A 2-oxoglutarate-dependent dioxygenase converts dihydrofuran to furan in Salvia diterpenoids

Abstract

Tanshinone IIA (TIIA), a diterpene quinone with a furan ring, is a bioactive compound found in the medicinal herb redroot sage (Salvia miltiorrhiza Bunge), in which both furan and dihydrofuran analogs are present in abundance. Progress has been made recently in elucidating the tanshinone biosynthetic pathway, including heterocyclization of the dihydrofuran D-ring by cytochrome P450s; however, dehydrogenation of dihydrofuran to furan, a key step of furan ring formation, remains uncharacterized. Here, by differential transcriptome mining, we identified six 2-oxoglutarate-dependent dioxygenase (2-ODD) genes whose expressions corresponded to tanshinone biosynthesis. We showed that Sm2-ODD14 acts as a dehydrogenase catalyzing the furan ring aromatization. In vitro Sm2-ODD14 converted cryptotanshinone to TIIA and thus was designated TIIA synthase (SmTIIAS). Furthermore, SmTIIAS showed a strict substrate specificity, and repression of SmTIIAS expression in hairy root by RNAi led to increased accumulation of total dihydrofuran-tanshinones and decreased production of furan-tanshinones. We conclude that SmTIIAS controls the metabolite flux from dihydrofuran- to furantanshinones, which influences medicinal properties of S. miltiorrhiza.