Methyltransferase; part of the gene cluster that mediates the biosynthesis of the mycotoxin fusarin C (PubMed:17121404, PubMed:22652150). Within the cluster, FUS1, FUS2, FUS8 and FUS9 are sufficient for fusarin production (By similarity). The roles of the other FUS members are yet undetermined (By similarity). 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:17121404). 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 (By similarity). This reaction seems to be essential before the 2-pyrrolidone ring closure can be catalyzed by FUS2, generating 20-hydroxy-fusarin (By similarity). FUS8 is able to further oxidizes carbon C-20 after ring closure, resulting in the formation of carboxy-fusarin C (By similarity). As the last step, FUS9 methylates the hydroxyl group at C-21 to generate fusarin C (By similarity). Fusarin C can then rearrange to epi-fusarin C, the (z)-isomers, and fusarin A and fusarin D (By similarity). Binds 1 Mg(2+) ion per subunit. Mycotoxin biosynthesis. Belongs to the methyltransferase superfamily. Type-7 methyltransferase family.