Involved in giberellin biosynthesis (Probable) (PubMed:16307364). Catalyzes the conversion of geranylgeranyl diphosphate to the gibberellin precursor ent-copalyl diphosphate (Probable) (PubMed:16307364). (2E,6E,10E)-geranylgeranyl diphosphate = ent-copalyl diphosphate Plant hormone biosynthesis; gibberellin biosynthesis. The Asp-Xaa-Asp-Asp (DXDD) motif is important for the catalytic activity through binding to Mg(2+). Dwarf phenotype due to gibberellin-deficient mutant, displaying reduced internode lengths, foreshortened broad leaves, and unbranched tassel. Belongs to the terpene synthase family. Tpsc subfamily.