Abstract

Nervonic acid (24:1) is a major component in nerve and brain tissues and it has important applications in food and pharmaceutical industries. Malania oleifera seeds contain about 40% nervonic acid. However, the mechanism of nervonic acid biosynthesis and accumulation in seeds of this endangered tree species remains unknown. In this study, developmental changes in fatty acid composition within embryos and their pericarps were investigated. Nervonic acid proportions steadily increased in developing embryos but 24:1 was not detected in pericarps at any stage. Two 3-ketoacyl-CoA synthase (KCS) homologs have been isolated from M. oleifera developing seeds by homologous cloning methods. Both KCSs are expressed in developing embryos but not detected in pericarps. Based on a phylogenetic analysis, these two KCSs were named as MoKCS4 and MoKCS11. Seed-specific expression of the MoKCS11 in Arabidopsis thaliana led to about 5% nervonic acid accumulation, while expression of the MoKCS4 did not show an obvious change in fatty acid composition. It is noteworthy that the transformation of the same MoKCS11 construct into two Brassica napus cultivars with high erucic acid did not produce the expected accumulation of nervonic acid, although expression of MoKCS11 was detected in the developing embryos of transgenic lines. In contrast, overexpression of MoKCS11 results in similar level of nervonic acid accumulation in camelina, a species which contains a similar level of 11Z-eicosenoic acid as does Arabidopsis thaliana. Taken together, the MoKCS11 may have a substrate preference for 11Z-eicosenoic acid, but not for erucic acid, in planta.

中文翻译：

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来自Malania oleifera的3-酮酰基-CoA合酶11（KCS11）同源物在富含11Z-二十碳烯酸的植物中合成神经酸

摘要

神经酸（24：1）是神经和脑组织的主要成分，在食品和制药行业中具有重要的应用。疟原虫种子含有约40％的神经酸。然而，这种濒危树种的种子中神经酸生物合成和在种子中积累的机制仍然未知。在这项研究中，研究了胚胎及其果皮中脂肪酸组成的发育变化。神经酸比例在发育中的胚胎中稳定增加，但在任何阶段果皮中均未检测到24：1。已经通过同源克隆方法从油果分枝杆菌发育的种子中分离了两个3-酮酰基-CoA合酶（KCS）同源物。两个KCS在发育中的胚胎中表达，但在果皮中未检测到。根据系统发育分析，这两个KCS分别命名为MoKCS4和MoKCS11。MoKCS11在拟南芥中的种子特异性表达导致约5％的神经酸积累，而MoKCS4的表达在脂肪酸组成上没有显示出明显的变化。值得注意的是，尽管在转基因品系的发育胚中检测到MoKCS11的表达，但将相同的MoKCS11构建体转化为具有高芥酸的两个甘蓝型油菜品种并没有产生预期的神经酸积累。相反，MoKCS11的过表达导致在山茶中的神经酸积累水平相似，山茶中的11Z-二十碳烯酸含量与拟南芥中相似。两者合计，在植物中，MoKCS11可能对11Z-二十碳烯酸具有底物偏好，但对芥酸没有底物偏好。