Non-reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of the bibenzoquinone oosporein, a metabolite required for fungal virulence that acts by evading host immunity to facilitate fungal multiplication in insects (PubMed:26305932). The non-reducing polyketide synthase OpS1 produces orsellinic acid by condensing acetyl-CoA with 3 malonyl-CoA units (PubMed:26305932). Orsellinic acid is then hydroxylated to benzenetriol by the hydroxylase OpS4 (PubMed:26305932). The intermediate is oxidized either nonenzymatically to 5,5'-dideoxy-oosporein or enzymatically to benzenetetrol by the oxidoreductase OpS7 (PubMed:26305932). The latter is further dimerized to oosporein by the catalase OpS5 (PubMed:26305932). OpS6 probably functions en route for protecting cells against oxidative stress by scavenging any leaked free radical form of benzenetetrol by activating the thiol group of glutathione (PubMed:26305932). acetyl-CoA + 2 H(+) + 3 malonyl-CoA = 3 CO2 + 4 CoA + orsellinate Secondary metabolite biosynthesis. Expression is positively regulated by the oosporein cluster specific regulator OpS3 that binds the promoter at a 5'-CGGA-3' motif (PubMed:26305932). Expression is negatively regulated by the global transcription factor Msn2 that binds the stress-response element 5'-AGGGG-3' (PubMed:26305932). Multidomain protein; including a starter unit:ACP transacylase (SAT) that selects the starter unit; a ketosynthase (KS) that catalyzes repeated decarboxylative condensation to elongate the polyketide backbone; a malonyl-CoA:ACP transacylase (MAT) that selects and transfers the extender unit malonyl-CoA; a product template (PT) domain that controls the immediate cyclization regioselectivity of the reactive polyketide backbone; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm (By similarity). The release of the polyketide chain from the non-reducing polyketide synthase is mediated by the thioesterase (TE) domain localized at the C-ter of the protein (By similarity). Leads to the loss of oosporein production (PubMed:26305932).