title: The biochemistry of homoterpenes--common constituents of floral and herbivore-induced plant volatile bouquets.
abstract: Volatile organic compounds emitted by plants mediate a variety of interactions between plants and other organisms. The irregular acyclic homoterpenes, 4,8-dimethylnona-1,3,7-triene (DMNT) and 4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT), are among the most widespread volatiles produced by angiosperms with emissions from flowers and from vegetative tissues upon herbivore feeding. Special attention has been placed on the role of homoterpenes in attracting parasitoids and predators of herbivores and has sparked interest in engineering homoterpene formation to improve biological pest control. The biosynthesis of DMNT and TMTT proceeds in two enzymatic steps: the formation of the tertiary C₁₅₋, and C₂₀₋ alcohols, (E)-nerolidol and (E,E)-geranyl linalool, respectively, catalyzed by terpene synthases, and the subsequent oxidative degradation of both alcohols by a single cytochrome P450 monooxygenase (P450). In Arabidopsis thaliana, the herbivore-induced biosynthesis of TMTT is catalyzed by the concerted activities of the (E,E)-geranyllinalool synthase, AtGES, and CYP82G1, a P450 of the so far uncharacterized plant CYP82 family. TMTT formation is in part controlled at the level of AtGES expression. Co-expression of AtGES with CYP82G1 at wound sites allows for an efficient conversion of the alcohol intermediate. The identified homoterpene biosynthesis genes in Arabidopsis and related genes from other plant species provide tools to engineer homoterpene formation and to address questions of the regulation and specific activities of homoterpenes in plant-herbivore interactions.
authors.affiliation: Department of Biological Sciences, 408 Latham Hall, AgQuad Lane, Virginia Tech, Blacksburg, VA 24061, USA. tholl@vt.edu
authors.forename: Dorothea
authors.initials: D
authors.lastname: Tholl
authors.forename: Reza
authors.initials: R
authors.lastname: Sohrabi
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Huh
authors.forename: Sungbeom
authors.initials: S
authors.lastname: Lee
mesh_terms: D000222:Adaptation, Physiological; D000475:Alkenes / Q000378:metabolism; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D060467:Disease Resistance; D035264:Flowers / Q000737:chemistry*; D015870:Gene Expression; D007313:Insecta; D009812:Odorants; D009822:Oils, Volatile / Q000737:chemistry*; D010935:Plant Diseases; D013729:Terpenes / Q000378:metabolism*
chemical_list: C411254:4,8-dimethyl-1,3,7-nonatriene; D000475:Alkenes; D029681:Arabidopsis Proteins; D009822:Oils, Volatile; D013729:Terpenes