Mitogen-activated protein kinase(MAPK) cascades are highly conserved signaling modules that regulate plant immune responses. The Arabidopsis thaliana Raf-like MAPK kinase kinase ENHANCED DISEASE RESISTANCE1(EDR1) is a...Mitogen-activated protein kinase(MAPK) cascades are highly conserved signaling modules that regulate plant immune responses. The Arabidopsis thaliana Raf-like MAPK kinase kinase ENHANCED DISEASE RESISTANCE1(EDR1) is a key negative regulator of plant immunity that affects the protein levels of MKK4 and MKK5, two important MAPK cascade members, but the underlying mechanism is poorly understood. Here, genome-wide phosphorylation analysis demonstrated that the E3 ligase KEEP ON GOING(KEG) is phosphorylated in the edr1 mutant but not the wild type, suggesting that EDR1 negatively affects KEG phosphorylation. The identified phosphorylation sites in KEG appear to be important for its accumulation. The keg-4 mutant, a previously identified edr1 suppressor, enhances susceptibility to the powdery mildew pathogen Golovinomyces cichoracearum. In addition, MKK4 and MKK5 protein levels are reduced in the keg-4 mutant. Furthermore,we demonstrate that MKK4 and MKK5 associate with full-length KEG, but not with truncated KEG-RK or KEG-RKA, and that KEG ubiquitinates and mediates the degradation of MKK4 and MKK5. Taken together, these results indicate that MKK4 and MKK5 protein levels are regulated by KEG via ubiquitination, uncovering a mechanism by which plants finetune immune responses by regulating the homeostasis of key MAPK cascade members via ubiquitination and degradation.展开更多
During embryo development, the vascular precursors and ground tissue stem cells divide to renew them-selves and produce the vascular tissue, endodermal cells, and cortical cells. However, the molecular mech-anisms reg...During embryo development, the vascular precursors and ground tissue stem cells divide to renew them-selves and produce the vascular tissue, endodermal cells, and cortical cells. However, the molecular mech-anisms regulating division of these stem cells have remained largely elusive. In this study, we show that loss of function of SOMATIC EMBRYOGENESIS RECEPTOR-UKE KINASE (SERK) genes results in aberrant em-bryo development. Fewer cortical, endodermal, and vascular cells are generated in the embryos of serk1 serk2bak1 triple mutants. WUSCHEL-RELATED HOMBOBOX5 (WOXS) is ectopically expressed in vascular cells of serkl serk2 bak1 embryos. The first transverse division of vascular precursors in mid-globular em-bryos and second asymmetric division of ground tissue stem cells in early-heart embryos are abnormally altered to a longitudinal division. The embryo defects can be partially rescued by constitutively activated mitogen-activated protein kinase (MAPK) kinase kinase YODA (YDA) and MAPK kinase MKK5. Taken together, our results reveal that SERK-mediated signals regulate division patterns of vascular precursors and ground tissue stem cells, likely via the YDA-MKK4/5 cascade, during embryo development.展开更多
基金supported by grants from the National Natural Science Foundation of China (31761133017 and 31525019) to D.T。
文摘Mitogen-activated protein kinase(MAPK) cascades are highly conserved signaling modules that regulate plant immune responses. The Arabidopsis thaliana Raf-like MAPK kinase kinase ENHANCED DISEASE RESISTANCE1(EDR1) is a key negative regulator of plant immunity that affects the protein levels of MKK4 and MKK5, two important MAPK cascade members, but the underlying mechanism is poorly understood. Here, genome-wide phosphorylation analysis demonstrated that the E3 ligase KEEP ON GOING(KEG) is phosphorylated in the edr1 mutant but not the wild type, suggesting that EDR1 negatively affects KEG phosphorylation. The identified phosphorylation sites in KEG appear to be important for its accumulation. The keg-4 mutant, a previously identified edr1 suppressor, enhances susceptibility to the powdery mildew pathogen Golovinomyces cichoracearum. In addition, MKK4 and MKK5 protein levels are reduced in the keg-4 mutant. Furthermore,we demonstrate that MKK4 and MKK5 associate with full-length KEG, but not with truncated KEG-RK or KEG-RKA, and that KEG ubiquitinates and mediates the degradation of MKK4 and MKK5. Taken together, these results indicate that MKK4 and MKK5 protein levels are regulated by KEG via ubiquitination, uncovering a mechanism by which plants finetune immune responses by regulating the homeostasis of key MAPK cascade members via ubiquitination and degradation.
基金National Natural Science Foundation of China (31770312, 31530005, 31471402, 31720103902, 31270229, 31070283)the Ministry of Education (113058A. NCET-12-0249)+2 种基金the 111 Project (B16022)the Fundamental Research Funds for the Central Universities (lzujbky-2018-kb05)the Gansu Provincial Science & Technology Department (17ZD2NA015-06, 17ZD2NA016-5).
文摘During embryo development, the vascular precursors and ground tissue stem cells divide to renew them-selves and produce the vascular tissue, endodermal cells, and cortical cells. However, the molecular mech-anisms regulating division of these stem cells have remained largely elusive. In this study, we show that loss of function of SOMATIC EMBRYOGENESIS RECEPTOR-UKE KINASE (SERK) genes results in aberrant em-bryo development. Fewer cortical, endodermal, and vascular cells are generated in the embryos of serk1 serk2bak1 triple mutants. WUSCHEL-RELATED HOMBOBOX5 (WOXS) is ectopically expressed in vascular cells of serkl serk2 bak1 embryos. The first transverse division of vascular precursors in mid-globular em-bryos and second asymmetric division of ground tissue stem cells in early-heart embryos are abnormally altered to a longitudinal division. The embryo defects can be partially rescued by constitutively activated mitogen-activated protein kinase (MAPK) kinase kinase YODA (YDA) and MAPK kinase MKK5. Taken together, our results reveal that SERK-mediated signals regulate division patterns of vascular precursors and ground tissue stem cells, likely via the YDA-MKK4/5 cascade, during embryo development.
