Prenyltransferase; part of the gene cluster that mediates the biosynthesis of fusaridione A, a bright yellow trans-fused decalin-containing tetramic acid with antimicrobial activity (PubMed:23614392). The PKS module of fsdS catalyzes the formation of the polyketide unit which is then conjugated to L-tyrosine by the condensation domain of the fsdS NRPS module. Activity of the Dieckmann cyclase domain (RED) results in release of the intermediate fusaridione A (PubMed:23614392). The unstable pyrrolidinedione ring of fusaridione A is opened through a reverse-Dieckmann reaction to afford its ring-opened form (PubMed:23614392). Mycotoxin biosynthesis. Belongs to the tryptophan dimethylallyltransferase family.