Bifunctional terpene synthase converts DMAPP and IPP, and also GGPP, into variediene as a single product (PubMed:31476106). The C-terminal prenyltransferase domain of AbVS catalyzes formation of GGPP, whereas the N-terminal terpene cyclase domain catalyzes the cyclization of GGPP to variediene (PubMed:31476106). (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Secondary metabolite biosynthesis; terpenoid biosynthesis. Hexamer. The conserved DDXXD motifs as well as the NSE/DTE motif are important for the catalytic activity, presumably through binding to Mg(2+). In the N-terminal section; belongs to the terpene synthase family. In the C-terminal section; belongs to the FPP/GGPP synthase family.