Functional Analysis of GarCIPK8 from Gossypium aridum Conferring Salt Stress Tolerance in Gossypium hirsutum

Soil salinization is a major abiotic stress factor restricting global agricultural production. The CBL-CIPK signaling network, comprising calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs), plays a critical role in plant adaptation to salt stress. Here, we focused on GarCIPK8, a CIPK gene previously isolated from the diploid wild cotton Gossypium aridum, and generated its overexpressing transgenic lines in G. hirsutum through Agrobacterium-mediated transformation. Under 300 mmol/L NaCl treatment, transgenic plants showed markedly enhanced growth performance, with greater height and biomass accumulation than the wild type, and these differences increased with the duration of salt exposure, reaching a maximum at 30 d. This phenotypic advantage was associated with enhanced activities of superoxide dismutase (SOD) and peroxidase (POD), together with significantly reduced malondialdehyde (MDA) content. Specifically, at 3 d of salt stress, the transgenic lines exhibited significantly higher SOD activity than the wild type, while POD activity was markedly higher at both 1 d and 3 d. Ion content analysis revealed distinct distribution patterns between transgenic and wild-type plants. At 3 d and 7 d, transgenic roots accumulated significantly less Na+, whereas Na+ content in stems and leaves was substantially higher. In parallel, at 15 d, the transgenic lines showed significantly elevated root and stem K+ levels, as well as increased root Ca2+ content at the early stage of salt treatment (1 d and 3 d). Transcriptomic analysis further supported these phenotypic and physiological changes, as differentially expressed genes (DEGs) were significantly enriched in Gene Ontology (GO) terms related to antioxidant activity, peroxidase activity, and oxidative stress response, as well as in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways including calcium ion binding, metal ion transport, transporter activity, ABC transporters, and plant hormone signal transduction. These results demonstrate that GarCIPK8 enhances salt tolerance in G. hirsutum by synergistically regulating ion homeostasis and antioxidant defense, providing a valuable genetic resource for cotton breeding.