Polar Lipid Trafficking Between the Endoplasmic Reticulum and the Chloroplast

细胞和胞内室(细胞器)被生物膜包围。极性脂是细胞膜的组成部分，不同膜之间的脂转移对所有细胞的生长和维持都是必不可少的。随着拟南芥中极性脂类从内质网(ER)向叶绿体光合膜转运功能缺陷的新的遗传突变体的分离，鉴定出了与细菌ABC转运蛋白的渗透酶(TGD1)、底物结合蛋白(TGD2)和三磷酸腺苷结合蛋白(TDG3)具有惊人相似性的三种蛋白(TGD1-3)。推测TGD1-3蛋白是叶绿体被膜中磷脂酸(PA)转运体的组成部分。功能的丧失会导致PA的蓄积和内质网衍生的甘油三脂转化为三酰甘油。此外，在突变体中，叶绿体外层的半乳糖基转移酶被激活，导致低聚半乳糖脂的积累。本项目的重点是三个TGD蛋白的功能分析及其在叶绿体被膜脂类传递中的作用。具体目的是(1)确定TGD1-3蛋白的亚细胞定位，(2)确定TGD1、TGD2和TGD3之间的物理相互作用，(3)确定所提议的复合体的脂质底物，以及(4)确定TGD3的ATPase活性。该项目涉及博士后研究人员、研究生和本科生的参与，并为不同技能水平的人提供培训机会。由于所采用的方法从拟南芥遗传学到植物生物化学和植物细胞生物学，因此为所有受训者提供了广泛的培训经验。此外，博士后研究人员将在学生指导方面获得宝贵经验。

Cells and intracellular compartments (organelles) are enclosed by biological membranes. Polar lipids are the building blocks of cell membranes and lipid transfer between different membranes is essential for the growth and maintenance of all cells. The isolation of new genetic mutants of Arabidopsis with deficiencies in the transfer of polar lipids from the endoplasmic reticulum (ER) to the photosynthetic membranes in chloroplasts has led to the identification of three proteins (TGD1-3) with striking similarity to the permease- (TGD1), substrate-binding- (TGD2), and ATP-binding proteins (TDG3) of predicted bacterial ABC transporters. It is hypothesized that the TGD1-3 proteins are components of a phosphatidic acid (PA) translocator in the chloroplast envelopes. Loss of function leads to the accumulation of PA and the diversion of ER-derived glycerolipids into triacylglycerols. In addition, a processive galactosyltransferase at the outer chloroplast envelope is activated in the mutants, which causes the accumulation of oligogalactolipids. This project focuses on the functional analysis of the three TGD proteins and their role in lipid transfer at the chloroplast envelopes. Specific aims are to (1) determine the subcellular localization of the TGD1-3 proteins, (2) determine the physical interaction between TGD1, TGD2 and TGD3, (3) determine the lipid substrate for the proposed complex and (4) determine the ATPase activity for TGD3. The project involves the participation of postdoctoral researchers, graduate students as well as undergraduate students and offers training opportunities for persons with different skill levels. Because the employed approaches are ranging from Arabidopsis genetics, to plant biochemistry and plant cell biology, a broad training experience is provided to all trainees. In addition, postdoctoral researchers will gain valuable experience in the supervision of students.