Glandicoline B O-methyltransferase; part of the gene cluster that mediates the biosynthesis of the mycotoxin meleagrin (PubMed:22118684, PubMed:23776469). The first stage is catalyzed by the dipeptide synthase roqA which condenses histidine and tryptophan to produce histidyltryptophanyldiketopiperazine (HTD) (PubMed:22118684, PubMed:23776469). HTD is then converted to roquefortine C through two possible pathways (PubMed:23776469). In the first pathway, prenyltransferase roqD transforms HTD to the intermediate roquefortine D, which is in turn converted to roquefortine C by the cytochrome P450 monooxygenase roqR (PubMed:23776469). In the second pathway, HTD is first converted to the intermediate dehydrohistidyltryptophanyldi-ketopiperazine (DHTD) by roqR which is then prenylated by roqD to form roquefortine C (PubMed:23776469). Roquefortine C can be further transformed to meleagrin via three more reactions including oxydation to glandicolin A by roqM, which is further reduced to glandicoline B by roqO (PubMed:23776469). Finally, glandicoline B is converted to meleagrin by the glandicoline B O-methyltransferase roqN (PubMed:22118684, PubMed:23776469). More studies identified further branching and additional metabolites produced by the roquefortine/meleagrin cluster, including roquefortine F, roquefortine L, roquefortine M, roquefortine N and neoxaline (PubMed:24225953). glandicoline B + S-adenosyl-L-methionine = H(+) + meleagrin + S-adenosyl-L-homocysteine Alkaloid biosynthesis. Expression is decreased in presence of phenylacetic acid (PAA) (PubMed:23776469). Leads to the accumulation of glandicoline B (PubMed:22118684, PubMed:23776469). Does not affect the production of roquefortine C but decreases the production of meleagrin (PubMed:22118684, PubMed:24225953,PubMed:23776469). The indole alkaloid meleagrin was shown to be a good candidate to control c-Met-dependent breast cancer proliferation, migration and invasion (PubMed:26692349). Belongs to the class I-like SAM-binding methyltransferase superfamily.