Cold stress can inhibit the growth of cucurbits, disrupt pollination and fertilization, induce fruit deformities, reduce plant resistance, and increase susceptibility to diseases, ultimately resulting in yield reduction, quality deterioration, or even complete crop failure. This review focuses on the main cucurbits, such as melon, cucumber, and watermelon, systematically expounding the roles of plant hormones, signaling molecules, soluble sugars, key regulatory factors, molecular mechanisms, and network interactions in their response to cold stress. Furthermore, it highlights future research directions and application potential. By analyzing existing challenges and prospective advancements in this field, the review aims to provide a comprehensive reference for facilitating genetic improvement in cold tolerance.

Melon (Cucumis melo) includes more than ten botanical groups, many of which feature netting ornamentation on the surface of mature fruit. Ripe melons display a netted skin that signifies their ripeness and readiness for consumption. Previously, we identified SKIN NETTING (CmSN), which encodes an EamA-like transporter family protein, as the candidate gene controlling fruit skin netting formation in melon, while its biological functions remain unclear. In this study, we demonstrated that the expression of the CmSN gene was considerably lower in netted melons compared to smooth-skinned melons, indicating a negative correlation between CmSN expression and netting formation. Subsequently, we employed transient overexpression and virus-induced gene silencing (VIGS) experiments to explore the role of CmSN gene during fruit development. Overexpression of the CmSN gene inhibited netting development, whereas silencing it promoted netting formation. Using heterologous transformation in tomato, we further confirmed the effect of the CmSN gene on rind texture and toughness, as these tomatoes exhibited rougher and tougher skins. Analysis with near-isogenic lines (NILs) revealed that CmSN gene-bearing fruits (NIL_CmSN) possessed significantly harder rinds than the control smooth-skinned variety HB42, underscoring the role of CmSN in enhancing rind protection. Together, our research offers essential insights into the netting formation and genetic improvement of melon fruits.

As a high-value horticultural crop, melon cultivation requires substantial labor input for plant architecture management. Dwarf architecture is a desirable trait for melon breeding, as it simplifies plant management and enables higher planting density. In this study, we identified a spontaneous dwarf mutant, HMN-d, derived from a cantalupensis melon HMN. Compared to HMN, HMN-d exhibited a 70% reduction in plant height with unchanged node number. BSA-seq mapped the mutation to a single 1.86 Mb interval on chromosome 7 containing CmER, a known regulator of melon height. A novel loss-of-function allele, Cmer-2, introducing a premature stop codon, was identified in this region of HMN-d. Linkage analysis using 1455 F₂ individuals via KASP marker developed from the Cmer-2 variant revealed complete co-segregation with the dwarf phenotype. Allelism analysis further demonstrated that Cmer-2 is allelic to Cmer-1, a previously identified loss-of-function allele of CmER. CmER knockout lines generated by gene editing recapitulated the dwarf phenotype, directly confirming that loss of CmER function is sufficient to cause dwarfism. Collectively, these findings establish Cmer-2 as the causal variant underlying the dwarf phenotype and provide valuable genetic resources for melon plant architecture improvement and for dissecting the mechanisms of height regulation.

SHN (SHINE) transcription factors belong to the AP2/ERF superfamily. They regulate cuticular wax biosynthesis and abiotic stress responses in plants, and play crucial roles in fruit netting development of cucurbit crops. However, a systematic genome-wide analysis of the SHN gene family in melon has not yet been reported. In this study, the thick-skinned melon cultivar ‘L5283’ was used as experimental material, and nine CmSHN family members were identified at the whole-genome level. We systematically analyzed their physicochemical properties, chromosomal distribution, evolutionary conservation, promoter cis-acting elements, and expression patterns under four types of stresses. The results showed that the nine CmSHN genes were unevenly distributed across six chromosomes. Extensive synteny was observed among SHN genes of cucurbit species including melon, watermelon and cucumber, with higher genomic structural conservation detected between cucumber and melon. Six categories of cis-elements were enriched in CmSHN gene promoters, namely light-responsive, hormone-responsive, stress-related, and development-associated elements, along with circadian rhythm and flavonoid biosynthesis elements. Light-responsive elements were the most abundant, suggesting that light signals may contribute to the regulation of CmSHN transcription. RT-qPCR analysis under ABA, cold, drought and salt stresses revealed that all CmSHN genes were induced to varying degrees, with obvious differences in response patterns and duration. Notably, CmSHN7 exhibited markedly higher fold induction than other family members under all four stress treatments. This study systematically characterizes the fundamental features and stress response patterns of the CmSHN family in melon, provides baseline data for elucidating the molecular mechanisms underlying wax biosynthesis and fruit netting formation, and supplies candidate genes for molecular breeding of stress resistance in cucurbit crops.