Cuticular wax biosynthesis, regulation and intracellular trafficking

角质层是一种细胞外结构，覆盖在陆地植物的初级气生器官上，是防止水分流失、紫外线、病原体和昆虫的保护性屏障。它是由角质基质组成的，角质基质被角质蜡覆盖和渗透。蜡的主要成分来自饱和的超长链脂肪酸(VLCFAs；&GT；C20)，通过两条生物合成途径：醇形成途径和烷烃形成途径。不同物种脂肪蜡组分的相似组成表明，蜡的生物合成在植物中高度保守。*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，我们在几个关键领域的了解仍然有限，包括VLCFA蜡前体的延长和蜡链长度的功能意义，蜡质生物合成的调节，以及蜡质在到达植物表面的过程中在表皮细胞中的细胞内运输。在这项赠款申请中，我提出了以下目标来解决我们知识中的这些不足：(1)调查植物进化过程中蜡专化延伸机制的获得，以及蜡链长度对角质层结构和植物抗逆性的功能意义，(2)建立泛素依赖的蛋白质降解在调节蜡生物合成中的作用，以及(3)确定蜡如何从植物表皮的内质网运输到质膜。*建议的研究将促进我们对角质层蜡的生物合成、其生理重要性、蜡沉积的调节和蜡的分泌的理解。这些信息对于利用角质层进行基因工程以提高作物对干旱的耐受性以及对病原体和昆虫的抵抗力至关重要。此外，蜡的生物合成知识具有工业应用，因为蜡具有独特的物理性质，使其成为广泛产品(如化妆品、食品添加剂、工业润滑油)的有用底物，并生产可再生的高效生物燃料。

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.