title: Disruption of PAMP-induced MAP kinase cascade by a Pseudomonas syringae effector activates plant immunity mediated by the NB-LRR protein SUMM2.
abstract: Pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) serves as a primary plant defense response against microbial pathogens, with MEKK1, MKK1/MKK2, and MPK4 functioning as a MAP kinase cascade downstream of PAMP receptors. Plant Resistance (R) proteins sense specific pathogen effectors to initiate a second defense mechanism, termed effector-triggered immunity (ETI). In a screen for suppressors of the mkk1 mkk2 autoimmune phenotype, we identify the nucleotide-binding leucine-rich repeat (NB-LRR) protein SUMM2 and find that the MEKK1-MKK1/MKK2-MPK4 cascade negatively regulates SUMM2-mediated immunity. Further, the MEKK1-MKK1/MKK2-MPK4 cascade positively regulates basal defense targeted by the Pseudomonas syringae pathogenic effector HopAI1, which inhibits MPK4 kinase activity. Inactivation of MPK4 by HopAI1 results in activation of SUMM2-mediated defense responses. Our data suggest that SUMM2 is an R protein that becomes active when the MEKK1-MKK1/MKK2-MPK4 cascade is disrupted by pathogens, supporting the hypothesis that R proteins evolved to protect plants when microbial effectors suppress basal resistance.
authors.affiliation: National Institute of Biological Sciences, Zhongguancun Life Science Park, Beijing, People's Republic of China.
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Zhang
authors.forename: Yaling
authors.initials: Y
authors.lastname: Wu
authors.forename: Minghui
authors.initials: M
authors.lastname: Gao
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Qing
authors.initials: Q
authors.lastname: Kong
authors.forename: Yanan
authors.initials: Y
authors.lastname: Liu
authors.forename: Hongping
authors.initials: H
authors.lastname: Ba
authors.forename: Jianmin
authors.initials: J
authors.lastname: Zhou
authors.forename: Yuelin
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016923:Cell Death; D004252:DNA Mutational Analysis; D054884:Host-Pathogen Interactions; D020935:MAP Kinase Signaling System; D020125:Mutation, Missense; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology*; D057865:Plant Immunity; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D044224:Pseudomonas syringae / Q000502:physiology*; D051192:Receptors, Pattern Recognition / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D051192:Receptors, Pattern Recognition; C573316:SUMM2 protein, Arabidopsis; D011494:Protein Kinases