Guard cells possess a calcium-dependent protein kinase that phosphorylates the KAT1 potassium channel.
Increasing evidence suggests that changes in cytosolic Ca2+ levels and phosphorylation play important roles in the regulation of stomatal aperture and as ion transporters of guard cells. However, protein kinases responsible for Ca2+ signaling in guard cells remain to be identified. Using biochemical approaches, we have identified a Ca(2+)-dependent protein kinase with a calmodulin-like domain (CDPK) in guard cell protoplasts of Vicia faba. Both autophosphorylation and catalytic activity of CDPK are Ca2+ dependent. CDPK exhibits a Ca(2+)-induced electrophoretic mobility shift and its Ca(2+)-dependent catalytic activity can be inhibited by the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. Antibodies to soybean CDPK alpha cross-react with CDPK. Micromolar Ca2+ concentrations stimulate phosphorylation of several proteins from guard cells; cyclosporin A, a specific inhibitor of the Ca(2+)-dependent protein phosphatase calcineurin enhances the Ca(2+)-dependent phosphorylation of several soluble proteins. CDPK from guard cells phosphorylates the K+ channel KAT1 protein in a Ca(2+)-dependent manner. These results suggest that CDPK may be an important component of Ca2+ signaling in guard cells.
Li
J
J
Department of Biology, Pennsylvania State University, University Park 16802, USA.
Lee
Y R
YR
Assmann
S M
SM
D002118:Calcium / Q000378:metabolism; D002384:Catalysis; D010766:Phosphorylation; D059828:Plant Cells; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000201:enzymology* / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011494:Protein Kinases / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases
D002118:Calcium; D010940:Plant Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases