Department of Bioenergy Science and Technology, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Republic of Korea.
Plant Physiol. 2013 Jun;162(2):567-80. doi: 10.1104/pp.112.210450. Epub 2013 Apr 12.
Very-long-chain fatty acids (VLCFAs) with chain lengths from 20 to 34 carbons are involved in diverse biological functions such as membrane constituents, a surface barrier, and seed storage compounds. The first step in VLCFA biosynthesis is the condensation of two carbons to an acyl-coenzyme A, which is catalyzed by 3-ketoacyl-coenzyme A synthase (KCS). In this study, amino acid sequence homology and the messenger RNA expression patterns of 21 Arabidopsis (Arabidopsis thaliana) KCSs were compared. The in planta role of the KCS9 gene, showing higher expression in stem epidermal peels than in stems, was further investigated. The KCS9 gene was ubiquitously expressed in various organs and tissues, including roots, leaves, and stems, including epidermis, silique walls, sepals, the upper portion of the styles, and seed coats, but not in developing embryos. The fluorescent signals of the KCS9::enhanced yellow fluorescent protein construct were merged with those of BrFAD2::monomeric red fluorescent protein, which is an endoplasmic reticulum marker in tobacco (Nicotiana benthamiana) epidermal cells. The kcs9 knockout mutants exhibited a significant reduction in C24 VLCFAs but an accumulation of C20 and C22 VLCFAs in the analysis of membrane and surface lipids. The mutant phenotypes were rescued by the expression of KCS9 under the control of the cauliflower mosaic virus 35S promoter. Taken together, these data demonstrate that KCS9 is involved in the elongation of C22 to C24 fatty acids, which are essential precursors for the biosynthesis of cuticular waxes, aliphatic suberins, and membrane lipids, including sphingolipids and phospholipids. Finally, possible roles of unidentified KCSs are discussed by combining genetic study results and gene expression data from multiple Arabidopsis KCSs.
非常长链脂肪酸（VLCFAs）的链长从 20 到 34 个碳原子，参与了各种生物学功能，如膜成分、表面屏障和种子储存化合物。VLCFA 生物合成的第一步是两个碳原子缩合到酰基辅酶 A，这是由 3-酮酰基辅酶 A 合酶（KCS）催化的。在这项研究中，比较了 21 个拟南芥（Arabidopsis thaliana）KCS 的氨基酸序列同源性和信使 RNA 表达模式。进一步研究了 KCS9 基因在茎表皮剥片中表达高于茎中的作用。KCS9 基因在各种器官和组织中广泛表达，包括根、叶和茎，包括表皮、蒴果壁、萼片、花柱的上部和种皮，但在发育中的胚胎中不表达。KCS9::增强黄色荧光蛋白构建体的荧光信号与 BrFAD2::单体红色荧光蛋白的信号融合，后者是烟草（Nicotiana benthamiana）表皮细胞内质网标记物。在膜和表面脂质分析中，kcs9 敲除突变体中 C24 VLCFAs 的含量显著降低，而 C20 和 C22 VLCFAs 的含量增加。在 Cauliflower mosaic virus 35S 启动子控制下表达 KCS9 可挽救突变体表型。综上所述，这些数据表明 KCS9 参与了 C22 到 C24 脂肪酸的延长，这是角质层蜡、脂肪性愈创木酚和膜脂（包括神经酰胺和磷脂）生物合成的必需前体。最后，通过结合多个拟南芥 KCS 的遗传研究结果和基因表达数据，讨论了未鉴定 KCS 的可能作用。
