Molecular cloning and characterization of mevalonic acid (MVA) pathway genes and triterpene accumulation in Panax ginseng

Panax ginseng Meyer is one of the most important medicinal plants in Asia, and ginseng has attracted considerable attention worldwide. Triterpene saponins (ginsenosides) are the main bioactive compounds in P. ginseng. The isoprene units of triterpene are derived from the mevalonic acid (MVA) pathway. We cloned four genes involved in MVA pathway using rapid amplification of cDNA ends by polymerase chain reaction. Additionally, we investigated the transcript levels of 11 genes involved in the terpenoid pathway in different organs and cell suspension cultures of P. ginseng. The full-length cDNA sequences were as follows: PgHMGS (1764 bp; 1407-bp ORF), PgHMGR (1992 bp; 1722-bp ORF), PgPMK (2170 bp; 1530-bp ORF), and PgMVD (1759 bp; 1263-bp ORF). The highest expression level of all genes was found in fine roots. The total ginsenoside contents in different organs were ranked in the following descending order: leaf > fine root > lateral root > red berry > main root > petiole > stem. Campesterol and stigmasterol were detected in all organs but at different concentrations. The total phytosterol content was highest in fine root (147.8 μg/100 mg dry weight (DW)), and was lowest in the stem (86.4 μg/100 mg DW). Four enzymes in the MVA pathway were cloned and characterized in P. ginseng. Such genes play important roles in terpenoid biosynthesis and may have applications in the metabolic engineering of ginsenoside production.