Isolation and bacterial expression of a sesquiterpene synthase cDNA clone from peppermint (Mentha x piperita, L.) that produces the aphid alarm pheromone (E)-beta-farnesene

(E)-beta-Farnesene is a sesquiterpene semiochemical that is used extensively by both plants and insects for communication. This acyclic olefin is found in the essential oil of peppermint (Mentha x piperita) and can be synthesized from farnesyl diphosphate by a cell-free extract of peppermint secretory gland cells. A cDNA from peppermint encoding (E)-beta-farnesene synthase was cloned by random sequencing of an oil gland library and was expressed in Escherichia coli. The corresponding synthase has a deduced size of 63.8 kDa and requires a divalent cation for catalysis (K-m for Mg2+ approximate to 150 mu M; K-m for Mn2+ approximate to 7 mu M). The sesquiterpenoids produced by the recombinant enzyme, as determined by radio-GC and GC-MS, are (E)-beta-farnesene (85%), (Z)-beta-farnesene (8%), and delta-cadinene (5%) with the native C15 substrate farnesyl diphosphate (K-m approximate to 0.6 mu M; V-rel = 100) and Mg2+ as cofactor, and (E)-beta-farnesene (98%) and (Z)-beta-farnesene (2%) with Mn2+ as cofactor (V-rel = 80). With the C-10 analog, GDP, as substrate (K-m = 1.5 mu M; V-rel = 3 with Mg2+ as cofactor), the monoterpenes limonene (48%), terpinolene (15%), and myrcene (15%) are produced.