Disruption of PAMP-Induced MAP Kinase Cascade by a Pseudomonas syringae Effector Activates Plant Immunity Mediated by the NB-LRR Protein SUMM2

• Published in: Cell host & microbe 2012-03, Vol.11 (3), p.253-263
• Main Authors: Zhang, Zhibin, Wu, Yaling, Gao, Minghui, Zhang, Jie, Kong, Qing, Liu, Yanan, Ba, Hongping, Zhou, Jianmin, Zhang, Yuelin
• Format: Article
• Language: English
• Subjects: Alleles; Arabidopsis - immunology; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis Proteins - physiology; Bacterial Proteins - immunology; Bacterial Proteins - metabolism; Carrier Proteins - genetics; Carrier Proteins - metabolism; Carrier Proteins - physiology; Cell Death; DNA Mutational Analysis; Host-Pathogen Interactions; MAP Kinase Signaling System; Mutation, Missense; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Immunity; Protein Kinases - genetics; Protein Kinases - metabolism; Protein Structure, Tertiary; Pseudomonas syringae - physiology; Receptors, Pattern Recognition - metabolism
• ISSN: 1931-3128; 1934-6069
• DOI: 10.1016/j.chom.2012.01.015

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. ► The MEKK1-MKK1/MKK2-MPK4 kinase cascade is required for basal defense ► MEKK1-MKK1/MKK2-MPK4 cascade negatively regulates NB-LRR protein SUMM2-mediated immunity ► The bacterial pathogenic effector HopAI1 targets MPK4 kinase activity ► Inactivation of MPK4 by HopAI1 activates SUMM2-mediated immune responses