Functional characterization of double bond reductase involved in bisbibenzyl biosynthesis in <i>Marchantia polymorpha</i>

Bisbibenzyls are a family of characteristic secondary metabolites found in liverworts. In this study, we identified a double bond reductase (DBR) involved in the biosynthesis of bisbibenzyls in Marchantia polymorpha. Phylogenetic analysis suggests that Mp1g20080, which is highly homologous to the known DBR from Marchantia paleacea, is a candidate for the MpDBR in M. polymorpha. UV-C irradiation, which induces the accumulation of bisbibenzyls, significantly increased MpDBR expression. The recombinant MpDBR exhibited double bond reduction activity against p-coumaraldehyde. Wilting and brown thalli were observed in the Mpdbr knock-out lines, and metabolite analysis confirmed the accumulation of p-coumaric acid and a decrease in lunularic acid and bisbibenzyl levels in the Mpdbr knock-out lines. Our results demonstrated that Mp1g20080 is a major DBR in the bisbibenzyl biosynthetic pathway of M. polymorpha.