Gao Minghui, Liu Jinman, Bi Dongling, Zhang Zhibin, Cheng Fang, Chen Sanfeng, Zhang Yuelin
College of Biological Sciences, China Agricultural University, Beijing 100094, China.
Cell Res. 2008 Dec;18(12):1190-8. doi: 10.1038/cr.2008.300.
Mitogen-activated protein kinase (MAPK) cascades play important roles in regulating plant innate immune responses. In a genetic screen to search for mutants with constitutive defense responses, we identified multiple alleles of mpk4 and mekk1 that exhibit cell death and constitutive defense responses. Bimolecular fluorescence complementation (BiFC) analysis showed that both MPK4 and MEKK1 interact with MKK1 and MKK2, two closely related MAPK kinases. mkk1 and mkk2 single mutant plants do not have obvious mutant phenotypes. To test whether MKK1 and MKK2 function redundantly, mkk1 mkk2 double mutants were generated. The mkk1 mkk2 double mutant plants die at seedling stage and the seedling-lethality phenotype is temperature-dependent. Similar to the mpk4 and mekk1 mutants, the mkk1 mkk2 double mutant seedlings accumulate high levels of H2O2, display spontaneous cell death, constitutively express Pathogenesis Related (PR) genes and exhibit pathogen resistance. In addition, activation of MPK4 by flg22 is impaired in the mkk1 mkk2 double mutants, suggesting that MKK1 and MKK2 function together with MPK4 and MEKK1 in a MAP kinase cascade to negatively regulate innate immune responses in plants.
丝裂原活化蛋白激酶（MAPK）级联在调节植物先天免疫反应中发挥重要作用。在一项寻找具有组成型防御反应突变体的遗传筛选中，我们鉴定出了mpk4和mekk1的多个等位基因，这些等位基因表现出细胞死亡和组成型防御反应。双分子荧光互补（BiFC）分析表明，MPK4和MEKK1都与MKK1和MKK2相互作用，MKK1和MKK2是两个密切相关的MAPK激酶。mkk1和mkk2单突变体植株没有明显的突变表型。为了测试MKK1和MKK2是否具有冗余功能，我们构建了mkk1 mkk2双突变体。mkk1 mkk2双突变体植株在幼苗期死亡，且幼苗致死表型与温度有关。与mpk4和mekk1突变体类似，mkk1 mkk2双突变体幼苗积累高水平的H2O2，表现出自发性细胞死亡，组成型表达病程相关（PR）基因并表现出抗病性。此外，在mkk1 mkk2双突变体中，flg22对MPK4的激活受到损害，这表明MKK1和MKK2与MPK4和MEKK1一起在MAP激酶级联中发挥作用，对植物的先天免疫反应进行负调控。
