Identification and Expression Analysis of SHN Gene Family in Melon

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.