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Plant lipid trafficking : the cell biology of cuticular lipid export and membrane contact sites of Arabidopsis thaliana McFarlane, Heather

Abstract

The plant cuticle coats the primary aerial tissues of all land plants to provide protection against non-­‐stomatal water loss. Though the biosynthesis of cuticular lipids is now relatively well understood, the mechanisms of cuticular lipid export remain unclear. The objective of this thesis was to characterize several transporters required for cuticular lipid export and to determine the route of cuticular lipid export from their site of synthesis inside the cell to their site of accumulation on the cell surface. Based on interaction studies between two ATP-­‐binding cassette transporters (ABCG11 and ABCG12) and the chemical phenotypes of their mutants, a model for the influence of ABC dimerization on subcellular localization and substrate specificity of these transporters is presented in the context of cuticular lipid export (Chapter 2). Analysis of several well-­‐characterized secretory pathway mutants further indicates that at least some cuticular lipids reach these plasma membrane transporters via vesicular trafficking through the Golgi apparatus (Chapter 3). Furthermore, these mutant studies reveal a form and function relationship between the structure of the endoplasmic reticulum (ER) and its biosynthetic capacity, with respect to lipid synthesis (Chapter 3). Finally, ER-­‐plasma membrane contact sites are investigated as a possible second route of cuticular lipid export (Chapter 4). While the frequency of contact sites is not correlated with cuticular lipid export, it remains possible that lipid trafficking may occur at these sites. Isolation and proteomic analysis of these membrane sub-­‐fractions reveals a possible role for ER-­‐plasma membrane contact sites in lipid remodeling or recycling, rather than cuticular lipid export. Taken together, these results build a complete model of cuticular lipid export from the site of synthesis to the site of lipid accumulation.

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