Cis-aconitate decarboxylase-like protein; part of the gene cluster that mediates the biosynthesis of oryzines, natural products with an unusual maleidride backbone (PubMed:30104550). The two subunits of the fungal fatty acid synthase oryfasA and oryfasB probably form octenoic acid (Probable). This fatty acid is most likely activated by the acyl-CoA ligase oryP to give octenyl-CoA before the citrate synthase-like protein oryE catalyzes condensation with oxaloacetate to form tricarboxylic acid (Probable). The next steps of the pathways are conjectural, but a favorite possible route has been proposed, beginning with decarboxylation and concomitant dehydration by the decarboxylase oryM, followed by tautomerization, which may lead to the production of a diene intermediate (Probable). Reduction of this diene intermediate could give the known metabolite piliformic acid (Probable). On the pathway to oryzine B and oryzine A, however, hydroxylation of the diene by the alpha-ketoglutarate-dependent dioxygenase oryG and lactonisation by the lactonohydrolases oryH or oryL could give oryzine B directly (Probable). Finally, enoyl reduction by the dehydrogenase oryD would then convert oryzine B into oryzine A (Probable). Secondary metabolite biosynthesis. Belongs to the PrpD family.