转录中介体 (Mediator)是由多个在进化上高度保守的亚基组成的蛋白复合物。在基因转录过程中，转录中介体分别与基因特异的转录因子和RNA聚合酶II相互作用, 广泛参与二者之间的信息传递，被称为真核生物基因转录的中央控制器。在植物激素信号转导研究中，人们主要关注激素特异的转录因子的作用，但对于转录中介体的功能及作用机理所知甚少。
李传友实验室最近的研究揭示了拟南芥转录中介体复合物在茉莉酸信号途径中的功能及作用机理。MYC2是茉莉酸信号通路的核心转录因子，调控茉莉酸反应的多个方面，包括根生长、机械受伤反应和抗病反应等。遗传学研究表明拟南芥转录中介体的一个亚基MED25是茉莉酸信号途径的正向调控元件，MED25突变后影响了MYC2的功能及茉莉酸诱导的基因表达。一系列生化证据表明，在茉莉酸信号转导过程中，MED25以茉莉酸依赖的方式被募集到MYC2靶标基因的启动子区域，特异性地与MYC2的转录激活区相互作用并正向影响其转录调控功能。更深入的研究表明，在茉莉酸诱导的基因转录过程中，MED25的一个重要作用是把RNA聚合酶II及相关的转录辅助因子招募到MYC2靶标基因的启动子区域，进而精细调节MYC2的转录调控活性。该研究同时发现MED25通过与转录因子ABI5相互作用负向调控脱落酸介导的基因表达。令人感兴趣的是，MED25对脱落酸信号通路的影响是通过负向调控ABI5蛋白的降解过程实现的。
这项研究表明作为转录中介体的一个亚基，MED25能够和多种信号途径的转录因子相互作用，从而以截然不同的方式调控不同植物激素的信号转导，这些发现为深入认识植物激素的转录调控机理提供了一个新的切入点。相关研究成果于2012年7月20日在线发表在Plant Cell（DOI:10.1105/tpc.112.098277）上。李传友实验室的陈蓉和蒋红玲为该论文的共同第一作者。该项工作得到农业部、科技部和国家自然科学基金委的资助。（生物谷Bioon.com）
doi:10.1105/tpc.112.098277
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The Arabidopsis Mediator Subunit MED25 Differentially Regulates Jasmonate and Abscisic Acid Signaling through Interacting with the MYC2 and ABI5 Transcription Factors[C][W][OA]
Rong Chen1, Hongling Jiang1, Lin Li, Qingzhe Zhai, Linlin Qi, Wenkun Zhou, Xiaoqiang Liu, Hongmei Li2, Wenguang Zheng3, Jiaqiang Sun and Chuanyou Li4
Transcriptional regulation plays a central role in plant hormone signaling. At the core of transcriptional regulation is the Mediator, an evolutionarily conserved, multisubunit complex that serves as a bridge between gene-specific transcription factors and the RNA polymerase machinery to regulate transcription. Here, we report the action mechanisms of the MEDIATOR25 (MED25) subunit of the Arabidopsis thaliana Mediator in regulating jasmonate- and abscisic acid (ABA)–triggered gene transcription. We show that during jasmonate signaling, MED25 physically associates with the basic helix-loop-helix transcription factor MYC2 in promoter regions of MYC2 target genes and exerts a positive effect on MYC2-regulated gene transcription. We also show that MED25 physically associates with the basic Leu zipper transcription factor ABA-INSENSITIVE5 (ABI5) in promoter regions of ABI5 target genes and shows a negative effect on ABI5-regulated gene transcription. Our results reveal that underlying the distinct effects of MED25 on jasmonate and ABA signaling, the interaction mechanisms of MED25 with MYC2 and ABI5 are different. These results highlight that the MED25 subunit of the Arabidopsis Mediator regulates a wide range of signaling pathways through selectively interacting with specific transcription factors.
