The MEKK1-MKK1/MKK2-MPK4 kinase cascade negatively regulates immunity mediated by a mitogen-activated protein kinase kinase kinase in Arabidopsis.
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.
National Institute of Biological Sciences, Beijing 102206, People's Republic of China.
Qing
Q
Kong
Na
N
Qu
Minghui
M
Gao
Zhibin
Z
Zhang
Xiaojun
X
Ding
Fan
F
Yang
Yingzhong
Y
Li
Oliver X
OX
Dong
She
S
Chen
Xin
X
Li
Yuelin
Y
Zhang
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000276:immunology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D048369:MAP Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D057865:Plant Immunity / Q000235:genetics / Q000502:physiology
D029681:Arabidopsis Proteins; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; D048369:MAP Kinase Kinase 1; C488959:MKK2 protein, Arabidopsis; D020929:Mitogen-Activated Protein Kinase Kinases