Molecular Cloning and Expression of Squalene Epoxidase from a Medicinal Plant, Bupleurum chinense

作     者：Ke Gao Jie-sen Xu Jing Sun Yan-hong Xu Jian-he Wei Chun Sui 

作者机构：Institute of Medicinal Plant Development Chinese Academy of Medical Sciences 

出 版 物：《Chinese Herbal Medicines》 (中草药（英文版）)

年 卷 期：2016年第8卷第1期

页      面：67-74页

学科分类：1008[医学-中药学(可授医学、理学学位)] 0710[理学-生物学] 07[理学] 09[农学] 071007[理学-遗传学] 0901[农学-作物学] 090102[农学-作物遗传育种] 10[医学] 

基　　金：Open Research Fund of State Key Laboratory Breeding Base of Systematic Research Development and Utilization of Chinese Medicine Resources 2014KFJJ05 

主　　题：Bupleurum chinense gene functional expression methyl jasmonate phytosterols quantitative real time PCR squalene epoxidase triterpenoids Umbelliferae 

摘      要：Objective In plant, squalene epoxidase （SE） catalyzes the first oxygenation step in the biosynthetic pathway of triterpenoid and phytosterol, representing one of the rate-limiting enzymes in this pathway. Bupleurum chinense is an important medicinal herb with its major active constituents such as triterpenoid saponins and saikosaponins. In order to obtain the series of enzymatic genes involved in saikosaponin biosynthesis, a cDNA of SE, designated BcSEI, was cloned from B. chinense. Methods The BcSEI gene was cloned by homology-based PCR and 5＇/3＇ RACE methods from the adventitious roots of B. chinense. The physical and chemical parameters of BcSE1 protein were predicted by protparam. In order to discover hints in amino acid sequences on the dominant functions in the biosynthesis of saponin or phytosterol, sequences of SE from other plants were downloaded from NCBI for sequences alignment and phylogenetic analysis. BcSEI was cloned into a yeast mutant KLNI （MATa, ergl.＇：URA3, leu2, ura3, and trpl） to verify the enzyme activity of BcSE1. Additionally, the tissue-specific expression and methyl jasmonate （MeJA） inducibility of BcSEI were investigated using quantitative real-time PCR. Results The predicted protein of BcSE1 is highly similar to SEs from other plants sharing amino acid sequence identities of up to 88%. The BcSEI can functionally complement with yeast SE gene （ERGI） when expressed in the KLNI mutant （MATa, ergl：：URA3, leu2, ura3, and trpl）. Using as controls with ^-amyrin synthase （G-AS） which is presumed to catalyze the first committed step in saikosaponin biosynthesis and a cycloartenol synthase （CAS） relating to the phytosterol biosynthesis, the transcript of BcSE1 was significantly elevated by MeJA in adventitious roots of B. chinenseand the transcript of BcSElwas most abundant in the fruits and flowers of plants, followed by that in the leaves and roots, and least in stems. Conclusion It is the first time to illustrate the molecular information of SE