Modular Design of Picrosides Biosynthesis Unravelled through Intermediates Flux Dynamics vis a vis Expression Analysis of Pathway Genes in a Medicinal Herb Picrorhiza kurroa Royle ex Benth

Abstract

Picroside I P I and Picroside II P II are the iridoid glycosides in Picrorhiza kurroa having therapeutic potential against numerous neurological and hepatic disorders These are also used as active ingredients in various commercial herbal drugs formulations available for the treatment of liver ailments P I and P II are biosynthesized in a tissue specific manner ie shoots synthesize P I roots produce P II and stolons rhizomes produce both P I and P II Nevertheless mass propagation of P kurroa shoots through in vitro culture has been optimized but with lower yields of only P I In contrast P II was not detected in P kurroa plants grown in vitro Thus to enhance the contents of P I and P II in tissue specific manner in P kurroa it is a necessity to engineer metabolic carbon flux towards picrosides production However metabolic engineering of picrosides production remains a challenge considering the fact that biosynthetic architecture of picrosides is complex and non linear with poorly understood fluxes dynamics Consequently it is hard to decide a particular strategy for enhancing the contents of P I and P II in P kurroa through metabolic engineering Therefore in this research work we have applied metabolic flux analysis to elucidate the mechanism behind P I and P II biosynthesis in P kurroa To address this the interconnections between primary and secondary metabolism for enhanced P I production were investigated on the basis of temporal effects on expression patterns of genes catalyzing rate limiting steps in both primary and secondary metabolic pathways The results revealed associations of DXPS PMK HMGR ISPD and HK genes with P I content for the first 20 days of P kurroa growth at 15°C in vitro whereas G10H and DAHPS showed highest expression levels in 30 days grown shoots where the P I content was also maximum This indicates that G10H iridoid pathway and DAHPS shikimate phenylpropanoid pathway act in conjunction for increased P I production in P kurroa Further the in vitro feeding of cinnamic acid CA and catalpol CAT