4-O-dimethylallyl-L-tyrosine synthase; part of the gene cluster that mediates the biosynthesis of sirodesmin PL, an epipolythiodioxopiperazine (ETP) characterized by a disulfide bridged cyclic dipeptide and that acts as a phytotoxin which is involved in the blackleg didease of canola (PubMed:15387811, PubMed:18272357, PubMed:19762440). SirD catalyzes the O-prenylation of L-tyrosine (L-Tyr) in the presence of dimethylallyl diphosphate (DMAPP) to yield 4-O-dimethylallyl-L-Tyr, and therefore represents probably the first pathway-specific enzyme in the biosynthesis of sirodesmin PL (PubMed:19762440, PubMed:21038099, PubMed:24083562). SirD can also use D-tyrosine, L-3,4-dihydroxyphenylalanine, 4-amino-l-phenylalanine and tryptophan derivatives as substrates, albeit with a lower transferase activity (PubMed:19762440, PubMed:21038099, PubMed:24083562). 4-O-dimethylallyl-L-Tyr, then undergoes condensation with L-Ser in a reaction catalyzed by the non-ribosomal peptide synthase sirP to form the diketopiperazine (DKP) backbone (PubMed:18272357). Further bishydroxylation of the DKP performed by the cytochrome P450 monooxygenase sirC leads to the production of the intermediate phomamide (PubMed:27390873). This step is essential to form the reactive thiol group required for toxicity of sirodesmin PL (PubMed:27390873). The next steps of sirodesmin biosynthesis are not well understood yet, but some predictions could be made from intermediate compounds identification (PubMed:18272357). Phomamide is converted into phomalizarine via oxidation, probably by sirT (PubMed:18272357). Further oxidation, methylation (by sirM or sirN) and reduction steps convert phomalizarine to deacetyl sirodesmin (PubMed:18272357). Finally, acetyltransferase sirH probably acetylates deacetyl sirodesmin to produce sirodesmin PL (PubMed:18272357). dimethylallyl diphosphate + L-tyrosine = 4-O-dimethylallyl-L-tyrosine + diphosphate Mycotoxin biosynthesis. Homodimer. Expression is co-regulated with the other genes from the sirodesmin cluster and corresponds with sirodesmin production (PubMed:15387811). Belongs to the tryptophan dimethylallyltransferase family.