Predominantly involved in monoterpene (C10) biosynthesis. Using GPP as substrate, the major product is (E)-beta-ocimene with minor amounts of (Z)-beta-ocimene and myrcene. Using FPP as substrate, could also be able to synthesize in vitro sesquiterpenes (C15) with (E,E)-alpha-farnesene as the major product and with (Z,E)-alpha-farnesene and (E,E)-beta-farnesene as minor products. (2E,6E)-farnesyl diphosphate = (3E,6E)-alpha-farnesene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Expressed exclusively in flowers. By coronalon. Also induced in response to the caterpillar P.xylostella feeding. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). No formation of (E)-beta-ocimene detected. Belongs to the terpene synthase family. Tpsb subfamily. Has been shown to be a pseudogene in cv. Columbia (AC P0CJ42) due to a naturally occurring frameshift at position 65 in this strain. The sequence shown is from strain cv. Wassilewskija.