College of Life Science, Shanxi University, Taiyuan, 030006, China; Shanxi Key Laboratory for Research and Development of Regional Plants, Taiyuan, 030006, China.
Taiyuan University of Technology, Taiyuan, 030024, China.
Plant Physiol Biochem. 2019 Jun;139:325-332. doi: 10.1016/j.plaphy.2019.03.032. Epub 2019 Mar 28.
Cysteine is the first organic molecule generated during the assimilation of sulfate. As such, cysteine and its derivatives are always essential signal molecules and thus have important roles in the regulation of many plant processes. O-acetylserine (thiol) lyase (OASTL) catalyzes the last step of the biosynthesis of cysteine. At present, detailed and comprehensive work about these enzymes has only been reported from the plant Arabidopsis thaliana, though sporadic studies on OASTL have been conducted on other dicots, such as spinach and soybean. However, few reports on the functions of OASTLs in monocots have been found in the literature. Here in this study, we obtained four SiOASTL genes (SiOASTL7, SiOASTL8, SiOASTL9 and SiOASTL10) from foxtail millet and analyzed their potential functions. Phylogenetically, the four SiOASTL genes did not belong to any published subfamily of the OASTL genes; instead they constituted a new subfamily specific to the OASTL genes from monocots. In sequencing, we found that with the exception of the pseudogene SiOASTL8, proteins encoded by the other three genes exhibited high similarity with OASTL proteins from Arabidopsis, though the critical PLP-binding sites of both SiOASTL7 and SiOASTL10 were missing. The enzymatic activity assays demonstrated that SiOASTL9 has the ability to catalyze the biosynthesis of both cysteine and S-sulfocysteine, while SiOASTL7 and SiOASTL10 did not possess any previously reported catalyzing abilities. In addition, the gene expression pattern analysis showed that all four genes were widely expressed in various tissues of foxtail millet, and all had a preference in the leaves. Under abiotic stresses, the expression of these genes could be induced by salt and drought stress. Our finding that cadmium could only up-regulate the transcription of SlOASTL8 and SlOASTL9, further indicates the diversified responses of SiOASTLs to abiotic stresses.
半胱氨酸是硫酸盐同化过程中生成的第一个有机分子。因此，半胱氨酸及其衍生物始终是重要的信号分子，因此在许多植物过程的调节中具有重要作用。O-乙酰丝氨酸（硫醇）裂解酶（OASTL）催化半胱氨酸生物合成的最后一步。目前，这些酶的详细和全面的工作仅在植物拟南芥中得到报道，尽管对其他双子叶植物如菠菜和大豆进行了零星的 OASTL 研究。然而，在文献中很少发现有关单子叶植物 OASTL 功能的报道。在本研究中，我们从小麦中获得了四个 SiOASTL 基因（SiOASTL7、SiOASTL8、SiOASTL9 和 SiOASTL10），并分析了它们的潜在功能。系统进化分析表明，这四个 SiOASTL 基因不属于已发表的 OASTL 基因的任何亚家族，而是构成了一个新的、特定于单子叶植物 OASTL 基因的亚家族。在测序过程中，我们发现除了假基因 SiOASTL8 外，其他三个基因编码的蛋白质与拟南芥的 OASTL 蛋白高度相似，尽管 SiOASTL7 和 SiOASTL10 的关键 PLP 结合位点缺失。酶活性测定表明，SiOASTL9 具有催化半胱氨酸和 S-磺基半胱氨酸生物合成的能力，而 SiOASTL7 和 SiOASTL10 则不具有任何先前报道的催化能力。此外，基因表达模式分析表明，这四个基因在谷子的各种组织中广泛表达，并且都偏爱叶片。在非生物胁迫下，这些基因的表达可被盐和干旱胁迫诱导。我们发现镉只能上调 SlOASTL8 和 SlOASTL9 的转录，这进一步表明 SiOASTLs 对非生物胁迫的多样化反应。
