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香气是茶叶的重要品质之一,萜类物质不仅香气好,而且沸点普遍较高,是构成茶叶香气的重要物质基础,决定着茶叶的香气品质,也可作为茶叶香型划分的依据。在植物中,倍半萜、多萜醇等通过胞质中的甲瓦龙酸(MVA)途径合成。HMG-Co A还原酶(HMGR)催化HMG-Co A(3-羟基-3-甲基戊二酸单酰辅酶A)生成甲瓦龙酸,是依赖MVA萜类合成途径的关键限速反应。为了有助于理解茶树萜类合成的分子遗传机制,通过RACE-PCR方法从茶树中克隆了一个编码HMG-Co A还原酶的c DNA全长序列(命名为Cs HMGR1),该序列由1 979 bp组成,包含一个1 722 bp的完整开放阅读框,编码573个氨基酸。其推定的编码蛋白与橡胶树、旱莲木、人参、荔枝、西洋参、丹参、罗汉果及龙眼的同源蛋白具有80%~82%的序列一致性。利用Cs HMGR1和其它物种HMGR同源蛋白的催化区域构建系统发育树,表明其属于真核生物I类HMGR家族。结构分析表明,Cs HMGR1含有两个跨膜区,推测其与其它真核生物同源蛋白类似地定位于内质网上;含有两个HMG-Co A结合位点、两个NADPH结合位点、四个保守的催化活性残基及一个磷酸化位点,说明磷酸化/去磷酸化很可能也是其活性调节的重要方式。表达分析表明,Cs HMGR1在“大叶龙”叶芽、母株叶芽及花芽都有较强的表达。其表达调控及生理活性对茶叶品质可能有重要影响,并在其功能解析的基础上,有可能作为茶叶品质鉴定及育种的一个依据。
Aroma is one of the important qualities of tea. Terpenoids are not only good in aroma, but also have high boiling point. They constitute the important material basis of the aroma of tea and determine the aroma quality of tea. They can also be used as the basis for the classification of tea aroma. In plants, sesquiterpenes, dolichols and the like are synthesized by the mevalonic acid (MVA) pathway in the cytoplasm. HMG-Co A reductase (HMGR) catalyzes the generation of mevalonate by HMG-Co A (3-hydroxy-3-methylglutaryl coenzyme A), a key rate-limiting reaction that is dependent on the MVA terpene synthesis pathway. In order to help understand the molecular genetic mechanism of terpenoid synthesis in tea, a full-length cDNA sequence encoding HMG-Co A reductase (named as Cs HMGR1) was cloned from tea plant by RACE-PCR. The sequence consists of 1 979 bp, containing a complete 1 722 bp open reading frame encoding 573 amino acids. The putative encoded protein has 80% -82% sequence identity with the homologous proteins of rubber tree, Eclipta prostrata, ginseng, litchi, American ginseng, Salvia miltiorrhiza, Luo Han Guo and longan. The phylogenetic tree was constructed using the catalytic domain of Cs HMGR1 and HMGR homologous proteins from other species, indicating that it belongs to the class I HMGR family of eukaryotes. Structural analysis showed that Cs HMGR1 contains two transmembrane domains and is presumed to be located on the endoplasmic reticulum similar to other eukaryotic homologous proteins. It contains two HMG-Co A binding sites, two NADPH binding sites, four A conserved catalytically active residue and a phosphorylation site indicate that phosphorylation / dephosphorylation is likely also an important way of regulating its activity. Expression analysis showed that Cs HMGR1 had strong expression in leaf buds, leaf buds and flower buds of “Da Ye Long”. Its expression regulation and physiological activity may have an important influence on tea quality, and on the basis of its function analysis, it may be used as a basis for tea quality identification and breeding.