title: Rapid modification of the insect elicitor N-linolenoyl-glutamate via a lipoxygenase-mediated mechanism on Nicotiana attenuata leaves.
abstract: BACKGROUND
  Some plants distinguish mechanical wounding from herbivore attack by recognizing specific constituents of larval oral secretions (OS) which are introduced into plant wounds during feeding. Fatty acid-amino acid conjugates (FACs) are major constituents of Manduca sexta OS and strong elicitors of herbivore-induced defense responses in Nicotiana attenuata plants.
  
  
  RESULTS
  The metabolism of one of the major FACs in M. sexta OS, N-linolenoyl-glutamic acid (18:3-Glu), was analyzed on N. attenuata wounded leaf surfaces. Between 50 to 70% of the 18:3-Glu in the OS or of synthetic 18:3-Glu were metabolized within 30 seconds of application to leaf wounds. This heat-labile process did not result in free alpha-linolenic acid (18:3) and glutamate but in the biogenesis of metabolites both more and less polar than 18:3-Glu. Identification of the major modified forms of this FAC showed that they corresponded to 13-hydroxy-18:3-Glu, 13-hydroperoxy-18:3-Glu and 13-oxo-13:2-Glu. The formation of these metabolites occurred on the wounded leaf surface and it was dependent on lipoxygenase (LOX) activity; plants silenced in the expression of NaLOX2 and NaLOX3 genes showed more than 50% reduced rates of 18:3-Glu conversion and accumulated smaller amounts of the oxygenated derivatives compared to wild-type plants. Similar to 18:3-Glu, 13-oxo-13:2-Glu activated the enhanced accumulation of jasmonic acid (JA) in N. attenuata leaves whereas 13-hydroxy-18:3-Glu did not. Moreover, compared to 18:3-Glu elicitation, 13-oxo-13:2-Glu induced the differential emission of two monoterpene volatiles (beta-pinene and an unidentified monoterpene) in irlox2 plants.
  
  
  CONCLUSIONS
  The metabolism of one of the major elicitors of herbivore-specific responses in N. attenuata plants, 18:3-Glu, results in the formation of oxidized forms of this FAC by a LOX-dependent mechanism. One of these derivatives, 13-oxo-13:2-Glu, is an active elicitor of JA biosynthesis and differential monoterpene emission.
authors.affiliation: Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, Hans Knöll Strasse 8, D-07745 Jena, Germany.
authors.forename: Arjen
authors.initials: A
authors.lastname: VanDoorn
authors.forename: Mario
authors.initials: M
authors.lastname: Kallenbach
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Borquez
authors.forename: Ian T
authors.initials: IT
authors.lastname: Baldwin
authors.forename: Gustavo
authors.initials: G
authors.lastname: Bonaventure
mesh_terms: D000818:Animals; D003517:Cyclopentanes / Q000378:metabolism; D005973:Glutamine / Q000031:analogs & derivatives* / Q000378:metabolism; D008042:Linolenic Acids / Q000378:metabolism*; D008084:Lipoxygenase / Q000235:genetics / Q000378:metabolism*; D018402:Manduca / Q000502:physiology*; D039821:Monoterpenes / Q000032:analysis; D054883:Oxylipins / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000201:enzymology*; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics
chemical_list: D003517:Cyclopentanes; D008042:Linolenic Acids; D039821:Monoterpenes; C475661:N-linolenoyl-L-glutamine; D054883:Oxylipins; D005973:Glutamine; C011006:jasmonic acid; D008084:Lipoxygenase