The protein kinase SOS2 activates the Arabidopsis H(+)/Ca(2+) antiporter CAX1 to integrate calcium transport and salt tolerance.
The regulation of ions within cells is an indispensable component of growth and adaptation. The plant SOS2 protein kinase and its associated Ca(2+) sensor, SOS3, have been demonstrated to modulate the plasma membrane H(+)/Na(+) antiporter SOS1; however, how these regulators modulate Ca(2+) levels within cells is poorly understood. Here we demonstrate that SOS2 regulates the vacuolar H(+)/Ca(2+) antiporter CAX1. Using a yeast growth assay, co-expression of SOS2 specifically activated CAX1, whereas SOS3 did not. CAX1-like chimeric transporters were activated by SOS2 if the chimeric proteins contained the N terminus of CAX1. Vacuolar membranes from CAX1-expressing cells were made to be H(+)/Ca(2+)-competent by the addition of SOS2 protein in a dose-dependent manner. Using a yeast two-hybrid assay, SOS2 interacted with the N terminus of CAX1. In each of these yeast assays, the activation of CAX1 by SOS2 was SOS3-independent. In planta, the high level of expression of a deregulated version of CAX1 caused salt sensitivity. These findings suggest multiple functions for SOS2 and provide a mechanistic link between Ca(2+) and Na(+) homeostasis in plants.
United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA.
Ning-Hui
NH
Cheng
Jon K
JK
Pittman
Jian-Kang
JK
Zhu
Kendal D
KD
Hirschi
D017920:Antiporters / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D017136:Ion Transport; D010940:Plant Proteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
D017920:Antiporters; D029681:Arabidopsis Proteins; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D010940:Plant Proteins; C027614:calcium-hydrogen antiporters; D012964:Sodium; C406738:SOS2 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D002118:Calcium