源自叶绿体被膜的胞吞途径调节脱落酸信号和干旱胁迫应答的机制研究

ABA plays fundamental roles in plant response to drought. Clathrin-mediated endocytosis (CME) and vesicle trafficking, which are responsible for intracellular transportation and signal transduction between different organelles, are also involved in ABA signaling pathway. However, little is known about whether there is a CME from the envelope membrane of chloroplasts. Our previous studies identified a novel gene termed as Chloroplast Vesiculation (CV) in Arabidopsis. CV gene is activated by water stress and ABA. CV protein is localized in the envelope membrane of chloroplasts and can induce vesicle formation from chloroplast. The CV-containing vesicles (CCVs) carrying chloroplast proteins depart from chloroplasts and are transported to the vacuole for protein degradation. The mechanisms of CV-induced chloroplast vesiculation remain unknown. Our recent studies indicated that CV could interact with clathrin heavy chain (CHC2) and recruit endocytosis machinery to generate vesicles from chloroplasts. In this study, we will study the details of the CV-induced CME from chloroplast envelope membranes and revealed a pathway that CCVs influence plant response to ABA signaling and drought, possibly through facilitating the degradation of cytosolic protein GAPC. This study will identify a previously-unknown CME from chloroplast, build a new connection between chloroplast and endomembrane system, and discover a new way that chloroplast influence ABA signaling and drought tolerance. Besides, this study also provides a new idea for genetic improvement of crop tolerance to drought.

网格蛋白介导的胞吞作用和囊泡运输途径参与不同细胞器之间的物质运输和信号传递，也参与调控ABA信号通路。叶绿体膜上是否存在胞吞作用，目前还不清楚。前期我们鉴定了一个诱导叶绿体囊泡化的基因CV，该基因受胁迫诱导表达，编码蛋白定位叶绿体并诱导其形成囊泡，是一条叶绿体降解的新途径。但是，CV诱导囊泡形成的分子机制还不清。我们近期的研究结果表明CV与网格蛋白重链CHC2相互作用，通过网格蛋白介导的胞吞作用来诱导叶绿体被膜形成囊泡。本项目以CV-CHC2相互作用为线索，在模式植物拟南芥中深入解析CV诱导叶绿体被膜发生胞吞作用的分子机制，同时阐述CV诱导的囊泡可以促进细胞质蛋白GAPC的降解从而影响ABA信号途径和干旱胁迫应答的具体过程。本研究不仅可以揭示一条来自叶绿体被膜的新的胞吞途径，完善植物细胞内囊泡运输的调控网络，而且为研究叶绿体与胞质互作提供新的线索，并为农作物的抗旱性改良提供新的思路。

网格蛋白介导的胞吞作用和囊泡运输途径参与植物细胞中不同细胞器之间的物质运输和信号传递，同时也通过调控ABA信号参与植物干旱胁迫的应答。胞吞囊泡只在植物细胞的质膜和高尔基体上产生，叶绿体膜上是否产生胞吞囊泡，目前还不清楚。本项目的研究结果表明：一个诱导叶绿体囊泡化的蛋白CV与网格蛋白重链CHC2相互作用，通过网格蛋白介导的胞吞作用来诱导叶绿体内被膜形成囊泡，同时发现CV诱导的囊泡可以通过促进细胞质蛋白GAPC的降解来影响ABA信号途径和干旱胁迫应答。本研究不仅可以揭示了一条来自叶绿体被膜的新的胞吞途径，进一步完善了植物细胞内囊泡运输的调控网络，而且为研究叶绿体与胞质互作提供新的线索，并为农作物的抗旱性改良提供新的思路。项目取得主要结果和进展如下：1）编码网格蛋白重链CHC2和负责囊泡切割的激动蛋白DRP1A基因的缺失突变会抑制CV诱导的叶绿体囊泡化及叶绿体的降解和叶片衰老；2）CV定位叶绿体内被膜并诱导其形成囊泡；3）CV与GAPC互作并加速其降解；4）沉默CV基因可以提高GAPC蛋白的丰度，从而提高对ABA的敏感性及干旱胁迫的抗性；5）CV基因可以通过逆向信号来提高植物的抗逆性；6）基因编辑敲除水稻OsCV基因可以显著提高水稻的抗旱性。在本项目的资助下，本人以通讯作者发表SCI论文3篇（全是第一标注），其中中科院一区论文2篇（Cell Reports和Plant Journal各一篇），两篇论文皆被多家学术媒体报道；同时发表国内核心期刊一篇，该论文获得第六届《植物生理学报》奖。资助培养博士3人，硕士1人。总体而言，项目资金使用合理，进展良好，成果突出，具有一定的应用前景。

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