Functional analysis of CBL-interacting protein kinases 15 (StCIPK15) in response to salt and heat stress in potato (Solanum tuberosum L.).

Potato (Solanum tuberosum L.), a staple crop, is highly susceptible to environmental stressors such as high salinity and elevated temperatures. Calcineurin B-like (CBL) proteins and CBL-interacting protein kinases (CIPKs) form sensor-response complexes that regulate plant growth, development, differentiation, and stress responses. In this study, the differential expression of 14 StCBL genes and 27 StCIPK genes under salt and heat stress conditions was assessed by quantitative real-time PCR (qRT-PCR). Our experimental findings demonstrated that the salt and heat stressors significantly induced the upregulation of StCIPK15 at specific time points. Laser confocal microscopy revealed that the StCIPK15-EGFP fusion protein localized to the membrane and nucleus. Interactions between StCIPK15 and specific StCBL proteins (StCBL1, StCBL2, StCBL4, StCBL6, and StCBL9) were confirmed using yeast two-hybrid (Y2H) assays. These interactions were further validated through bimolecular fluorescence complementation (BiFC) assays. Transgenic potato plants overexpressing StCIPK15 (OE-1, OE-2, and OE-6) and StCIPK15 knockdown plants (Ri-2, Ri-4, and Ri-5) were generated. Phenotypic analysis revealed significant differences in growth parameters, such as plant height and biomass, between transgenic and non-transgenic (NT) potato plants under NaCl and high-temperature stresses. Overexpression of StCIPK15 enhanced physiological resilience. This was evidenced by elevated proline content, upregulated StP5CS expression, boosted SOD/CAT/POD activities and transcripts of StSOD/StCAT/StPOD, alongside reduced relative conductivity, HO/MDA accumulation, and ProDH1 expression. Conversely, StCIPK15 knockdown plants showed the opposite outcomes. Furthermore, transgenic potato plants demonstrated notable enhancements in photosynthetic efficiency, including higher net photosynthetic rates, increased stomatal conductance, elevated transpiration rates, and improved water-use efficiency relative to non-transgenic lines, which indicates that StCIPK15 enhances photosynthetic efficiency. Overall, these findings enhance our knowledge of the biological mechanisms that determine how StCIPK15 regulates salt and heat tolerance in potato plants.