Characterization of the Potato KHD Gene Family: Evolutionary Conservation, Hormone-Responsive Expression, and Core Members Mediating Abiotic Stress Tolerance

RNA-binding proteins (RBPs), specifically those containing K Homology (KH) domains, are critical for post-transcriptional regulation and abiotic stress responsiveness in plants. However, systematic characterization of the KHD gene family in potato (Solanum tuberosum L.) remains unreported. Here, we identified 83 StKHD genes unevenly distributed across 12 potato chromosomes, which clustered into five subgroups with conserved gene structures and motif compositions. Most StKHD proteins were predicted to localize to the nucleus, confirmed experimentally for StKHD-41 via transient expression in Nicotiana benthamiana. Collinearity analysis revealed 23, 22, 19, and 4 orthologous pairs with Arabidopsis, tomato, pepper, and tobacco, respectively. Promoter analysis showed distribution of hormone- and stress-responsive cis-elements, while interaction network analysis predicted 39 StKHDs interacting with 137 proteins. Tissue-specific profiling revealed broad expression of several StKHDs, and specific members displayed consistent expression changes under abiotic stresses, correlating with TC-rich repeat enrichment. RT-qPCR validated that StKHD-41 responded rapidly to JA, moderately to SA/GA, and slowly to ABA, with significant upregulation under drought and salt stress by day 2. This study provides a foundation for understanding StKHD functions and identifies targets for enhancing potato stress resistance.