摘要：Phytosterols and triterpenes are synthesized by oxidosqualene cyclases (OSCs) via the isoprenoid pathway. Here, GsAS1 —a full-length β-amyrin synthase cDNA isolated from Gentiana straminea M AXIM. —was characterized. Its open reading frame consists of 2268 bp, predicted to encode a 756 residue protein containing four QW and one Asp-Cys-Thr-Ala-Glu (DCTAE) motifs, which are both well conserved among known triterpene synthases. The deduced GsAS1 peptide sequence shares 76.2% homology with that of Panax ginseng β-amyrin synthase. A phylogenetic analysis showed that GsAS1 is closely related to other plant OSCs, and particularly to the β-amyrin synthases. When the GsAS1 sequence was heterologously expressed in Escherichia coli , an 88 kDa gene product was produced, and this reacted with the appropriate antibody. The sequence was also heterologously expressed in the Pichia pastoris yeast. GsAS1 is expressed in a tissue-specific manner, with its expression in the leaf being ca. 4.5-fold than that in the root, and nearly three-fold than that in the stem. GsAS1 expression was up-regulated by treatment with methyl jasmonate (MeJA) over a period from 6 h to 10 d post treatment. The accumulation oleanolic acid increased after induction by MeJA.
