Demonstration and characterization of (E)-nerolidol synthase from maize:: a herbivore-inducible terpene synthase participating in (3E)-4,8-dimethyl-1,3,7-nonatriene biosynthesis

Upon herbivore attack. maize (Zea mays L.) emits a mixture of volatile compounds that attracts herbivore enemies to the plant. One of the major components of this mixture is an unusual acyclic C-11 homoterpene. (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which is also emitted by many other species following herbivore damage. Biosynthesis of DMNT has been previously shown to proceed via the sesquiterpene alcohol, (E)-nerolidol. Here we demonstrate an enzyme activity that converts farnesyl diphosphate, the universal precursor of sesquiterpenes, to (3S)-(E)-nerolidol in cell-free extracts of maize leaves that had been fed upon by Spodoptera littoralis. The properties of this (E)-nerolidol synthase resemble those of other terpene synthases. Evidence for its participation in DMNT biosynthesis includes the direct incorporation of deuterium-labeled (E)-nerolidol into DMNT and the close correlation between increases in (E)-nerolidol synthase activity and DMNT emission after herbivore damage. Since farnesyl diphosphate has many other metabolic fates, (E)-nerolidol synthase may represent the first committed step of DMNT biosynthesis in maize. However, the formation of this unusual acyclic terpenoid appears to be regulated at both the level of (E)-nerolidol synthase and at later steps in the pathway.