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 exten sively by both plants and insects for communication. This acyclic olef in is found in the essential oil of peppermint (Mentha x piperita) and can be synthesized from farnesyl diphosphate by a cell-free extract o f peppermint secretory gland cells. A cDNA from peppermint encoding (E )-beta-farnesene synthase was cloned by random sequencing of an oil gl and library and was expressed in Escherichia coli. The corresponding s ynthase 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+ appr oximate to 7 mu M). The sesquiterpenoids produced by the recombinant e nzyme, as determined by radio-GC and GC-MS, are (E)-beta-farnesene (85 %), (Z)-beta-farnesene (8%), and delta-cadinene (5%) with the native C 15 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 anal og, 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.