Zhao Na, Zhang Yuan, Li Qiuqi, Li Rufang, Xia Xinli, Qin Xiaowei, Guo Huihong
College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China.
State Key Laboratory of Integrated Pest Management, Institute of Zoology, Chinese Academy of Sciences, 100101, China.
Plant Physiol Biochem. 2015 Feb;87:9-16. doi: 10.1016/j.plaphy.2014.12.009. Epub 2014 Dec 13.
Xanthoceras sorbifolia Bunge is an oilseed tree that grows well on barren lands in dry climate. Its seeds contain a large amount of oil rich in oleic acid (18:1(Δ9)) and linoleic acid (18:2(Δ9, 12)). However, the molecular regulation of oil biosynthesis in X. sorbifolia seeds is poorly understood. Stearoyl-ACP desaturase (SAD, EC 1.14.99.6) is a plastid-localized soluble desaturase that catalyzes the conversion of stearic acid (18:0) to oleic acid, which plays a key role in determining the ratio of saturated to unsaturated fatty acids. In this study, a full-length cDNA of XsSAD was isolated from developing X. sorbifolia embryos. The XsSAD open reading frame had 1194-bp, encoding a polypeptide of 397 amino acids. XsSAD expression in Escherichia coli cells resulted in increased 18:1(Δ9) level, confirming the biological activity of the enzyme encoded by XsSAD. XsSAD expression in Arabidopsis ssi2 mutants partially restored the morphological phenotype and effectively increased the 18:1(Δ9) level. The levels of other unsaturated fatty acids synthesized with 18:1(Δ9) as the substrate also increased to some degree. XsSAD in X. sorbifolia had a much higher expression in embryos than in leaves and petals. XsSAD expression also correlated well with the oleic acid, unsaturated fatty acid, and total fatty acid levels in developing embryos. These data suggested that XsSAD determined the synthesis of oleic acid and contributed to the accumulation of unsaturated fatty acid and total oil in X. sorbifolia seeds. A preliminary tobacco rattle virus-based virus-induced gene silencing system established in X. sorbifolia can also be helpful for further analyzing the functions of XsSAD and other oil synthesis-related genes in woody plants.
文冠果是一种油料树种，在干旱气候下的贫瘠土地上生长良好。其种子含有大量富含油酸（18:1(Δ9)）和亚油酸（18:2(Δ9, 12)）的油脂。然而，文冠果种子中油脂生物合成的分子调控机制尚不清楚。硬脂酰-ACP去饱和酶（SAD，EC 1.14.99.6）是一种定位于质体的可溶性去饱和酶，催化硬脂酸（18:0）转化为油酸，在决定饱和脂肪酸与不饱和脂肪酸比例方面起关键作用。在本研究中，从发育中的文冠果胚中分离出XsSAD的全长cDNA。XsSAD开放阅读框有1194个碱基对，编码一个由397个氨基酸组成的多肽。XsSAD在大肠杆菌细胞中的表达导致18:1(Δ9)水平升高，证实了XsSAD编码酶的生物学活性。XsSAD在拟南芥ssi2突变体中的表达部分恢复了形态表型，并有效提高了18:1(Δ9)水平。以18:1(Δ9)为底物合成的其他不饱和脂肪酸水平也有一定程度的提高。文冠果中的XsSAD在胚中的表达远高于叶和花瓣。XsSAD的表达也与发育中胚中的油酸、不饱和脂肪酸和总脂肪酸水平密切相关。这些数据表明，XsSAD决定了油酸的合成，并有助于文冠果种子中不饱和脂肪酸和总油脂的积累。在文冠果中建立的基于烟草脆裂病毒的病毒诱导基因沉默初步体系，也有助于进一步分析XsSAD和其他与油脂合成相关基因在木本植物中的功能。
