Involved in defensive oleoresin formation in conifers in response to insect attack or other injury. Involved in monoterpene (C10) olefins biosynthesis. (2E)-geranyl diphosphate = (4S)-limonene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Terpene metabolism; oleoresin biosynthesis. By wounding. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). The conserved 70-Arg-Arg-71 motif may play a role in the isomerization step of the terpenoid cyclization reaction sequence. Belongs to the terpene synthase family. Tpsd subfamily.