Evolution and functional characterization of the MdSKP8 gene as a conserved hub integrating hormone and antioxidant...

SKP1-Like genes are conserved with lineage-specific diversification; apple MdSKP8 is salt-induced, enhances transgenic apple's tolerance via ROS, hormone pathways, and interacts with F-box and thaumatin-like proteins. Soil salinization critically constrains sustainable apple production. SKP1 proteins, core components of SCF E3 ubiquitin ligases, are pivotal regulators of plant stress responses; nevertheless, their role in apple salt tolerance remains undeciphered. This study integrated evolutionary and functional genomics to investigate the SKP1-Like gene family. Phylogenetic analysis revealed conserved evolution with lineage-specific diversification between monocots and dicots; Rosaceae members formed a distinct clade shaped by both purifying and positive selection. Molecular characterization identified MdSKP8 as the closest homolog to Arabidopsis ASK2. Its expression was significantly upregulated by salt stress, and the protein localized to the nucleus and cytosol. Overexpressing MdSKP8 markedly enhanced salt tolerance in transgenic apple plants, manifested as improved root architecture and reduced reactive oxygen species accumulation. Further physiological and transcriptomic analyses showed that, under salt stress, MdSKP8 overexpression was associated with enhanced antioxidant enzyme activities, proline accumulation, and altered expression of hormone- and MAPK-related genes, suggesting its potential involvement in coordinating stress adaptation. Protein-protein interaction assays confirmed that MdSKP8 specifically interacts with F-box proteins MdAMR and MdEID-like, along with the thaumatin-like protein MdTL, respectively, forming interacting protein modules. Collectively, this study elucidates a novel mechanism wherein MdSKP8 synergistically integrates hormone signaling and antioxidant pathways to enhance salt tolerance, providing crucial insights and genetic resources for breeding stress-resistant apple cultivars.