Sesquiterpene synthase involved in the biosynthesis of volatile compounds known for their medicinal efficacy for treating enteritis, dysentery, itch and some cancers (PubMed:23072391). Mediates the conversion of (2E)-geranyl diphosphate (GPP) into (4R)-limonene (PubMed:23072391). Can only use GPP as substrate, no activity with farnesyl diphosphate (FPP) (PubMed:23072391). (2E)-geranyl diphosphate = (4R)-limonene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Expressed in roots, rachis and leaflets (PubMed:23072391). Accumulates particularly in glandular cells of the leaf rachises (PubMed:23072391). 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. Tpsa subfamily.