Genome-Guided Discovery and Heterologous Biosynthesis of Alkylresorcinols by Collaborating Highly Reducing and Type...

The rice sheath rot pathogens Sarocladium attenuatum and Sarocladium oryzae share a conserved biosynthetic gene cluster (sarc), which encodes colocalized highly reducing polyketide synthases (HR-PKSs) and type III polyketide synthases (T3PKSs). Heterologous expression of the sarc cluster in the Aspergillus nidulans strain LO8030 led to the production of six previously unreported alkylresorcinols, sarocladones A-D (1-4) and H-I (5-6), along with three putative artifacts arising from 4, sarocladones E-G (4a-4c). Biological screening revealed that 1 and 4c both exhibit mild cytotoxicity against murine NS-1 myeloma cells, with IC₅₀ values of 13 μM and 9 μM, respectively. In addition, 1, 3, 6 and 7 displayed antiphagocytotic activity against THP1 macrophages. Subsequent bioinformatic analysis identified a homologous biosynthetic gene cluster (col) in the genome of the fungal plant pathogen Colletotrichum fructicola. To expand the structural diversity of alkylresorcinols, we employed a gene-mixing strategy, coexpressing the HR-PKS gene colA with the T3PKS gene sarcB in A. nidulans. This resulted in the production of two new sarocladone analogues, collecladones A (7) and B (8), lacking the C-2-C-3 double bond present in the sarocladones. These findings establish HR-PKS-T3PKS collaboration as an underexplored source of fungal chemical diversity.