Monoterpene glucosides accumulated in Eustoma grandiflorum roots promote hyphal branching in arbuscular mycorrhizal fungi

Abstract

Host plant-derived strigolactones trigger hyphal branching in arbuscular mycorrhizal (AM) fungi, initiating a symbiotic interaction between land plants and AM fungi. However, our previous studies revealed that gibberellin-treated Eustoma grandiflorum (Gentianaceae) activates rhizospheric hyphal branching in AM fungi using unidentified molecules other than strigolactones. In this study, we analyzed independent transcriptomic data of E. grandiflorum and found that the gentiopicroside (GPS) and swertiamarin (SWM), which are characteristic monoterpene glucosides in Gentianaceae, were highly biosynthesized in gibberellin-treated E. grandiflorum roots. Moreover, these metabolites considerably promoted hyphal branching in the Glomeraceae AM fungi Rhizophagus irregularis and R. clarus. GPS treatment also enhanced R. irregularis colonization of the monocotyledonous crop Allium schoenoprasum. Interestingly, these metabolites did not provoke the germination of the root parasitic plant Orobanche minor. Altogether, our study unveiled the crucial role of GPS and SWM in activating the symbiotic relationship between AM fungi and E. grandiflorum.