title: Direct phosphorylation and activation of a mitogen-activated protein kinase by a calcium-dependent protein kinase in rice.
abstract: The mitogen-activated protein kinase (MAPK) is a pivotal point of convergence for many signaling pathways in eukaryotes. In the classical MAPK cascade, a signal is transmitted via sequential phosphorylation and activation of MAPK kinase kinase, MAPK kinase (MKK), and MAPK. The activation of MAPK is dependent on dual phosphorylation of a TXY motif by an MKK, which is considered the sole kinase to phosphorylate and activate MAPK. Here, we report a novel regulatory mechanism of MAPK phosphorylation and activation besides the canonical MAPK cascade. A rice (Oryza sativa) calcium-dependent protein kinase (CDPK), CPK18, was identified as an upstream kinase of MAPK (MPK5) in vitro and in vivo. Curiously, CPK18 was shown to phosphorylate and activate MPK5 without affecting the phosphorylation of its TXY motif. Instead, CPK18 was found to predominantly phosphorylate two Thr residues (Thr-14 and Thr-32) that are widely conserved in MAPKs from land plants. Further analyses reveal that the newly identified CPK18-MPK5 pathway represses defense gene expression and negatively regulates rice blast resistance. Our results suggest that land plants have evolved an MKK-independent phosphorylation pathway that directly connects calcium signaling to the MAPK machinery.
authors.affiliation: Department of Plant Pathology and Environmental Microbiology, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Kabin
authors.identifier: http://orcid.org/0000-0003-0643-2456
authors.initials: K
authors.lastname: Xie
authors.affiliation: Department of Plant Pathology and Environmental Microbiology, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Jianping
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Plant Pathology and Environmental Microbiology, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Plant Pathology and Environmental Microbiology, The Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania 16802 yuy3@psu.edu.
authors.forename: Yinong
authors.identifier: http://orcid.org/0000-0002-2698-1754
authors.initials: Y
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D020082:Magnaporthe / Q000502:physiology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000276:immunology; D010766:Phosphorylation; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D057865:Plant Immunity; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D016415:Sequence Alignment; D015398:Signal Transduction; D013379:Substrate Specificity; D017871:Calcium-Calmodulin-Dependent Protein Kinases
chemical_list: D002118:Calcium; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010940:Plant Proteins; D011494:Protein Kinases; D011993:Recombinant Fusion Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases