A 45-kDa protein kinase related to mitogen-activated protein kinase is activated in tobacco cells treated with a phorbol ester.
Phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinases in animals, elicits the transient activation of a 45-kDa protein kinase in tobacco cell-suspension cultures. The 45-kDa protein kinase preferentially phosphorylates myelin basic protein (MBP), a general substrate for MAPK. Studies using cycloheximide indicated that protein synthesis is not required for the activation of the kinase. Treatment of tobacco cell extracts containing the activated kinase with either serine/threonine-specific or tyrosine-specific protein phosphatase abolished the kinase activity, which consequently appears to be regulated by phosphorylation. By using an immune complex kinase assay with antibodies specific for stress-responsive MAPKs, we show that the PMA-activated kinase is immunologically related to the wound-induced protein kinase (WIPK), and not to the salicylic acid-induced protein kinase (SIPK), two representative members of the tobacco MAPK family, known to be activated by extracellular stimuli. Furthermore, the activated kinase was recognized by phospho-specific MAPK antibodies. Collectively, these results indicate that phorbol ester promotes the activation of a 45-kDa protein kinase related to WIPK in tobacco cells. Activation of WIPK in response to PMA is associated with protein phosphorylation but not with an increase in protein level.
Baudouin
E
E
Signaux et Messages Cellulaires chez les Végétaux, UMR 5546 CNRS/Université P. Sabatier, Pĵle de Biotechnologie Végétale, Castanet-Tolosan, France.
Charpenteau
M
M
Ranjeva
R
R
Ranty
B
B
D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D008970:Molecular Weight; D010766:Phosphorylation; D010940:Plant Proteins / Q000187:drug effects / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013314:Stress, Mechanical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013912:Threonine / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D014443:Tyrosine / Q000378:metabolism
D010940:Plant Proteins; D013912:Threonine; D014443:Tyrosine; D012694:Serine; D003513:Cycloheximide; D020928:Mitogen-Activated Protein Kinases; C113423:WIPK protein, Nicotiana tabacum; C404401:salicylic acid-induced protein kinase kinase; D020929:Mitogen-Activated Protein Kinase Kinases; D013755:Tetradecanoylphorbol Acetate