title: Lipase activity in insect oral secretions mediates defense responses in Arabidopsis.
abstract: How plants perceive herbivory is not yet well understood. We investigated early responses of the model plant Arabidopsis (Arabidopsis thaliana) to attack from the generalist grasshopper herbivore, Schistocerca gregaria (Caelifera). When compared with wounding alone, S. gregaria attack and the application of grasshopper oral secretions (GS) to puncture wounds elicited a rapid accumulation of various oxylipins, including 13-hydroperoxy octadecatrienoic acid, 12-oxo-phytodienoic acid (OPDA), jasmonic acid, and jasmonic acid-isoleucine. Additionally, GS increased cytosolic calcium levels, mitogen-activated protein kinase (MPK3 and MPK6) activity, and ethylene emission but not the accumulation of hydrogen peroxide. Although GS contain caeliferin A16:0, a putative elicitor of caeliferan herbivores, treatment with pure, synthetic caeliferin A16:0 did not induce any of the observed responses. With mutant plants, we demonstrate that the observed changes in oxylipin levels are independent of MPK3 and MPK6 activity but that MPK6 is important for the GS-induced ethylene release. Biochemical and pharmacological analyses revealed that the lipase activity of GS plays a central role in the GS-induced accumulation of oxylipins, especially OPDA, which could be fully mimicked by treating puncture wounds only with a lipase from Rhizopus arrhizus. GS elicitation increased the levels of OPDA-responsive transcripts. Because the oral secretions of most insects used to study herbivory-induced responses in Arabidopsis rapidly elicit similar accumulations of OPDA, we suggest that lipids containing OPDA (arabidopsides) play an important role in the activation of herbivory-induced responses.
authors.affiliation: Max Planck Institute for Chemical Ecology, Department of Molecular Ecology, Jena 07745, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Schäfer
authors.forename: Christine
authors.initials: C
authors.lastname: Fischer
authors.forename: Stefan
authors.initials: S
authors.lastname: Meldau
authors.forename: Eileen
authors.initials: E
authors.lastname: Seebald
authors.forename: Ralf
authors.initials: R
authors.lastname: Oelmüller
authors.forename: Ian T
authors.initials: IT
authors.lastname: Baldwin
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006110:Grasshoppers / Q000187:drug effects / Q000201:enzymology; D007313:Insecta / Q000187:drug effects / Q000201:enzymology*; D008049:Lipase / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009055:Mouth / Q000201:enzymology*; D054883:Oxylipins / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D005030:Ethylenes; D005231:Fatty Acids, Unsaturated; D054883:Oxylipins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C025999:12-oxophytodienoic acid; C011006:jasmonic acid; C036216:ethylene; C458516:AtMPK3 protein, Arabidopsis; C436293:MPK6 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D008049:Lipase