Sesquiterpene synthase involved in the biosynthesis of volatile compounds known for their medicinal efficacy for treating enteritis, dysentery, itch and some cancers (PubMed:23072391, PubMed:21818683). Mediates the conversion of (2E,6E)-farnesyl diphosphate (FPP) into beta-elemene, alpha-humulene, delta-cadinene and alpha-selinene (PubMed:23072391, PubMed:21818683). (2E,6E)-farnesyl diphosphate = alpha-humulene + diphosphate (2E,6E)-farnesyl diphosphate = alpha-selinene + diphosphate (2E,6E)-farnesyl diphosphate = delta-cadinene + diphosphate (2E,6E)-farnesyl diphosphate = (1S,2S,4R)-beta-elemene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Mostly expressed in roots and mature leaflets and, to a lower extent, in rachis and developing leaflets. 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.