Calcium-Dependent Protein Kinase 28 Maintains Potato Photosynthesis and Its Tolerance under Water Deficiency and Osmotic Stress

Calcium-dependent protein kinases (CDPK) are implicated in signaling transduction in eukaryotic organisms. It is largely unknown whether StCDPK28 plays a role in the response to water deficiency and osmotic stress in potato plants (Solanum tuberosum L.). Potato cv. Zihuabai was cultivated under natural, moderate, and severe water deficiency conditions; to induce osmotic stress, potato plants were treated with 10% or 20% PEG. StCDPK28-overexpression and StCDPK28-knockdown plants were constructed. StCDPKs were evaluated by qRT-PCR. The subcellular location of the StCDPK28 protein was observed with confocal scanning laser microscopy. Phenotypic changes were indicated by photosynthetic activity, the contents of H(2)O(2), MDA and proline, and the activities of CAT, SOD and POD. Results showed water deficiency and osmotic stress altered StCDPK expression patterns. StCDPK28 exhibited a membrane, cytosolic and nuclear localization. Water deficiency and osmotic stress induced StCDPK28 upregulation. Photosynthetic activity was enhanced by StCDPK28 overexpression, while decreased by StCDPK2 knockdown under water deficiency and osmotic stress. StCDPK28 overexpression decreased H(2)O(2) and MDA, and increased proline, while StCDPK28 knockdown showed reverse results, compared with the wild type, in response to water deficiency and osmotic stress. StCDPK28 overexpression increased the activities of CAT, SOD and POD, while StCDPK28-knockdown plants indicated the reverse trend under water deficiency and osmotic stress conditions. Regulation of StCDPK28 expression could be a promising approach to improve the tolerance ability of potato plants in response to drought or high salt media.