Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of sordarial, a salicylic aldehyde structurally related to the phytotoxin pyriculol. The most interesting aspect of this pathway is formation of an aromatic product from the highly reducing polyketide synthase srdA. SrdA synthesizes a reduced polyketide chain from one molecule of acetyl-CoA and five molecules of malonyl-CoA. The polyketide chain is then reductively released as an aldehyde. The oxidoreductases srdC, srdD and srdE then oxidize one of the hydroxy groups to facilitate the intramolecular aldol condensation, followed by dehydration to yield a salicylic aldehyde. This aldehyde can undergo facile reduction by endogenous reductases to yield the alcohol 1-hydroxy-2-hydroxymethyl-3-pent-1,3-dienylbenzene. The flavin-dependent srdI counteract against the propensity of the aldehydes to be reduced under physiological conditions and is responsible for reoxidizing 1-hydroxy-2-hydroxymethyl-3-pent-1,3-dienylbenzene back to the salicylic aldehyde. This salicylic aldehyde is then selectively epoxidized by the cupin-domain-containing oxidoreductase srdB to yield the epoxide, which can be hydrolyzed stereoselectively by the hydrolase srdG to give the final product sordarial