Discerning Regulatory Control of Picrosides Biosynthesis in a Medicinal Herb Picrorhiza kurroa Royle ex Benth

Abstract

Picrorhiza kurroa is a high altitude endangered medicinal herb possessing various therapeutic properties derived from its bioactive constituents, picrosides (P-I and II). Shoots and roots are source of P-I and II, respectively while both picrosides are found in stolons and rhizomes. P-I yield remains substantially lower than the natural habitat and P-II has been unattainable in vitro. Endangered status and low metabolite production in vitro necessitates identification of biosynthetic mechanisms and corresponding regulatory modules for planning rational modulation of picrosides content accumulation. newlineNGS transcriptomes obtained from varying conditions of picrosides content served as suitable datasets for mining molecular factors associated with control of picrosides biosynthesis. Pathway regulatory control points were explored by studying the role of miRNAs and transcription factors. Gene expression and 5 RACE analysis showed that miR-4995 was involved in down-regulation of DAHPS enzyme, a regulatory enzyme of picrosides biosynthesis. ERF-18, NAC-25, 94, 32, SUF-4 and bHLH-104 were identified as possible transcriptional activators of picrosides biosynthesis, while a down-regulatory effect of MYB-4 and WRKY- 17, 71, 40 was suggested. NAC-25, ERF-18, MYB-4 and WRKY-40 were revealed as master regulators of picrosides biosynthesis via in silico promoter analysis of important picrosides biosynthetic pathway genes. newlineComparative transcriptome analysis of varying P-I accumulating shoots for differentially expressed kinases followed by evaluation of their expression status in response to different growth conditions depicted elevated expression of 16 kinases involved in biotic/abiotic stress, wounding, hormonal response, nucleotide and carbohydrate metabolism in high P-I accumulating conditions, indicating their possible role in perceiving environmental signals for picrosides biosynthesis. Availability of a larger pool of precursors responsible for initiation of P-I biosynthesis was indicated in natural habitat shoots.