Divergent evolution of oxidosqualene cyclases in plants
Divergent evolution of oxidosqualene cyclases in plants
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植物中氧化角鲨烯环化酶的趋异进化
DOI：
10.1111/j.1469-8137.2011.03997.x
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发表时间：
2012-03-01
期刊：
影响因子：
9.4
通讯作者：
Qi, Xiaoquan
中科院分区：
文献类型：
--
作者：
Xue, Zheyong;Duan, Lixin;Qi, Xiaoquan
三萜类化合物是植物体内最大的代谢物之一，具有重要的功能。通过类异戊二烯途径，通过2，3-氧化桂烯的酶促环化反应，合成了一系列不同的三萜类骨架。低等植物衣藻和苔藓(Physcomitrella Patens)的基因组中只含有1个氧化苦参烯环化酶(OSC)基因，而高等植物基因组中含有9~16个OSC基因。在这里，我们对水稻OSCs的功能进行了分析，并对拟南芥、水稻、高粱和短柄蕨属植物中的96个OSCs进行了严格的系统发育分析。功能分析鉴定了水稻异甘油醇合成酶(Osias)的一个氨基酸序列(由Os11g35710/OsOSC11编码)。我们的系统发育分析表明，在高等植物中，OSC成员的扩展主要是通过串联复制、正向选择和多样化进化来实现的，并证实了以前的观点，即双子叶三萜合成酶来自于祖先的羊毛甾醇合成酶，而不是直接来自它们的环青蒿醇合成酶。系统发育树与原甾基和达马烯基阳离子的反应机制一致，这两种阳离子孕育了多种三萜类骨架类型，使我们能够预测未鉴定的OSCs的功能。
Triterpenes are one of the largest classes of plant metabolites and have important functions. A diverse array of triterpenoid skeletons are synthesized via the isoprenoid pathway by enzymatic cyclization of 2,3-oxidosqualene. The genomes of the lower plants Chlamydomonas reinhardtii and moss (Physcomitrella patens) contain just one oxidosqualene cyclase (OSC) gene (for sterol biosynthesis), whereas the genomes of higher plants contain nine to 16 OSC genes. Here we carry out functional analysis of rice OSCs and rigorous phylogenetic analysis of 96 OSCs from higher plants, including Arabidopsis thaliana, Oryza sativa, Sorghum bicolor and Brachypodium distachyon. The functional analysis identified an amino acid sequence for isoarborinol synthase (OsIAS) (encoded by Os11g35710/OsOSC11) in rice. Our phylogenetic analysis suggests that expansion of OSC members in higher plants has occurred mainly through tandem duplication followed by positive selection and diversifying evolution, and consolidated the previous suggestion that dicot triterpene synthases have been derived from an ancestral lanosterol synthase instead of directly from their cycloartenol synthases. The phylogenetic trees are consistent with the reaction mechanisms of the protosteryl and dammarenyl cations which parent a wide variety of triterpene skeletal types, allowing us to predict the functions of the uncharacterized OSCs.