Discovery and Biosynthesis of a Novel Acorane-Type Sesquiterpene from Rhynchosporium agropyri

Acoranes represent an important family of sesquiterpenes featuring a unique spiro[4.5]decane skeleton with remarkable structural diversity and extensive biological activities. In this study, genome mining of the plant pathogenic fungus Rhynchosporium agropyri enabled the identification of a small biosynthetic gene cluster (rhy) encoding sesquiterpene synthase RhyA and cytochrome P450 RhyB, which together catalyze the formation of a novel acorane-type sesquiterpene, rhyagracorone (1). Furthermore, by elucidating the biosynthetic pathway of 1, we confirmed that RhyA acts as an acora-3(4),7(8)-diene (2) synthase and further explored the critical residues for RhyA’s catalytic activity through site-directed mutagenesis. Finally, bioactivity assays revealed that compound 1 exhibited inhibitory activity against the crop pathogenic fungus Cochliobolus heterostrophus with an EC50 of 91.6 μg/mL. These findings lay an important foundation for the further discovery of acorane-type sesquiterpenes and provide a potential lead compound for the research and development of agricultural antifungal agents.