自噬在拟南芥根尖细胞降解液泡生成中的作用机制

The vacuole not only is essential for cellular homeostasis, but also participates in regulating plant growth and stress adaptation. In the root tip, biogenesis of the lytic vacuole takes place along with the transition from cell division to cell differentiation, until the cell volume is filled up with the central vacuole. Four organelles are known as resources for lytic vacuole (LV) biogenesis: the Endoplasmic Reticulum, the Trans Golgi Network, the Protein Storage Vacuole, and the Autophagosome. Among them, the function of the autophagosome in LV biogenesis has been the least studied. We observed that in the root tip of the Arabidopsis seedling, autophagosomes accumulate in the transition zone, coinciding with LV biogenesis. The autophagy deficient mutants atg5 and atg7 have short primary roots, and their root phenotypes become more severe upon salt stress. Meanwhile, their vacuoles fail to accumulate Na+. In contrast, over-expression of ATG8 confers salt tolerance to the transgenic seedlings, and they accumulate more Na+ in the vacuole. We hypothesized that the contribution of autophagosome to the lytic vacuole could be highly dynamic, and that it might serve as a major pathway in LV biogenesis under stress conditions. We plan to elucidate the mechanism in which autophagy contribute to the formation of the lytic vacuole, to identify the key regulators in the process, and to find out whether the process is salt inducible. The outcomes may facilitate our understanding of the fundamental question on how vacuoles form in planta, and may serve as a new theory for breeding salt tolerant crops.

液泡不仅对植物细胞的稳态维持至关重要，也参与调控植物的生长与抗逆。 在幼苗根尖中，随着新生细胞从分裂转向分化，降解液泡也从无到有，从小到大，直到占据细胞的大部分体积。研究表明降解液泡有四个来源：内质网、反面高尔基体管网状结构、蛋白贮存液泡和自噬体。其中，自噬体在降解液泡生成中的机制研究最少。我们观察到，在拟南芥幼苗根尖中，自噬体大量出现在转换区，与降解液泡的建成同步。自噬缺失突变体atg5、atg7主根短于野生型，在盐胁迫下根的表型加强，并且液泡不能正常积累钠离子。过表达ATG8则使液泡积累更多的钠离子,更加耐盐。推测自噬对降解液泡的贡献高度动态化，是在逆境条件下支持液泡生成的重要途径。本项目拟研究自噬在根尖细胞降解液泡生成中的作用机制，找到该过程的关键调控子，并探明该过程是否受到盐胁迫诱导。研究结果有助于我们回答液泡如何生成这一基本问题，也可为抗盐作物培育提供新的理论依据。

盐胁迫是造成全球作物减产的主要原因之一。面对盐胁迫，植物往往下调光合作用，减缓生长；同时迅速合成渗透调节物质、抗逆相关蛋白，切入抗逆模式。我们前期发现提高自噬流是模式植物拟南芥快速应答盐胁迫的方式之一，自噬体对液泡生成与钠离子区室化的贡献对耐盐性重要。本项目发现磷脂酰肌醇3-磷酸酶MTM是盐胁迫下自噬-液泡通路的重要调控者。盐胁迫调控MTM的转录与蛋白周转；MTM特异性定位于内质网出口，通过与COPII复合体亚基互作，负调控自噬体生成。mtm敲除突变体自噬流显著提高，在盐胁迫下其叶绿体维持健康形态，液泡内钠离子积累显著增加，耐盐性显著高于野生型。我们还对叶绿体选择性自噬在盐胁迫响应中的作用进行了探索，并利用新合成的药物研究了抑制线粒体ATP产生对液泡形态功能的影响。研究结果丰富了细胞自噬机制，并可应用于抗盐育种。