Expression Analysis of Key Genes for Picroside-I Production in in vitro Grown Shoots of Different Genotypes and Species of Endangered Herb Picrorhiza

Abstract

Picrorhiza kurroa Royle ex Benth and Picrorhiza scrophulariiflora Pennel are the two highly valued medicinal herbs having hepatoprotective activity along with other medicinal properties. Their medicinal importance is attributed to the presence of two major secondary metabolites, picroside-I (PI) and picroside-II (P-II). Increasing demand by herbal drug industries and endangered status of this plant necessitates the screening of natural populations for high picrosides content genotypes as well as understanding the molecular biology of picrosides biosynthesis. This is the first comparative study on in vitro propagation and P-I biosynthesis in P. scrophulariiflora and P. kurroa. Micropropagation of different P. kurroa genotypes with varying P-I content was also carried out. Explants were cultured on MS media (Murashige and Skoog, 1962) supplemented with IBA (3mg/l) + KN (1mg/l) + sucrose 3% (w/v) + agar-agar (0.8%) at two different incubation temperatures i.e. 15± 1°C and 25± 1°C and quantified by HPLC for P-I contents. Better growth and higher P-I content was observed at 15± 1°C in comparison to 25± 1°C. This is attempted for the first time where comparative expression profiling of the key genes of MEP and MVA pathway in two species was done. In addition, expression analysis of different P. kurroa genotypes was carried out. Six genes ISPD, ISPE, DXPS, MECPS, HMGS and PMK showed elevated expression levels (~5-20 folds) at 15° C in comparison to 25° C. The genes with elevated expression levels would be useful in understanding the molecular basis of P-I biosynthesis and accumulation for perusal of a systematic genetic improvement programme in Picrorhiza.