Genome-Wide Identification and Characterization of the F-Box Gene Family in Cucumber Under Heat Stress

F-box proteins typically serve as substrate-recognition subunits of the SCF (SKP1-CUL1-F-box) E3 ubiquitin ligase complex and play key roles in mediating selective protein degradation and regulating diverse biological processes. Cucumber (Cucumis sativus) is a globally important vegetable crop, but it is highly sensitive to heat stress, which severely limits its yield and quality. However, the systematic characterization of CsFBX gene family and its function in thermotolerance remain unclear. Using the high-quality CLv4.0 reference genome, this study identified 175 CsFBX genes and classified them into six clades based on phylogenetic analysis. Chromosomal localization and collinearity analysis revealed that tandem duplication is the main driver of CsFBX family expansion. Promoter cis-element analysis revealed that enrichment of stress-responsive elements in CsFBX promoter regions suggests their potential involvement in abiotic stress responses. Transcriptome profiling under heat stress identified three significantly induced candidate genes: CsFBX25, CsFBX77 and CsFBX87. Transient overexpression of CsFBX25 and CsFBX77 in cucumber led to reduced chlorosis and decreased electrolyte leakage under high temperature. Taken together, this study systematically characterized the CsFBX gene family and identified candidate genes that may contribute to heat stress responses, providing a foundation for future functional investigations.