Monoterpene synthase (TPS) involved in the biosynthesis of monoterpene natural products, components of the chemical defense arsenal (PubMed:17557809). Catalyzes the conversion of (2E)-geranyl diphosphate (GPP) into 1,8-cineole, and, as minor products, alpha-terpineol, beta-pinene, alpha-pinene, sabinene and myrcene (PubMed:17557809). (2E)-geranyl diphosphate + H2O = 1,8-cineole + diphosphate (2E)-geranyl diphosphate = alpha-pinene + diphosphate (2E)-geranyl diphosphate = beta-pinene + diphosphate (2E)-geranyl diphosphate + H2O = (S)-alpha-terpineol + diphosphate (2E)-geranyl diphosphate = beta-myrcene + diphosphate (2E)-geranyl diphosphate = diphosphate + sabinene Binds 3 Mg(2+) or Mn(2+) ions per subunit. kcat is 3.18 min(-1) with (2E)-geranyl diphosphate as substrate. Secondary metabolite biosynthesis; terpenoid biosynthesis. Monomer. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsb subfamily.