Genome-wide analysis of the SOS2 gene family in melon (Cucumis melo L.) and functional characterization of MELO3C010334 in response to salt stress

Soil salinity is a major abiotic stress that severely restricts the growth, yield, and quality of melon (Cucumis melo L.). The Salt Overly Sensitive (SOS) signaling pathway plays a crucial role in plant salt tolerance, in which SOS2 acts as a central kinase regulating ion homeostasis and stress responses. However, the SOS2 gene family in melon remains unclear. Here, we identified 20 SOS2 genes (CmSOS2) in the melon genome, distributed unevenly across nine chromosomes. All CmSOS2 proteins contain conserved pkinase and NAF domains, essential for kinase activity and calcium sensor binding. Phylogenetic analysis classified the genes into seven clades, indicating evolutionary conservation across species. Promoter analysis revealed abundant cis-elements associated with light, hormone, and stress responses. Expression profiling under salt stress and hormone treatments showed significant upregulation of MELO3C010334 and MELO3C007208, suggesting their pivotal roles in stress signaling. Further functional validation confirmed that overexpression of MELO3C010334 significantly enhanced salt tolerance in melon, promoted root growth, and improved Na+/K+ homeostasis in roots. This study represents the first systematic characterization of the genomic features and expression patterns of the SOS2 gene family in melon, and clarifies the positive regulatory role of MELO3C010334 under salt stress. It provides important genetic resources and a theoretical basis for further understanding the molecular mechanisms of salt tolerance and for genetic improvement of salt tolerance in melon.