Highly reducing polyketide synthase (HR-PKS); part of the gene cluster that mediates the biosynthesis of the neurotoxin verrucosidin, a methylated alpha-pyrone polyketide that inhibits oxidative phosphorylation in mitochondria and thereby causes neurological diseases (PubMed:34093475). The carbon backbone of verrucosidin is synthesized by the HR-PKS verA, and further modified by the other verrucodidin cluster enzymes (Probable). Binds 1 phosphopantetheine covalently. Secondary metabolite biosynthesis; terpenoid biosynthesis. Mycotoxin biosynthesis. Multidomain protein; including 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 dehydratase (DH) domain that reduces hydroxyl groups to enoyl groups; a methyltransferase (CMeT) domain responsible for the incorporation of methyl groups; a ketoreductase (KR) domain that catalyzes beta-ketoreduction steps; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm. Does not affect the ability to grow nor conidiation (PubMed:34093475). Abolishes the production of verrucosidin (PubMed:34093475). Slightly reduced virulence 7 days after the inoculation on apples cultivar Ambrosia (PubMed:34093475).