Methyltransferase; part of the gene cluster that mediates the biosynthesis of the mycotoxin fusarin C (PubMed:23932525). Within the cluster, FUS1, FUS2, FUS8 and FUS9 are sufficient for fusarin production (PubMed:23932525). The roles of the other FUS members are yet undetermined (PubMed:23932525). The fusarin C synthetase FUS1 is responsible for the condensation of one acetyl-coenzyme A (CoA) unit with six malonyl-CoA units and the amide linkage of the arising heptaketide and homoserine, subsequently releasing the first intermediate, prefusarin, as an alcohol with an open ring structure (PubMed:23932525). The cytochrome P450 monooxygenase FUS8 participates in multiple oxidation processes at carbon C-20 and is able to use the FUS1 product as substrate, resulting in formation of 20-hydroxy-prefusarin (PubMed:23932525). This reaction seems to be essential before the 2-pyrrolidone ring closure can be catalyzed by FUS2, generating 20-hydroxy-fusarin (PubMed:23932525). FUS8 is able to further oxidizes carbon C-20 after ring closure, resulting in the formation of carboxy-fusarin C (PubMed:23932525). As the last step, FUS9 methylates the hydroxyl group at C-21 to generate fusarin C (PubMed:23932525). Fusarin C can then rearrange to epi-fusarin C, the (z)-isomers, and fusarin A and fusarin D (PubMed:23932525). Binds 1 Mg(2+) ion per subunit. Mycotoxin biosynthesis. Expressed under high amounts of nitrogen via regulation by GLN1 (PubMed:23932525). Moreover, components of the fungal-specific velvet complex VEL1, VEL2 and LAE1 act also as positive regulators of expression (PubMed:20572938, PubMed:23932525). Finally, expression is induced under acidic conditions in a PACC-independent manner (PubMed:23932525). Accumulates carboxy-fusarins (PubMed:23932525). Belongs to the methyltransferase superfamily. Type-7 methyltransferase family.