MED25 has been implicated as a negative regulator of the abscisic acid (ABA) signaling pathway. However, it is unclear whether other Mediator subunits could associate with MED25 to participate in the ABA response. Here, we used affinity purification followed by mass spectrometry to uncover Mediator subunits that associate with MED25 in transgenic plants. We found that at least 26 Mediator subunits, belonging to the head, middle, tail, and CDK8 kinase modules, were co‐purified with MED25 in vivo. Interestingly, the tail module subunit MED16 was identified to associate with MED25 under both mock and ABA treatments. We further showed that the disruption of MED16 led to reduced ABA sensitivity compared to the wild type. Transcriptomic analysis revealed that the expression of several ABA‐responsive genes was significantly lower in med16 than those in wild type. Furthermore, we discovered that MED16 may possibly compete with MED25 to interact with the key transcription factor ABA INSENSITIVE 5 (ABI5) to positively regulate ABA signaling. Consistently, med16 and med25 mutants displayed opposite phenotypes in ABA response, cuticle permeability, and differential ABI5‐mediated EM1 and EM6 expression. Together, our data indicate that MED16 and MED25 differentially regulate ABA signaling by antagonistically affecting ABI5‐mediated transcription in Arabidopsis.

中文翻译：

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介体尾部模块亚基 MED16 和 MED25 在拟南芥中差异调节脱落酸信号

MED25 被认为是脱落酸 (ABA) 信号通路的负调节因子。然而，尚不清楚其他中介体亚基是否可以与 MED25 相关联以参与 ABA 反应。在这里，我们使用亲和纯化和质谱来发现与转基因植物中的 MED25 相关的介质亚基。我们发现至少 26 个 Mediator 亚基，属于头部、中部、尾部和 CDK8 激酶模块，在体内与 MED25 共同纯化。有趣的是，在模拟和 ABA 处理下，尾部模块亚基 MED16 被鉴定为与 MED25 相关联。我们进一步表明MED16的中断导致与野生型相比降低 ABA 敏感性。转录组学分析显示，med16中几种 ABA 响应基因的表达显着低于野生型。此外，我们发现 MED16 可能与 MED25 竞争与关键转录因子 ABA INSENSITIVE 5 (ABI5) 相互作用，从而正向调节 ABA 信号。一致地，med16和med25突变体在 ABA 反应、角质层通透性和差异ABI5介导的EM1和EM6表达方面显示出相反的表型。总之，我们的数据表明 MED16 和 MED25 通过拮抗 ABI5 介导的转录来差异调节 ABA 信号。拟南芥。