DRPs 蛋白介导拟南芥叶绿体膜重构的机制

Dynamins form a superfamily of large mechanochemical GTPases that include the classical dynamins and dynamin-related proteins (DRPs)。 These GTPase protiens implicated in membrane remodeling, have critical roles in endocytic membrane fission events, fusion and fission of mitochondria, vesicle trafficking and other organelle division events in eukaryotes. Chloroplasts replicate through binary fission to maintain appropriate chloroplast-population density during cell division and expansion, which is an important cellular process in plants. A plant-specific dynamin-related protein DRP5B is identified in Arabidopsis, playing an important role in chloroplast division. Mutants of DRP5B exhibit defects in chloroplast constriction, and have enlarged, dumbbell-shaped chloroplasts. A GFP-DRP5B fusion protein localizes to a ring at the chloroplast division site throughout dividing process. These data suggest that DRP5B probably is a key factor to mediate chloroplast membrane fission at the division site. However, it is unknown whether DRP5B has ability to fragment membrane and how it remodels chloroplast envelope membrane at the division site. In addition, FZL protein is another plant-specific member of the dynamin superfamily. It is targeted to chloroplast inner envelope membrane and thylakoid. fzl knockout mutants exhibits abnormal morphologies of chloroplast and thylakoid, indicating that FZL might function in thylakoid formation. But GTPase activity of FZL is unknown. Here in our project, we will use diverse strategies to analyze the function of DRP5B and FZL on chloroplast-associated membrane-remodeling process, to understand the underlying mechanism of chloroplast division and thylakoid formation in plants.

Dynamin和DRP是一类机械化学偶联的GTPases。它们介导在胞吞作用、膜泡运输、细胞器分裂等生物学过程中的生物膜重构- - 即膜的断裂与融合。叶绿体是植物进行能量合成的特有细胞器，其遗传的稳定性和形态建成对植物的生长发育有着重要作用。研究发现，叶绿体分裂是由一个在叶绿体中部装配的蛋白复合物驱动被膜向内缢缩，最后断裂而完成的。植物中发现一种具有GTPase活性的DRP5B蛋白。在其功能缺失的突变体中，叶绿体分裂停滞在最后阶段，暗示该DRP蛋白可能介导叶绿体分裂过程中被膜的重构，然而缺乏相关证据。此外，在植物中还有一种DRP同源蛋白-FZL影响叶绿体及其内膜系统的形态建成。但是该蛋白是否具有GTPase活性，以及如何影响叶绿体内膜系统的形态建成的机制不清楚。在本课题中，我们将运用多种手段研究DRP5B和FZL的功能和特性，揭示它们分别在叶绿体分裂过程中介导被膜重构和类囊体形成的分子机制。

叶绿体是植物细胞进行光合作用的场所，细胞内叶绿体数目和体积的相对恒定是植物进行光合作用的前提。 叶绿体是通过细菌类似的均等细胞分裂方式进行增殖的。虽然报道了很多叶绿体分裂相关的蛋白因子，然而叶绿体均等分裂的调控机理和被膜运动的分子机制仍不清楚。本课题中，我们通过细胞学、遗传学和生物化学的实验方法分析了叶绿体分裂复合物在内膜上起始装配的调控机理；叶绿体分裂复合物在分裂位点跨内外被膜的装配方式；和细胞质Dynamin 蛋白招募到叶绿体外膜分裂位点及行使膜断裂融合功能的机理。我们的研究结果表明叶绿体分裂复合物的装配是由叶绿体内膜基质侧FtsZ-ring开始装配的，内膜蛋白ARC6锚定FtsZ-ring在叶绿体中部的聚合受到MCD1、ARC3、MinD和MinE四个分子的协同调控；2. 揭示了叶绿体内外膜上分裂相关蛋白ARC6、PARC6、PDV1 和PDV2的装配连接方式；3.揭示了细胞质Dynamin蛋白DRP5B招募和活性调控的机理。我们的研究成果以申请人为第一作者和通讯作者身份发表在Plant Cell 和 Plant Physiology杂志上，为深入分析叶绿体发育和增殖调控的分子机理奠定了基础。