Trichodiene synthase; part of the gene cluster that mediates the production of the antimicrobial trichothecene harzianum A (HA) that plays a role in Botrytis cinerea antagonistic activity and plant defense priming (PubMed:21642405, PubMed:24889745). The biosynthesis of harzianum A begins with the cyclization of farnesyl diphosphate to trichodiene and is catalyzed by the trichodiene synthase TRI5 (PubMed:21642405). Trichodiene undergoes a series of oxygenations catalyzed by the cytochrome P450 monooxygenase TRI4. TRI4 controls the addition of 3 oxygens at C-2, C-11, and the C-12, C-13-epoxide to form the intermediate isotrichodiol (PubMed:21642405). Isotrichodiol then undergoes a non-enzymatic isomerization and cyclization to form 12,13-epoxytrichothec-9-ene (EPT) which is further converted to trichodermol by the cytochrome P450 monooxygenase TRI11 via C-4 hydroxylation (PubMed:21642405). The last step of HA synthesis is esterification of an octatriendioyl moiety to the C-4 oxygen of trichodermol. The octatriendioyl moiety is probably produced by the polyketide synthase TRI17 and the esterification performed by the trichothecene O-acetyltransferase TRI3 (Probable). (2E,6E)-farnesyl diphosphate = diphosphate + trichodiene Some of the cofactor binding sites show unusual localization within the protein. Sesquiterpene biosynthesis; trichothecene biosynthesis. Expression is positively regulated by the cluster-specific transcription factor TRI6. Impairs the production of harzianum A and leads to the production of a larger quantity of the aspinolides B and C. Trichothecenes are sesquiterpenoid toxins that act by inhibiting protein biosynthesis. Belongs to the trichodiene synthase family.