The Arabidopsis MEKK1‐MKK1/MKK2‐MPK4 kinase cascade is monitored by the nucleotide‐binding leucine‐rich‐repeat immune receptor SUMM2. Disruption of this kinase cascade leads to activation of SUMM2‐mediated immune responses. MEKK2, a close paralog of MEKK1, is required for defense responses mediated by SUMM2, the molecular mechanism of which is unclear. In this study, we showed that MEKK2 serves as a negative regulator of MPK4. It binds to MPK4 to directly inhibit its phosphorylation by upstream MKKs. Activation of SUMM2‐mediated defense responses induces the expression of MEKK2 , which in turn blocks MPK4 phosphorylation to further amplify immune responses mediated by SUMM2. Intriguingly, MEKK2 locates in a tandem repeat consisting of MEKK1 , MEKK2 and MEKK3 , which was generated from a recent gene duplication event, suggesting that MEKK2 evolved from a MAPKKK to become a negative regulator of MAP kinases.

中文翻译：

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MEKK2抑制拟南芥中MAP激酶的激活。

拟南芥的MEKK1-MKK1 / MKK2-MPK4激酶级联反应由核苷酸结合的亮氨酸丰富的重复免疫受体SUMM2监控。该激酶级联反应的破坏导致SUMM2介导的免疫反应的激活。SUKK2介导的防御反应需要MEKK2的近端同源物MEKK2，其分子机制尚不清楚。在这项研究中，我们表明MEKK2充当MPK4的负调节剂。它与MPK4结合以直接抑制上游MKK的磷酸化。SUMM2介导的防御反应的激活诱导了MEKK2的表达，进而阻止了MPK4的磷酸化，从而进一步放大了SUMM2介导的免疫反应。有趣的是，MEKK2位于由MEKK1组成的串联重复序列中，MEKK2和MEKK3是从最近的基因复制事件中产生的，表明MEKK2从MAPKKK进化成为MAP激酶的负调控子。