title: MEKK1 is required for MPK4 activation and regulates tissue-specific and temperature-dependent cell death in Arabidopsis.
abstract: Innate immunity signaling pathways in both animals and plants are regulated by mitogen-activated protein kinase (MAPK) cascades. An Arabidopsis MAPK cascade (MEKK1, MKK4/MKK5, and MPK3/MPK6) has been proposed to function downstream of the flagellin receptor FLS2 based on biochemical assays using transient overexpression of candidate components. To genetically test this model, we characterized two mekk1 mutants. We show here that MEKK1 is not required for flagellin-triggered activation of MPK3 and MPK6. Instead, MEKK1 is essential for activation of MPK4, a MAPK that negatively regulates systemic acquired resistance. We also showed that MEKK1 negatively regulates temperature-sensitive and tissue-specific cell death and H(2)O(2) accumulation that are partly dependent on both RAR1, a key component in resistance protein function, and SID2, an isochorismate synthase required for salicylic acid production upon pathogen infection.
authors.affiliation: Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Ichimura
authors.forename: Catarina
authors.initials: C
authors.lastname: Casais
authors.forename: Scott C
authors.initials: SC
authors.lastname: Peck
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Ken
authors.initials: K
authors.lastname: Shirasu
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000378:metabolism* / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D016923:Cell Death; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D006861:Hydrogen Peroxide / Q000737:chemistry; D047908:Intracellular Signaling Peptides and Proteins; D019751:Intramolecular Transferases / Q000502:physiology*; D048728:MAP Kinase Kinase Kinase 1 / Q000502:physiology*; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D018521:Plant Physiological Phenomena; D013696:Temperature; D014018:Tissue Distribution
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C499581:PBS2 protein, Arabidopsis; D006861:Hydrogen Peroxide; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D019751:Intramolecular Transferases; C058486:isochorismate synthase