Dehydratase; part of the gene cluster that mediates the biosynthesis of ustilaginoidins, dimeric gamma-naphthopyrones isolated from different fungal species (PubMed:31050129). The first step in the biosynthesis of ustilaginoidins is the production of gamma-naphthopyrone precursor YWA1 by the non-reducing polyketide synthase ustP, via condensation of one acetyl-CoA starter unit with 6 malonyl-CoA units (PubMed:31050129). YWA1 is then probably substrate of the ustZ to yield norrubrofusarin via a dehydration reaction (Probable). A key enzyme in the biosynthetic pathway is the laccase ustL, which catalyzes the oxidative dimerization of norrubrofusarin to ustilaginoidin A (PubMed:31050129). It can produce the M- and P-atropisomers in varying amounts, depending on the reaction conditions (PubMed:31050129). For the biosynthesis of 3-methylustilaginoid in derivatives such as chaetochromin A, a methylated derivative of YWA1 is required (Probable). The C-methylation is considered to be catalyzed by ustM, the phosphopantetheine attachment site of which indicates that it acts on the growing polyketide chain before release of the product (Probable). For the biosynthesis of chaetochromin A, it is assumed that saturation of the D2 double bond takes place before dimerization, and is probably catalyzed by an external reductase because no candidate gene was identified within the cluster (Probable). YWA1 = H(+) + H2O + norrubrofusarin Secondary metabolite biosynthesis. Belongs to the tpcK family.