Cloning and characterization of a cDNA encoding β-amyrin synthase from petroleum plant Euphorbia tirucalli L.

Euphorbia tirucalli L., known as the petroleum plant, produces a large amount of triterpenes, such as β-amyrin. Degenerate RT-PCR based on the sequences conserved among known β-amyrin synthases led to cloning of a putative triterpene synthase cDNA, EtAS, from leaves of E. tirucalli. The deduced amino acid sequence of the EtAS cDNA showed the highest identity of 82% to the Panax ginseng β-amyrin synthase. Heterologous expression of the EtAS ORF in the methylotrophic yeast, Pichia pastoris, resulted in production of β-amyrin, revealing that the EtAS cDNA codes for a β-amyrin synthase. This is the first report of a gene involved in the triterpene synthetic pathway from Euphorbiaceae plants.