Li Fengling, Wu Xuemin, Lam Patricia, Bird David, Zheng Huanquan, Samuels Lacey, Jetter Reinhard, Kunst Ljerka
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
Plant Physiol. 2008 Sep;148(1):97-107. doi: 10.1104/pp.108.123471. Epub 2008 Jul 11.
Wax esters are neutral lipids composed of aliphatic alcohols and acids, with both moieties usually long-chain (C(16) and C(18)) or very-long-chain (C(20) and longer) carbon structures. They have diverse biological functions in bacteria, insects, mammals, and terrestrial plants and are also important substrates for a variety of industrial applications. In plants, wax esters are mostly found in the cuticles coating the primary shoot surfaces, but they also accumulate to high concentrations in the seed oils of a few plant species, including jojoba (Simmondsia chinensis), a desert shrub that is the major commercial source of these compounds. Here, we report the identification and characterization of WSD1, a member of the bifunctional wax ester synthase/diacylglycerol acyltransferase gene family, which plays a key role in wax ester synthesis in Arabidopsis (Arabidopsis thaliana) stems, as first evidenced by severely reduced wax ester levels of in the stem wax of wsd1 mutants. In vitro assays using protein extracts from Escherichia coli expressing WSD1 showed that this enzyme has a high level of wax synthase activity and approximately 10-fold lower level of diacylglycerol acyltransferase activity. Expression of the WSD1 gene in Saccharomyces cerevisiae resulted in the accumulation of wax esters, but not triacylglycerol, indicating that WSD1 predominantly functions as a wax synthase. Analyses of WSD1 expression revealed that this gene is transcribed in flowers, top parts of stems, and leaves. Fully functional yellow fluorescent protein-tagged WSD1 protein was localized to the endoplasmic reticulum, demonstrating that biosynthesis of wax esters, the final products of the alcohol-forming pathway, occurs in this subcellular compartment.
蜡酯是由脂肪醇和脂肪酸组成的中性脂质，其两个部分通常具有长链（C(16)和C(18)）或极长链（C(20)及更长）的碳结构。它们在细菌、昆虫、哺乳动物和陆生植物中具有多种生物学功能，也是各种工业应用的重要底物。在植物中，蜡酯主要存在于覆盖初生茎表面的角质层中，但在少数植物物种的种子油中也会大量积累，包括沙漠灌木霍霍巴（西蒙得木），它是这些化合物的主要商业来源。在此，我们报告了双功能蜡酯合酶/二酰基甘油酰基转移酶基因家族成员WSD1的鉴定和特征，它在拟南芥茎的蜡酯合成中起关键作用，这首先通过wsd1突变体茎蜡中蜡酯水平的严重降低得到证明。使用表达WSD1的大肠杆菌蛋白提取物进行的体外测定表明，该酶具有高水平的蜡合酶活性和大约低10倍的二酰基甘油酰基转移酶活性。WSD1基因在酿酒酵母中的表达导致蜡酯而非三酰甘油的积累，表明WSD1主要作为蜡合酶发挥作用。对WSD1表达的分析表明，该基因在花、茎顶端和叶中转录。带有黄色荧光蛋白标签的完全功能性WSD1蛋白定位于内质网，这表明蜡酯（醇形成途径的最终产物）的生物合成发生在这个亚细胞区室中。
