title: A Proteasome-regulated glycogen synthase kinase-3 modulates disease response in plants.
abstract: Glycogen synthase kinase-3 (GSK-3) is a key player in various important signaling pathways in animals. The activity of GSK-3 is known to be modulated by protein phosphorylation and differential complex formation. However, little information is available regarding the function and regulation of plant GSK-3/shaggy-like kinases (GSKs). Analysis of the in vivo kinase activity of MsK1, a GSK from Medicago sativa, revealed that MsK1 is active in healthy plants and that MsK1 activity is down-regulated by the elicitor cellulase in a time- and dose-dependent manner. Surprisingly, cellulase treatment triggered the degradation of the MsK1 protein in a proteasome-dependent manner suggesting a novel mechanism of GSK-3 regulation. Inhibition of MsK1 kinase activity and degradation of the protein were two successive processes that could be uncoupled. In a transgenic approach, stimulus-induced inhibition of MsK1 was impeded by constant replenishment of MsK1 by a strong constitutive promoter. MsK1 overexpressing plants exhibited enhanced disease susceptibility to the virulent bacterial pathogen Pseudomonas syringae. MAP kinase activation in response to pathogen infection was compromised in plants with elevated MsK1 levels. These data strongly suggest that tight regulation of the plant GSK-3, MsK1, may be important for innate immunity to limit the severity of virulent bacterial infection.
authors.affiliation: Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter, Dr. Bohrgasse 9, A-1030 Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Wrzaczek
authors.forename: Wilfried
authors.initials: W
authors.lastname: Rozhon
authors.forename: Claudia
authors.initials: C
authors.lastname: Jonak
mesh_terms: D002480:Cellulase / Q000378:metabolism; D015536:Down-Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D000455:Medicago sativa / Q000201:enzymology* / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D044224:Pseudomonas syringae / Q000378:metabolism / Q000472:pathogenicity; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C116919:mitogen and stress-activated protein kinase 1; D038362:Glycogen Synthase Kinase 3; D002480:Cellulase; D046988:Proteasome Endopeptidase Complex