Cuticular wax biosynthesis, regulation and intracellular trafficking

角质层是一种细胞外结构，覆盖着陆地植物的主要空气器官，作为防止水分流失、紫外线、病原体和昆虫的保护屏障。它由角质层基质组成，角质层基质被角质层蜡覆盖和渗透。蜡的主要成分来源于饱和甚长链脂肪酸（VLCFAs，长度为>C20），通过两种生物合成途径：醇生成途径和烷烃生成途径。不同物种中脂肪族蜡的组成相似，表明蜡的生物合成在植物中具有高度保守性。******我们已经成功地利用模式植物拟南芥的缺蜡突变体来鉴定和研究与蜡沉积有关的基因。然而，我们对几个关键领域的理解仍然有限，包括VLCFA蜡前体的伸长和蜡链长度的功能意义，蜡生物合成的调节，以及蜡在表皮细胞到植物表面的细胞内运输。在这项拨款申请中，我提出以下目标，以解决我们在知识方面的这些不足：(1)研究植物进化过程中蜡特异性延伸机制的获得，以及蜡链长度对角质层结构和植物抗逆性的功能意义；(2)确定泛素依赖蛋白降解在蜡生物合成调控中的作用；(3)确定蜡在植物表皮中如何从内质网转运到质膜。******本研究将促进我们对表皮蜡的生物合成、其生理重要性、蜡沉积和蜡分泌的调节的理解。这一信息对于角质层基因工程提高作物抗旱能力以及对病虫害的抗性至关重要。此外，蜡生物合成的知识具有工业应用，因为蜡具有独特的物理性质，使其成为各种产品（例如化妆品，食品添加剂，工业润滑剂）和可再生高效生物燃料生产的有用底物。

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.