National Institute of Biological Sciences, Beijing 102206, People's Republic of China.
Plant Cell. 2012 May;24(5):2225-36. doi: 10.1105/tpc.112.097253. Epub 2012 May 29.
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.
在拟南芥中，MEKK1-MKK1/MKK2-MPK4 丝裂原活化蛋白（MAP）激酶级联反应抑制细胞死亡和免疫反应。在 mekk1、mkk1 mkk2 和 mpk4 突变体中，程序性细胞死亡和防御反应被持续激活，但 MEKK1、MKK1/MKK2 和 MPK4 负调控细胞死亡和免疫的机制尚不清楚。在 mkk1 mkk2 的抑制子筛选中，我们发现抑制子 mkk1 mkk2 1（summ1）的突变不仅在 mkk1 mkk2 中，而且在 mekk1 和 mpk4 中也抑制细胞死亡和防御反应。SUM1 编码 MAP 激酶激酶激酶 MEKK2。它与 MPK4 相互作用，并在体外被 MPK4 磷酸化。SUMM1 的过表达激活细胞死亡和防御反应，该反应依赖于核苷酸结合富含亮氨酸重复蛋白 SUMM2。总之，我们的数据表明，MEKK1-MKK1/MKK2-MPK4 激酶级联反应负调控 MEKK2，并且 MEKK2 的激活触发 SUMM2 介导的免疫反应。
