Cloning and Molecular Analysis of cDNA Encoding Cycloartenol Synthase from Centella asiatica (L.) Urban

cDNA for oxidosqualene cyclase was cloned by a homology-based PCR method and sequenced from Centella asiatica. In a sequences analysis, the putative polypeptide of C. asiatica cycloartenol synthase (CaCYS) deduced from the 2,274 bp nucleotide sequence, consisted of 758 amino acids and had a molecular mass of 86.3 kD. The predicted amino acid sequence exhibited high homology to that of PNX (cycloartenol synthase) from Panax ginseng ($89\%$). Southern blot analysis suggests that CaCYS may be present in one copy of the C. asiatica genome. If methyl jasmonate (MJ) is applied exogenously to plants, not only triterpene saponins are accumulated in tissues, but also it produces effects such as growth inhibition and the promotion of ethylene production. In order to investigate the effect of MJ and thidiazuron (TDZ), a cytokinin that plays a role as an antisenescence agent in several plants, on the level of CaCYS mRNA, we performed northern blot analysis. When MJ is alone treated by adding to culture medium, CaCYS transcripts were inhibited. However, sustained levels of the expression of CaCYS, by adding TDZ to the medium despite MJ treatments, were demonstrated in C. asiatica leaves.