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. 2012 Mar 15;11(3):253-63.
doi: 10.1016/j.chom.2012.01.015.

Disruption of PAMP-induced MAP kinase cascade by a Pseudomonas syringae effector activates plant immunity mediated by the NB-LRR protein SUMM2

Zhibin Zhang  1 , Yaling Wu, Minghui Gao, Jie Zhang, Qing Kong, Yanan Liu, Hongping Ba, Jianmin Zhou, Yuelin Zhang
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Free article

Disruption of PAMP-induced MAP kinase cascade by a Pseudomonas syringae effector activates plant immunity mediated by the NB-LRR protein SUMM2

Zhibin Zhang et al. Cell Host Microbe. .
Free article

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.

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