Genome-guided discovery and heterologous biosynthesis of alkylresorcinols by collaborating highly reducing and type III polyketide synthases

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.