The MEKK1-MKK1/MKK2-MPK4 kinase cascade negatively regulates immunity mediated by a mitogen-activated protein kinase kinase kinase in Arabidopsis.

Qing Kong, Na Qu, Minghui Gao, Zhibin Zhang, Xiaojun Ding, Fan Yang, Yingzhong Li, Oliver X Dong, She Chen, Xin Li, Yuelin Zhang

The Plant cell 2012 May

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In Arabidopsis thaliana, the MEKK1-MKK1/MKK2-MPK4 mitogen-activated protein (MAP) kinase cascade represses cell death and immune responses. In mekk1, mkk1 mkk2, and mpk4 mutants, programmed cell death and defense responses are constitutively activated, but the mechanism by which MEKK1, MKK1/MKK2, and MPK4 negatively regulate cell death and immunity was unknown. From a screen for suppressors of mkk1 mkk2, we found that mutations in suppressor of mkk1 mkk2 1 (summ1) suppress the cell death and defense responses not only in mkk1 mkk2 but also in mekk1 and mpk4. SUMM1 encodes the MAP kinase kinase kinase MEKK2. It interacts with MPK4 and is phosphorylated by MPK4 in vitro. Overexpression of SUMM1 activates cell death and defense responses that are dependent on the nucleotide binding-leucine-rich repeat protein SUMM2. Taken together, our data suggest that the MEKK1-MKK1/MKK2-MPK4 kinase cascade negatively regulates MEKK2 and activation of MEKK2 triggers SUMM2-mediated immune responses.

Citation

Qing Kong, Na Qu, Minghui Gao, Zhibin Zhang, Xiaojun Ding, Fan Yang, Yingzhong Li, Oliver X Dong, She Chen, Xin Li, Yuelin Zhang. The MEKK1-MKK1/MKK2-MPK4 kinase cascade negatively regulates immunity mediated by a mitogen-activated protein kinase kinase kinase in Arabidopsis. The Plant cell. 2012 May;24(5):2225-36