• CDK8 is a key subunit of Mediator complex, a large multiprotein complex that is a fundamental part of the conserved eukaryotic transcriptional machinery. However, the biological functions of CDK8 in plant abiotic stress responses remain largely unexplored.
• Here, we demonstrated CDK8 as a critical regulator in the abscisic acid (ABA) signaling and drought response pathways in Arabidopsis. Compared to wild‐type, cdk8 mutants showed reduced sensitivity to ABA, impaired stomatal apertures and hypersensitivity to drought stress. Transcriptomic and chromatin immunoprecipitation analysis revealed that CDK8 positively regulates the transcription of several ABA‐responsive genes, probably through promoting the recruitment of RNA polymerase II to their promoters.
• We discovered that both CDK8 and SnRK2.6 interact physically with an ERF/AP2 transcription factor RAP2.6, which can directly bind to the promoters of RD29A and COLD‐REGULATED 15A (COR15A) with GCC or DRE elements, thereby promoting their expression. Importantly, we also showed that CDK8 is essential for the ABA‐induced expression of RAP2.6 and RAP2.6‐mediated upregulation of ABA‐responsive genes, indicating that CDK8 could link the SnRK2.6‐mediated ABA signaling to RNA polymerase II to promote immediate transcriptional response to ABA and drought signals.
• Overall, our data provide new insights into the roles of CDK8 in modulating ABA signaling and drought responses.

中文翻译：

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CDK8与RAP2.6和SnRK2.6相关联，并在拟南芥中正调节脱落酸信号传导和干旱响应。

• CDK8是介体复合物的关键亚基，介体复合物是一种大型的多蛋白复合物，是保守的真核转录机制的基本组成部分。然而，CDK8在植物非生物胁迫反应中的生物学功能仍未得到充分探索。
• 在这里，我们证明了CDK8是拟南芥中脱落酸（ABA）信号传导和干旱响应途径中的关键调节剂。与野生型相比，cdk8突变体显示出对ABA的敏感性降低，气孔孔径受损以及对干旱胁迫的超敏感性。转录组学和染色质免疫沉淀分析表明，CDK8可能通过促进RNA聚合酶II向其启动子的募集而正调控几种ABA反应基因的转录。
• 我们发现CDK8和SnRK2.6都与ERF / AP2转录因子RAP2.6发生物理相互作用，后者可以直接与带有GCC或DRE元件的RD29A和COLD-REGULATED 15A（COR15A）的启动子结合，从而促进它们的表达。重要的是，我们还表明CDK8对于ABA诱导的RAP2表达至关重要。6和RAP2。6介导的ABA反应基因的上调，表明CDK8可以将SnRK2.6介导的ABA信号与RNA聚合酶II连接，从而促进对ABA和干旱信号的即时转录反应。
• 总体而言，我们的数据为CDK8在调节ABA信号传导和干旱响应中的作用提供了新见解。