Subcellular targeting of nine calcium-dependent protein kinase isoforms from Arabidopsis.
Calcium-dependent protein kinases (CDPKs) are specific to plants and some protists. Their activation by calcium makes them important switches for the transduction of intracellular calcium signals. Here, we identify the subcellular targeting potentials for nine CDPK isoforms from Arabidopsis, as determined by expression of green fluorescent protein (GFP) fusions in transgenic plants. Subcellular locations were determined by fluorescence microscopy in cells near the root tip. Isoforms AtCPK3-GFP and AtCPK4-GFP showed a nuclear and cytosolic distribution similar to that of free GFP. Membrane fractionation experiments confirmed that these isoforms were primarily soluble. A membrane association was observed for AtCPKs 1, 7, 8, 9, 16, 21, and 28, based on imaging and membrane fractionation experiments. This correlates with the presence of potential N-terminal acylation sites, consistent with acylation as an important factor in membrane association. All but one of the membrane-associated isoforms targeted exclusively to the plasma membrane. The exception was AtCPK1-GFP, which targeted to peroxisomes, as determined by covisualization with a peroxisome marker. Peroxisome targeting of AtCPK1-GFP was disrupted by a deletion of two potential N-terminal acylation sites. The observation of a peroxisome-located CDPK suggests a mechanism for calcium regulation of peroxisomal functions involved in oxidative stress and lipid metabolism.
Dammann
Christian
C
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Ichida
Audrey
A
Hong
Bimei
B
Romanowsky
Shawn M
SM
Hrabak
Estelle M
EM
Harmon
Alice C
AC
Pickard
Barbara G
BG
Harper
Jeffrey F
JF
D000215:Acylation; D017360:Arabidopsis / Q000166:cytology* / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D020675:Peroxisomes / Q000201:enzymology; D018517:Plant Roots / Q000201:enzymology; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction
D007527:Isoenzymes; D011494:Protein Kinases; D002118:Calcium