Abscisic Acid Regulates the 3-Hydroxy-3-methylglutaryl CoA Reductase Gene Promoter and Ginsenoside Production in Panax quinquefolium Hairy Root Cultures

Abstract

<i>Panax quinquefolium</i> hairy root cultures synthesize triterpenoid saponins named ginsenosides, that have multidirectional pharmacological activity. The first rate-limiting enzyme in the process of their biosynthesis is 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). In this study, a 741 bp fragment of the <i>P. quinquefolium</i> <i>HMGR</i> gene (<i>PqHMGR</i>), consisting of a proximal promoter, 5'UTR (5' untranslated region) and 5'CDS (coding DNA sequence) was isolated. In silico analysis of an isolated fragment indicated a lack of tandem repeats, miRNA binding sites, and CpG/CpNpG elements. However, the proximal promoter contained potential <i>cis</i>-elements involved in the response to light, salicylic, and abscisic acid (ABA) that was represented by the motif ABRE (TACGTG). The functional significance of ABA on <i>P. quinquefolium HMGR</i> gene expression was evaluated, carrying out quantitative RT-PCR experiments at different ABA concentrations (0.1, 0.25, 0.5, and 1 mg·L^-1). Additionally, the effect of abscisic acid and its time exposure on biomass and ginsenoside level in <i>Panax quinquefolium</i> hairy root was examined. The saponin content was determined using HPLC. The 28 day elicitation period with 1 mg·L^-1 ABA was the most efficient for Rg2 and Re (17.38 and 1.83 times increase, respectively) accumulation; however, the protopanaxadiol derivative content decreased in these conditions.