title: Identification of MAPKs and their possible MAPK kinase activators involved in the Pto-mediated defense response of tomato.
abstract: The Pto kinase mediates resistance to bacterial speck disease in tomato by activating host defenses upon recognition of Pseudomonas syringae pv. tomato strains expressing the AvrPto or AvrPtoB proteins. Previous gene-silencing experiments have indicated that mitogen activated protein kinase (MAPK) cascades play a key role downstream of the Pto kinase to activate host defense responses. Here we use biochemical methods to demonstrate that two tomato MAPKs, LeMPK2 and LeMPK3, are activated in leaves in a Pto-specific manner upon expression of AvrPto and AvrPtoB. We show that these same MAPKs are activated upon overexpression of LeMAPKKKalpha, a protein previously demonstrated to be involved in Pto-mediated immunity. We identified two phylogenetically unrelated MAPK kinases (LeMKK2 and LeMKK4) that when overexpressed in leaves elicit cell death and activate LeMPK2 and LeMPK3. In vitro analysis demonstrated that LeMKK2 and LeMKK4 each phosphorylate the same subset of three MAPKs. Together these data provide biochemical evidence for the involvement of MAPK cascades in Pto-mediated resistance.
authors.affiliation: Boyce Thompson Institute for Plant Research, Ithaca, New York 14853-1801, USA.
authors.forename: Kerry F
authors.initials: KF
authors.lastname: Pedley
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Martin
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology; D016923:Cell Death; D003001:Cloning, Molecular; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant; D007113:Immunity, Innate / Q000235:genetics*; D018551:Solanum lycopersicum / Q000235:genetics / Q000382:microbiology / Q000502:physiology*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D012231:Rhizobium / Q000378:metabolism; D013379:Substrate Specificity; D014026:Nicotiana / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; C084354:Pto protein, Lycopersicon; D017346:Protein Serine-Threonine Kinases; C458516:AtMPK3 protein, Arabidopsis; C086370:MPK2 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases