Acylalkylpyrone synthase that catalyzes not only the polyketide chain elongation but also the one-pot condensation of two beta-ketoacyl units to produce the 3-acyl-4-hydroxy-6-alkyl-alpha-pyrone (AcAP) scaffold, a precursor of csypyrone B (PubMed:20471846, PubMed:23290452, PubMed:24011646, PubMed:24895122, PubMed:25564614) (Probable). The enzyme reaction is initiated by the loading of acetoacetyl-CoA onto Cys-155, and subsequent thioester bond cleavage by the nucleophilic water generates the beta-keto acid intermediate, which is placed within a pocket (PubMed:25564614). The second beta-ketoacyl unit is then produced by polyketide chain elongation of fatty acyl-CoA with one molecule of malonyl-CoA, and the condensation with the beta-ketoacid generates the final products (PubMed:24895122, PubMed:25564614). Csypyrone B1 is the major product and contains a propanoic acid side-chain, whereas csypyrones B2 and B3 are minor compounds that contain butyric or pentanoic acid side-chains, respectively (PubMed:20471846, PubMed:23290452, PubMed:24011646). Homodimer. Expressed during 1-3 days of culture in DPY medium. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.