High-mobility group B (HMGB) proteins are a class of non-histone proteins associated with eukaryotic chromatin and are known to regulate a variety of biological processes in plants. However, the functions of HMGB genes in tomato (Solanum lycopersicum) remain largely unexplored. Here, we identified 11 members of the HMGB family in tomato using BLAST. We employed genome-wide identification, gene structure analysis, domain conservation analysis, cis-acting element analysis, collinearity analysis, and qRT-PCR-based expression analysis to study these 11 genes. These genes were categorized into four groups based on their unique protein domain structures. Despite their structural diversity, all members contain the HMG-box domain, a characteristic feature of the HMG superfamily. Syntenic analysis suggested that tomato SlHMGBs have close evolutionary relationships with their homologs in other dicots. The promoter regions of SlHMGBs are enriched with numerous cis-elements related to plant growth and development, phytohormone responsiveness, and stress responsiveness. Furthermore, SlHMGB members exhibited distinct tissue-specific expression profiles, suggesting their potential roles in regulating various aspects of plant growth and development. Most SlHMGB genes respond to a variety of abiotic stresses, including salt, drought, heat, and cold. For instance, SlHMGB2 and SlHMGB4 showed positive responses to salt, drought, and cold stresses. SlHMGB1, SlHMGB3, and SlHMGB8 were involved in responses to two types of stress: SlHMGB1 responded to drought and heat, while SlHMGB3 and SlHMGB8 responded to salt and heat. SlHMGB6 and SlHMGB11 were solely regulated by drought and heat stress, respectively. Under various treatment conditions, the number of up-regulated genes significantly outnumbered the down-regulated genes, implying that the SlHMGB family may play a crucial role in mitigating abiotic stress in tomato. These findings lay a foundation for further dissecting the precise roles of SlHMGB genes.

Melon (Cucumis melo L.) is an economically important horticultural crop worldwide, while its production is continuously endangered by powdery mildew (PM), a fungal disease mainly caused by Podosphaera xanthii, due to the insufficiency of disease resistant germplasms. Here, a melon recombinant inbred line (RIL) population that consisted of 188 independent individuals was obtained through the crossing of ‘SN-1’ (C. melon L. ssp. melo) and ‘YJM’ (C. melon L. ssp. agrestis), two parents with contrasting PM resistance, followed by 7-round selfings. Comprehensive phenotypic investigation revealed substantial variations in key agronomic traits among these RILs, such as stem diameters of 3.7~12.6 mm and internode lengths of 1.6~12.2 cm at the anthesis stage, as well as peduncle lengths of 0.5~9.5 cm and soluble solid content of 1.6~17.4% at the maturation stage. Particularly, 95 RILs, of which 60 and 35 belonged to thin-peel and netted types, respectively, were identified to be highly resistant to P. xnathii infection, providing new germplasms for melon improvement. Altogether, the generation of this melo-agrestis RIL population, together with the phenotypic observations, lays a solid foundation for mechanistic investigation of the traits with economic importance and could contribute to future breeding programs of melon cultivars with PM resistance.