O-methyltransferase; part of the gene cluster that mediates the biosynthesis of DIF-1 (Differentiation Inducing Factor-1), a signal molecule involved in the differentiation of pstO (prestalk-O) cells (PubMed:9446571). The three-step process begins with the formation of (2,4,6-trihydroxyphenyl)-1-hexan-1-one (THPH) by the polyketide synthase StlB (PubMed:16906151). THPH is then dichlorinated by the flavin-dependent halogenase ChlA (PubMed:20231486). The last step of DIF-1 biosynthesis is the O-methylation of dichloro-THPH (or des-methyl-DIF-1) by the methyltransferase DmtA to yield DIF-1 (PubMed:9446571). (3,5-dichloro-2,4,6-trihydroxyphenyl)hexan-1-one + S-adenosyl-L-methionine = 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one + H(+) + S-adenosyl-L-homocysteine Optimum pH is 6.5-7.5. Maximally expressed in prespore cells. Detectable expression levels during aggregation stage. Maximum expression at the first-finger/slug stage. By cyclic-AMP; this induction is inhibited by DIF-1. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.