Isolation and characterization of a novel PDR-type ABC transporter gene PgPDR3 from Panax ginseng C.A. Meyer induced by methyl jasmonate

In order to screen novel genes involved in the biosynthesis and accumulation of ginsenosides in ginseng for investigating the molecular mechanism of ginsenosides accumulation, the differential expression analysis was performed by cDNA-amplified fragment length polymorphism (cDNA-AFLP) in methyl jasmonate (MeJA) treated ginseng suspension cells and untreated controls. Twenty-five transcript-derived-fragments (TDFs) were obtained and 14 of them was involved in secondary metabolite biosynthesis, transportation, signal transduction and stress response. PgTDF3 (JK974248) was detected in MeJA-treated ginseng cells and its full-length cDNA was subsequently isolated. The gene designated PgPDR3 (GenBank accession number KC013238) has 4515 bp in length containing a 4137 bp open reading frame (ORF). The deduced amino acid sequence of PgPDR3 shares high similarity to other plant pleiotropic drug resistance (PDR) transporters and have the characteristic domain of plant PDR transporter Walker A, Walker B and ABC signature both at the N- and C-terminal ends respectively. RT-PCR and quantitative real-time PCR (qRT-PCR) analysis indicated that PgPDR3 was expressed at a high level in the roots and adventitious roots compared to leaves, seeds and buds, and the expression was induced strongly by MeJA in a time-dependent manner, as it is well known MeJA is a signaling molecule that mediates the biosynthesis and accumulation of secondary metabolites. These results demonstrate a potential role of the PgPDR3 gene in the accumulation of secondary metabolites in MeJA-induced ginseng.