title: MEKK1, MKK1/MKK2 and MPK4 function together in a mitogen-activated protein kinase cascade to regulate innate immunity in plants.
abstract: Mitogen-activated protein kinase (MAPK) cascades play important roles in regulating plant innate immune responses. In a genetic screen to search for mutants with constitutive defense responses, we identified multiple alleles of mpk4 and mekk1 that exhibit cell death and constitutive defense responses. Bimolecular fluorescence complementation (BiFC) analysis showed that both MPK4 and MEKK1 interact with MKK1 and MKK2, two closely related MAPK kinases. mkk1 and mkk2 single mutant plants do not have obvious mutant phenotypes. To test whether MKK1 and MKK2 function redundantly, mkk1 mkk2 double mutants were generated. The mkk1 mkk2 double mutant plants die at seedling stage and the seedling-lethality phenotype is temperature-dependent. Similar to the mpk4 and mekk1 mutants, the mkk1 mkk2 double mutant seedlings accumulate high levels of H2O2, display spontaneous cell death, constitutively express Pathogenesis Related (PR) genes and exhibit pathogen resistance. In addition, activation of MPK4 by flg22 is impaired in the mkk1 mkk2 double mutants, suggesting that MKK1 and MKK2 function together with MPK4 and MEKK1 in a MAP kinase cascade to negatively regulate innate immune responses in plants.
authors.affiliation: College of Biological Sciences, China Agricultural University, Beijing 100094, China.
authors.forename: Minghui
authors.initials: M
authors.lastname: Gao
authors.forename: Jinman
authors.initials: J
authors.lastname: Liu
authors.forename: Dongling
authors.initials: D
authors.lastname: Bi
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Zhang
authors.forename: Fang
authors.initials: F
authors.lastname: Cheng
authors.forename: Sanfeng
authors.initials: S
authors.lastname: Chen
authors.forename: Yuelin
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D016923:Cell Death; D018506:Gene Expression Regulation, Plant; D006861:Hydrogen Peroxide / Q000378:metabolism; D007113:Immunity, Innate; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D050505:Mutant Proteins
chemical_list: D029681:Arabidopsis Proteins; D050505:Mutant Proteins; D006861:Hydrogen Peroxide; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D048369:MAP Kinase Kinase 1; C488959:MKK2 protein, Arabidopsis; D020929:Mitogen-Activated Protein Kinase Kinases