Cloning and characterization of beta-amyrin synthase from Bupleurum kaoi

[[abstract]]Bupleurum kaoi, an important medicinal plant, contains various phytosterols and bioactive triterpene saikosaponins. Saikosaponins have been reported to have pharmacological properties such as anti-inflammatory and anti-hepatotoxic effects. The gene encoding B. kaoi beta-amyrin synthase was characterized to elucidate its role in triterpene biosynthesis. A putative BkβAS cDNA was obtained with RT-PCR using degenerate primers based on the conserved sequences. The deduced amino acid sequence of BkβAS showed 83% identity to the beta-amyrin synthase of Panax ginseng. The open reading frame containing 2286 bp was ligated into the yeast expression plasmid, pYES6, under the control of GAL1 promoter and introduced into Saccharomyces cerevisiae (ATCC 4021900). Analyses of accumulated products in the selected transformants revealed that the BkβAS encodes a beta-amyrin synthase. Northern blot analysis demonstrated that the transcript levels are higher in plants more than 5 months old, mainly in roots and leaves. The level of BkβAS transcripts was increase by exogenous application of methyl jasmonate to 4 month old plants, but not to the adventitious root culture. Overexpression and silencing of the BkβAS gene may contribute to the manipulation of sterol and triterpene contents in plants.[[fileno]]2050133030003[[department]]生科