title: Harpin induces activation of the Arabidopsis mitogen-activated protein kinases AtMPK4 and AtMPK6.
abstract: Mitogen-activated protein kinases (MAPKs) are key enzymes that mediate adaptive responses to various abiotic and biotic stresses, including pathogen challenge. The proteinaceous bacterial elicitor harpin (secreted by Pseudomonas syringae pv syringae) activates two MAPKs in suspension cultures of Arabidopsis var. Landsberg erecta. In this study, we show that harpin and exogenous hydrogen peroxide (H(2)O(2)) activate myelin basic protein kinases in Arabidopsis leaves. Using anti-AtMPK4 and anti-AtMPK6 antibodies, we identify the harpin-activated MAPKs in both leaves and suspension cultures as AtMPK4 and AtMPK6, and show that H(2)O(2), generated by Arabidopsis cells in response to challenge with harpin, activates only AtMPK6. However, treatments with catalase, which removes H(2)O(2), or diphenylene iodonium, which inhibits superoxide and H(2)O(2) production, do not inhibit harpin-induced activation of AtMPK4 or AtMPK6. In addition, activation of AtMPK4 but not AtMPK6 is inhibited by the MAPK kinase inhibitor PD98059. Neither harpin nor H(2)O(2) has any effect on AtMPK4 or AtMPK6 gene expression. In addition, the expression of AtMEKK1, AtMEK1, or AtMKK2, previously shown to be potential functional partners of AtMPK4, were not affected by either harpin or H(2)O(2) treatments. These data suggest that harpin activates several signaling pathways, one leading to stimulation of the oxidative burst and others leading to the activation of AtMPK4 or AtMPK6.
authors.affiliation: Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Desikan
authors.forename: J T
authors.initials: JT
authors.lastname: Hancock
authors.forename: K
authors.initials: K
authors.lastname: Ichimura
authors.forename: K
authors.initials: K
authors.lastname: Shinozaki
authors.forename: S J
authors.initials: SJ
authors.lastname: Neill
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology*; D029681:Arabidopsis Proteins; D001425:Bacterial Outer Membrane Proteins / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D038362:Glycogen Synthase Kinase 3; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000032:analysis; D015398:Signal Transduction; D013481:Superoxides / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D001425:Bacterial Outer Membrane Proteins; D018749:RNA, Plant; C075462:harpin protein, Erwinia amylovora; D013481:Superoxides; C087295:HrpZ protein, Pseudomonas syringae; D006861:Hydrogen Peroxide; D002374:Catalase; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C086369:ATMPK1 protein, Arabidopsis; C436292:AtMPK4 protein, Arabidopsis; C086370:MPK2 protein, Arabidopsis; C436293:MPK6 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C436294:MEKK1 protein, Arabidopsis; D038362:Glycogen Synthase Kinase 3