Bifunctional terpene synthase involved in the biosynthesis of the diterpene dolasta-1(15),8-diene (PubMed:30277637). The C-terminal prenyltransferase domain of CgDS catalyzes formation of the universal precursor of diterpene, geranylgeranyl diphosphate (GGPP), whereas the N-terminal terpene cyclase domain catalyzes the cyclization of GGPP to dolasta-1(15),8-diene (PubMed:30277637). (2E,6E)-farnesyl diphosphate + isopentenyl diphosphate = (2E,6E,10E)-geranylgeranyl diphosphate + diphosphate Hexamer. The DDXXD motifs 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.