epigenetic machinery and the central stress hormone is poorly understood. Both pathways influence the transcription of thousands of genes, and the dynamic and quantitative epigenomic and transcriptomic changes cannot be characterized with high confidence. This issue is further complicated by the redundant roles of PcG components 6. This article revealed an intriguing mechanism of the interplay between ABA and PcG in regulating plant senescence, based on the integration of genetic evidence and quantitative comparison of epigenomic data derived from a purpose-developed computational model. We observed that >30% of ABA-induced genes are up-regulated in a double mutant of H3K27me3 methyltransferases CLF and SWN; and the double mutant, but not single-gene mutants, is hyper-sensitive to ABA treatment. Importantly, ABA-triggered H3K27me3 reduction preferentially occurred in regions around senescence-associated genes (SAGs), which are redundantly repressed by CLF and SWN in normal conditions. Furthermore, we revealed that the presence of H3K27me3 surrounding SAGs does not block ABA-induced SAG expression, but rather limits the extent of the induction, thereby preventing an over-sensitive response within a dynamic environment. These findings may serve as a paradigm for the crosstalk between the rapid-effect of phytohormone and the long-term effect of epigenetic machinery in regulating plant environmental responses through modulations of the senescence process.
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