CDK8调控ABA信号转导和干旱胁迫应答的分子机制研究

As an important member of mediator complex, CDK8 is known to be involved in the regulation of flower organ development and resistance to pathogen invasion in plants. However, the roles of CDK8 in plant hormone signal transduction pathways and abiotic stress responses remain unclear. We recently found that cdk8 mutants showed reduced sensitivity to ABA, faster water loss and increased sensitivity to drought stress. We further used mass spectrometry approach to study the functional complex components of CDK8 and revealed that CDK8 and SnRK2.6 exist in a protein complex. Yeast two-hybrid (Y2H) and luciferase complementation imaging (LCI) experiments demonstrated that CDK8 can interact with SnRK2.2/2.3/2.6. Moreover, several ABA induced gene expressions were suppressed in cdk8 mutants. This project intends to illustrate the interactions and regulatory mechanism between CDK8 and SnRK2.2/2.3/2.6, identify the phosphorylated substrate of CDK8, and reveal the downstream and specific target genes of CDK8 and SnRK2.2/2.3/2.6. This study will uncover the molecular mechanism by which CDK8 regulates ABA signaling transduction and drought stress response, and will also help identify new pathways that regulate the transcription of downstream genes in the ABA signaling pathway.

CDK8作为中介因子复合体中的一个重要成员，已知参与调控植物花器官发育和抵御病原菌入侵等过程。然而它在重要植物激素信号转导途径和非生物胁迫应答中的功能尚不明确。我们近期研究发现CDK8的功能缺失明显降低植物对ABA的敏感性，却增加叶片失水速率和对干旱胁迫的敏感性。质谱分析CDK8在植物体内的结合蛋白时发现CDK8和SnRK2.6共存于一个蛋白复合体，酵母双杂交和荧光素酶互补实验显示CDK8与SnRK2.2/2.3/2.6确实存在互作，并发现CDK8的突变明显抑制了多个ABA响应基因的诱导表达。本项目拟重点研究CDK8与SnRK2.2/2.3/2.6之间的互作调节机制，鉴定CDK8的磷酸化底物，并解析CDK8和SnRK2.2/2.3/2.6共同和特异调控的下游基因。该研究有望揭示CDK8调控ABA信号转导通路和干旱胁迫应答机制，并有助于发现参与调控ABA信号通路下游基因转录的新途径。

中介因子复合体是真核生物RNA聚合酶II转录机器的重要组成部分，起着连接不同转录因子和RNA聚合酶II的桥梁作用，参与了几乎所有的基因转录调控。CDK8作为中介因子复合体中激酶亚基的一个重要成员，已知参与调控植物花器官发育和植物免疫响应等过程。然而它在植物激素信号通路和非生物胁迫应答中的功能尚不明确。我们近期的研究发现CDK8的功能缺失明显降低了植物对ABA的敏感性，增加了叶片失水速率和气孔开度，以及对干旱胁迫的敏感性；而CDK8的过表达植株材料增加了植物对ABA的敏感性和耐旱能力。质谱分析和酵母筛库发现CDK8可以与ERF类转录因子RAP2.6互作，并通过RAP2.6与ABA信号通路的关键激酶SnRK2.6共存于一个蛋白复合体；转录组测序和基因表达实验发现CDK8的突变抑制了ABA响应基因的表达，ChIP和EMSA实验接着证实RAP2.6可以直接结合ABA响应基因COR15A和RD29A启动子的GCC和DRE元件，并且CDK8对于RNA聚合酶II招募到这些基因的启动子也起着必要的调节作用。遗传学实验进一步表明RAP2.6的过表达材料增加了植物对ABA和甘露醇的敏感性，以及造成ABA响应基因表达的上调。综上，该研究成果发现了ABA信号通路的核心组分SnRK2.6与RNA聚合酶II转录机器之间的紧密联系，有助于深入理解植物快速响应外界环境信号的转录调控机制。