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UBC Theses and Dissertations

The mechanism for fatty acids trafficking from plastids to the endoplasmic reticulum Liu, Mingzhe


Fatty acids (FAs) are building blocks for different glycerolipids, including phospholipids and galactolipids that serve as major structural components of cell membranes, as well as triacylglycerols (TAGs), which are the main form of energy and carbon storage in plants. They are also precursors of the plant surface lipids: cutin, cuticular waxes, and suberin, which play roles during the plant’s resistance to drought, pathogens, or insects. In-plant cells, de novo fatty acid synthesis happens exclusively within plastids with the growing fatty acyl chain attached to the acyl carrier protein (ACP). Once completed, the majority of these fatty acids are removed from ACP by thioesterases and re-attached to coenzyme A (CoA) under the activities of long-chain acyl-CoA synthetase (LACS) to make membrane lipids, storage or surface lipids in the ER, the major site for lipid assembly. Since the production of fatty acids and the production of complex lipids happen in different organelles, a transport system between plastids and other subcellular compartments is required in order to deliver FAs from the plastid to the ER. In Arabidopsis, neither the lacs9 single knock-out mutants which removed all plastidial LACS activities, nor the lacs4 single mutants which removed the activity of an ER LACS showed any visible phenotype while the lacs4lacs9 double mutants are dwarf, and with decreased seed oil and stem wax content. These not only suggest the functional overlap between the plastidial-LACS9 and ER-LACS4 but also suggest proposed access for the ER-LACS to the fatty acids from the plastid envelopes. In my research, I have proved such access directly by re-targeting the plastidial-LACS9 to the ER and complemented the dwarf, seed oil, and stem wax content phenotypes of the lacs4lacs9 double mutants. Besides, I also showed that the outer-envelope LACS9 and inner-envelope FAX1 could form a complex, which play roles during fatty acid export from the plastid, while the ER-LACS4 is not associate with FAX1 even it is functionally equivalent with LACS9 in such pathway.

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