Cuticular wax biosynthesis, regulation and intracellular trafficking

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The cuticle is an extracellular structure that coats the primary aerial organs of land plants and serves as a protective barrier against water loss, UV light, pathogens and insects. It is composed of a cutin matrix that is covered and infiltrated by cuticular wax. Major wax components are derived from saturated very long chain fatty acids (VLCFAs; >C20 in length) via two biosynthetic pathways: an alcohol-forming and an alkane-forming pathway. Similar composition of aliphatic wax constituents in diverse species suggests that wax biosynthesis is highly conserved in plants. We have successfully used wax-deficient mutants of the model plant Arabidopsis thaliana to identify and study genes involved in wax deposition. However, our understanding in several key areas remains limited, including the elongation of VLCFA wax precursors and the functional significance of wax chain length, the regulation of wax biosynthesis, and the intracellular traffic of waxes in epidermal cells en route to the plant surface. In this grant application, I propose the following objectives to address these deficiencies in our knowledge: (1) investigate the acquisition of wax-specific elongation machinery during plant evolution, and the functional significance of wax chain length for cuticle structure and plant stress tolerance, (2) establish the role of ubiquitin-dependent protein degradation in the regulation of wax biosynthesis, and (3) determine how wax is transported from the endoplasmic reticulum to the plasma membrane in the plant epidermis.The proposed research will advance our understanding of cuticular wax biosynthesis, its physiological importance, the regulation of wax deposition, and wax secretion. This information is essential for genetic engineering of cuticles to improve crop tolerance to drought, as well as resistance to pathogens and insects. Additionally, knowledge of wax biosynthesis has industrial applications because waxes possess unique physical properties that make them useful substrates for a wide range of products (e.g. cosmetics, food additives, industrial lubricants), and production of renewable high-efficiency biofuels.