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

(E)-β-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)-β-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 Mg(2+ )≈ 150 μM; K(m )for Mn(2+ )≈ 7 μM). The sesquiterpenoids produced by the recombinant enzyme, as determined by radio-GC and GC-MS, are (E)-β-farnesene (85%), (Z)-β-farnesene (8%), and δ-cadinene (5%) with the native C15 substrate farnesyl diphosphate (K(m )≈ 0.6 μM; V(rel )= 100) and Mg(2+ )as cofactor, and (E)-β-farnesene (98%) and (Z)-β-farnesene (2%) with Mn(2+ )as cofactor (V(rel )= 80). With the C(10) analog, GDP, as substrate (K(m) = 1.5 μM; V(rel )= 3 with Mg(2+ )as cofactor), the monoterpenes limonene (48%), terpinolene (15%), and myrcene (15%) are produced.