Polar Lipid Trafficking Between the Endoplasmic Reticulum and the Chloroplast

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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.