Capturing Acyltransferase(s) Transforming Final Step in the Biosynthesis of a Major Iridoid Glycoside, (Picroside-II) in a Himalayan Medicinal Herb, Picrorhiza kurroa

BackgroundPicrorhiza kurroa has been reported as an age-old ayurvedic hepatoprotection to treat hepatic disorders due to the presence of iridoids such as picroside-II (P-II), picroside-I, and kutkoside. The acylation of catalpol and vanilloyl coenzyme A by acyltransferases (ATs) is critical step in P-II biosynthesis. Since accumulation of P-II occurs only in roots, rhizomes and stolons, uprooting of this critically endangered herb has been the only source of this compound. Recently, we reported that P-II acylation likely happen in roots, while stolons serve as the vital P-II storage compartment. Therefore, developing an alternate engineered platform for P-II biosynthesis require identification of P-II specific AT/s.Methods and results In that direction, egg-NOG function annotated 815 ATs from de novo RNA sequencing of tissue culture based ‘shoots-only’ system and nursery grown shoots, roots, and stolons varying in P-II content, were cross-compared in silico to arrive at ATs sequences unique and/or common to stolons and roots. Verification for organ and accession-wise upregulation in gene expression of these ATs by qPCR has shortlisted six putative ‘P-II-forming’ ATs. Further, six-frame translation, ab initio protein structure modelling and protein-ligand molecular docking of these ATs signified one MBOAT domain containing AT with preferential binding to the vanillic acid CoA thiol ester as well as with P-II., implying that this could be potential AT decorating final structure of P-II. ConclusionOrgan-wise comparative transcriptome mining coupled with reverse transcription real time qPCR and protein-ligand docking led to the identification of an acyltransferases, contributing to the final structure of P-II.