Mining an O-methyltransferase for de novo biosynthesis of physcion in Aspergillus nidulans.

Physcion is one of natural anthraquinones, registered as a novel plant-derived fungicide due to its excellent prevention of plant disease. However, the current production of physcion via plant extraction limits its yield promotion and application. Here, a pair of polyketide synthases (PKS) in emodin biosynthesis were used as probes to mining the potential O-methyltransferase (OMT) responsible for physcion biosynthesis. Further refinement using the phylogenetic analysis of the mined OMTs revealed a distinct OMT (AcOMT) with the ability of transferring a methyl group to C-6 hydroxyl of emodin to form physcion. Through introducing AcOMT, we successfully obtained the de novo production of physcion in Aspergillus nidulans. The physcion biosynthetic pathway was further rationally engineered by expressing the decarboxylase genes from different fungi. Finally, the titer of physcion reached to 64.6 mg/L in shake-flask fermentation through enhancing S-adenosylmethionine supply. Our work provides a native O-methyltransferase for physcion biosynthesis and lays the foundation for further improving the production of physcion via a sustainable route. KEY POINTS: • Genome mining of the native O-methyltransferase responsible for physcion biosynthesis • De novo biosynthesis of physcion in the engineered Aspergillus nidulans • Providing an alternative way to produce plant-derived fungicide physcion.

Cadinane-type sesquiterpenoid dimeric diastereomers hibisceusones A-C from infected stems of Hibiscus tiliaceus with cytotoxic activity against triple-negative breast cancer cells.

Three new cadinane-type sesquiterpenoid dimeric diastereomers (1-3) named hibisceusones A-C were obtained from the infected stems of Hibiscus tiliaceus. The structures were determined by NMR spectroscopy and MS techniques, and the absolute configurations were assigned by ECD and single-crystal X-ray diffraction techniques. Compounds 1-3 are diastereomers, and contain a 1,4-dioxane ring linearly fused to different cadinane-type polycyclic skeletons. This is the first time that such a structure has been identified in natural products. Compounds 1-3 exhibited cytotoxic activities, and 2 showed a significantly high anti-triple-negative breast cancer (TNBC) effect. The anti-cancer effect of compound 2 was 3-4 fold higher than that of 1 and 3. The anti-cancer effect was generated via the induction of the apoptosis of the MDA-MB-231 cells by inhibiting the PI3Kα pathway.