轉(zhuǎn)錄中介體 (Mediator)是由多個在進化上高度保守的亞基組成的蛋白復合物,。在基因轉(zhuǎn)錄過程中,，轉(zhuǎn)錄中介體分別與基因特異的轉(zhuǎn)錄因子和RNA聚合酶II相互作用, 廣泛參與二者之間的信息傳遞,，被稱為真核生物基因轉(zhuǎn)錄的中央控制器,。在植物激素信號轉(zhuǎn)導研究中,，人們主要關(guān)注激素特異的轉(zhuǎn)錄因子的作用,，但對于轉(zhuǎn)錄中介體的功能及作用機理所知甚少,。
李傳友實驗室最近的研究揭示了擬南芥轉(zhuǎn)錄中介體復合物在茉莉酸信號途徑中的功能及作用機理,。MYC2是茉莉酸信號通路的核心轉(zhuǎn)錄因子，調(diào)控茉莉酸反應(yīng)的多個方面,，包括根生長,、機械受傷反應(yīng)和抗病反應(yīng)等。遺傳學研究表明擬南芥轉(zhuǎn)錄中介體的一個亞基MED25是茉莉酸信號途徑的正向調(diào)控元件,，MED25突變后影響了MYC2的功能及茉莉酸誘導的基因表達,。一系列生化證據(jù)表明，在茉莉酸信號轉(zhuǎn)導過程中,，MED25以茉莉酸依賴的方式被募集到MYC2靶標基因的啟動子區(qū)域,，特異性地與MYC2的轉(zhuǎn)錄激活區(qū)相互作用并正向影響其轉(zhuǎn)錄調(diào)控功能。更深入的研究表明，在茉莉酸誘導的基因轉(zhuǎn)錄過程中,，MED25的一個重要作用是把RNA聚合酶II及相關(guān)的轉(zhuǎn)錄輔助因子招募到MYC2靶標基因的啟動子區(qū)域,，進而精細調(diào)節(jié)MYC2的轉(zhuǎn)錄調(diào)控活性。該研究同時發(fā)現(xiàn)MED25通過與轉(zhuǎn)錄因子ABI5相互作用負向調(diào)控脫落酸介導的基因表達,。令人感興趣的是,，MED25對脫落酸信號通路的影響是通過負向調(diào)控ABI5蛋白的降解過程實現(xiàn)的。
這項研究表明作為轉(zhuǎn)錄中介體的一個亞基,，MED25能夠和多種信號途徑的轉(zhuǎn)錄因子相互作用,，從而以截然不同的方式調(diào)控不同植物激素的信號轉(zhuǎn)導，這些發(fā)現(xiàn)為深入認識植物激素的轉(zhuǎn)錄調(diào)控機理提供了一個新的切入點,。相關(guān)研究成果于2012年7月20日在線發(fā)表在Plant Cell（DOI:10.1105/tpc.112.098277）上,。李傳友實驗室的陳蓉和蔣紅玲為該論文的共同第一作者。該項工作得到農(nóng)業(yè)部,、科技部和國家自然科學基金委的資助,。（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.
