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 multipl...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 mekkl that exhibit cell death and constitutive defense responses. Bimolecular fluorescence complemen- tation （BiFC） analysis showed that both MPK4 and MEKK1 interact with MKK1 and MKK2, two closely related MAPK kinases, mkkl and mkk2 single mutant plants do not have obvious mutant phenotypes. To test whether MKK1 and MKK2 function redundantly, mkkl mkk2 double mutants were generated. The mkkl mkk2 double mutant plants die at seedling stage and the seedling-lethality phenotype is temperature-dependent. Similar to the mpk4 and mekkl mutants, the mkkl mkk2 double mutant seedlings accumulate high levels of H202, display spontaneous cell death, constitutively express Pathogenesis Related （PR） genes and exhibit pathogen resistance. In addition, activation of MPK4 by fig22 is impaired in the mkkl 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.展开更多
Over the last few years, it has become evident that reactive oxygen species （ROS） signalling plays an important role in various physiological responses, including pathogen defense and stomatal opening/closure. On th...Over the last few years, it has become evident that reactive oxygen species （ROS） signalling plays an important role in various physiological responses, including pathogen defense and stomatal opening/closure. On the other hand, ROS overproduction is detrimental for proper plant growth and development, indicating that the regulation of an appropriate redox balance is essential for plants. ROS homeostasis in plants involves the mitogen-activated protein kinase （MAPK） pathway consisting of the MAPK kinase kinase MEKK1 and the MAPK MPK4. Phenotypic and molecular analysis revealed that the MAPK kinases MKK1 and MKK2 are part of a cascade, regulating ROS and salicylic acid （SA） accumulation. Gene expression analysis shows that of 32 transcription factors reported to be highly responsive to multiple ROS-inducing conditions, 20 are regulated by the MEKK1, predominantly via the MEKK1-MKK1/2-MPK4 pathway. However, MEKK1 also functions on other as yet unknown pathways and part of the MEKK1-dependent MPK4 responses are regulated independently of MKK1 and MKK2. Overall, this analysis emphasizes the central role of this MAPK cascade in oxidative stress signalling, but also indicates the high level of complexity revealed by this signalling network.展开更多
文摘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 mekkl that exhibit cell death and constitutive defense responses. Bimolecular fluorescence complemen- tation （BiFC） analysis showed that both MPK4 and MEKK1 interact with MKK1 and MKK2, two closely related MAPK kinases, mkkl and mkk2 single mutant plants do not have obvious mutant phenotypes. To test whether MKK1 and MKK2 function redundantly, mkkl mkk2 double mutants were generated. The mkkl mkk2 double mutant plants die at seedling stage and the seedling-lethality phenotype is temperature-dependent. Similar to the mpk4 and mekkl mutants, the mkkl mkk2 double mutant seedlings accumulate high levels of H202, display spontaneous cell death, constitutively express Pathogenesis Related （PR） genes and exhibit pathogen resistance. In addition, activation of MPK4 by fig22 is impaired in the mkkl 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.
文摘Over the last few years, it has become evident that reactive oxygen species （ROS） signalling plays an important role in various physiological responses, including pathogen defense and stomatal opening/closure. On the other hand, ROS overproduction is detrimental for proper plant growth and development, indicating that the regulation of an appropriate redox balance is essential for plants. ROS homeostasis in plants involves the mitogen-activated protein kinase （MAPK） pathway consisting of the MAPK kinase kinase MEKK1 and the MAPK MPK4. Phenotypic and molecular analysis revealed that the MAPK kinases MKK1 and MKK2 are part of a cascade, regulating ROS and salicylic acid （SA） accumulation. Gene expression analysis shows that of 32 transcription factors reported to be highly responsive to multiple ROS-inducing conditions, 20 are regulated by the MEKK1, predominantly via the MEKK1-MKK1/2-MPK4 pathway. However, MEKK1 also functions on other as yet unknown pathways and part of the MEKK1-dependent MPK4 responses are regulated independently of MKK1 and MKK2. Overall, this analysis emphasizes the central role of this MAPK cascade in oxidative stress signalling, but also indicates the high level of complexity revealed by this signalling network.
