Involved in the biosynthesis of valencene, a major volatile emitted from flowers of grapevine. Can use farnesyl diphosphate as substrate, but not geranyl diphosphate or geranylgeranyl diphosphate. Produces mainly (+)-valencene and (-)-7-epi-alpha-selinene along with five minor products. (2E,6E)-farnesyl diphosphate = (+)-valencene + diphosphate (2E,6E)-farnesyl diphosphate = (-)-7-epi-alpha-selinene + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Localizes close to lipid bodies in maturing microspores. Expressed in flowers and anthers. Detected inside the pollen grains, but not in stems, leaves, tendrils, roots, seeds, pistils or caps. Expressed at prebloom in flower buds but barely detectable after anthesis and in early stages of fruit onset. Detected again two months after flowering, then increases and reaches a maximum when the fruit is at peak maturity. Also expressed in very young seeds. 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.