Modular Design of Picroside-II Biosynthesis Deciphered through NGS Transcriptomes and Metabolic Intermediates Analysis in Naturally Variant Chemotypes of a Medicinal Herb, Picrorhiza kurroa

Abstract

Picroside-II (P-II), an iridoid glycoside, has colossal therapeutic potential against numerous neurological and hepatic disorders. It is also used as an active ingredient of various commercial herbal formulations including, picroliv, available for treatment of liver ailments. Despite this, the knowledge of P-II biosynthesis remains scarce owing to its negligence in P. kurroa shoots which sets constant barrier for function validation experiments. In this study, we utilized natural variation for P-II content in stolon tissues of different P. kurroa accessions and deciphered its metabolic route by integrating metabolomics of intermediates with differential NGS transcriptomes. Upon navigating through high vs low P-II content accessions (1.3-2.6%), we have established that P-II is biosynthesized via degradation of ferulic acid to produce vanillic acid which acts as its immediate biosynthetic precursor. Moreover, the ferulic acid treatment in vitro at 150 µM concentration provided further confirmation with 2-fold rise in vanillic acid content. Interestingly, the cross-talk between different compartments of P. kurroa i.e. shoots and stolons, resolved spatial complexity of P-II biosynthesis and consequently speculated the burgeoning necessity to bridge gap between vanillic acid and P-II production in P. kurroa shoots. This work thus, offers a forward looking strategy to produce both P-I and P-II in shoot cultures, a step towards providing a sustainable production platform for these medicinal compounds via-a-vis relieving pressure from natural habitat of P. kurroa.