植物中的不饱和脂肪酸由脂肪酸去饱和酶(Fatty acid desaturase, FAD)合成, 它在植物的生长发育以及植物非生物胁迫方面起着重要的作用。文章采用RT-PCR方法, 从水稻日本晴(Oryza sativa L.)中克隆了分别与FAD2、FAD6同源的脂肪酸脱氢酶序列, 命名为OsFAD2和OsFAD6。OsFAD2的ORF为1 167 bp, 推测其编码蛋白含有388个氨基酸, 等电点为8.17, 分子量为52.24 kDa, C端有内质网定位序列; OsFAD6的ORF长度为1 365 bp, 推测编码454个氨基酸的蛋白质序列, 分子量44.35 kDa, 等电点为9.24, 推测N端38个氨基酸为叶绿体导肽。两者都具有膜整合脂肪酸去饱和酶特有的3个组氨酸簇。RT-PCR分析表明, OsFAD2和OsFAD6在水稻所有器官中都表达, 在叶中表达量为最高。在水稻FAD基因家族中, 叶中OsFAD2、OsFAD6 的mRNA对低温不响应, 而OsFAD7和OsFAD8的 mRNA在低温下上升。水稻叶中OsFAD2、OsFAD6、OsFAD3和OsFAD7的mRNA表达具有昼夜节律性, 在光照下表达量低, 而在随后的黑暗中表达量高, OsFAD6和OsFAD7 mRNA表达的昼夜节律性可能与水稻幼苗叶片中NADPH量的改变有关。
Unsaturated fatty acids are synthesized by fatty acid desaturase in plant, which play an important role in plant development and defense to abiotic stresses. The key enzymes for the conversion of oleic into linoleic acid were isolated from rice (Oryza sativa L.) and were designated OsFAD2 and OsFAD6, respectively. The open reading frame (ORF) of OsFAD2 was 1 167 bp in length, which encoded a 388 amino acids sequence with the isoelectric point of 8.17 and molecular mass of 52.24 kDa, the OsFAD2 protein contained a C-terminal ER retrieval motif. The ORF of OsFAD6 was 1 365 bp in length and the predicted OsFAD6 protein has 454 amino acids with an estimated molecular mass of 44.35 kDa and an isoelectric point of 9.24, the predicted OsFAD6 protein possessed a putative N-terminal plastidial signal peptide. Both of them had three his-boxes, which were peculiar to membrane integrated fatty acid desaturase by Clustal X analysis. RT-PCR analysis showed that both genes were expressed in all tissues rice seedlings, with the maximum transcript accumulation in leaves. Among FAD family members of Oryza sativa L., the mRNA abundance of OsFAD2 and OsFAD6 in leaves did not change under cold stress; however, the mRNA abundance of OsFAD7 and OsFAD8 increased in the same condition. It was also found that the expression of FAD family members had diurnal rhythm phenomena. Based on the results of this study, it suggested that diurnal rhythm expression of OsFAD6 and OsFAD7 was related to the change of NADPH abundance.
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