Light and temperature regulated terpene biosynthesis: hepatoprotective monoterpene picroside accumulation in Picrorhiza kurrooa

Abstract

Picrorhiza (Picrorhiza kurrooa) is an endangered medicinal plant with well-known hepatoprotective activity attributed to monoterpenoid picrosides. The present article details on regulatory genes of terpenoid metabolism, 3-hydroxy-3-methylglutaryl coenzyme A reductase (pkhmgr) and 1-deoxy-D-xylulose-5-phosphate synthase (pkdxs) from picrorhiza. Since no molecular information was available, these genes were cloned to full-length by degenerate primers and rapid amplification of cDNA ends, followed by cloning of the upstream sequences that showed the presence of core sequences for light and temperature responsiveness. Electrophoretic mobility shift assay confirmed binding of protein to these motifs. Expression of pkhmgr and pkdxs was up-regulated at 15 degrees C as compared to at 25 degrees C as well as under light as compared to dark conditions. Picrosides content exhibited the trend similar to gene expression. To rule out the possible limitation of carbon pool under dark condition, plantlets of picrorhiza were raised in vitro in Murashige and Skoog medium supplemented with 3% sucrose. Results showed similar up-regulation of both the genes and the higher picrosides content in in vitro raised plantlets in the presence of light. Data suggested the important roles played by light and temperature in regulating pkhmgr and pkdxs, and the picrosides level in picrorhiza.