Rapid modification of the insect elicitor N-linolenoyl-glutamate via a lipoxygenase-mediated mechanism on Nicotiana attenuata leaves.
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.
VanDoorn
Arjen
A
Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, Hans Knöll Strasse 8, D-07745 Jena, Germany.
Kallenbach
Mario
M
Borquez
Alejandro A
AA
Baldwin
Ian T
IT
Bonaventure
Gustavo
G
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
D003517:Cyclopentanes; D008042:Linolenic Acids; D039821:Monoterpenes; C475661:N-linolenoyl-L-glutamine; D054883:Oxylipins; D005973:Glutamine; C011006:jasmonic acid; D008084:Lipoxygenase