The SWEET gene family is a group of genes with important functions in plants that is mainly involved in the transport and metabolism of carbohydrate substances. In this study, 32 mango (Mangifera indica L.) SWEET genes were screened and identified at the whole-genome level through bioinformatics methods. A systematic predictive analysis was conducted on their physicochemical properties, homology relationships, phylogenetic relationships, chromosomal locations, genomic structures, promoter cis-acting elements, and transcription factor regulatory networks. Meanwhile, the transcription levels of mango SWEET genes in different varieties and at different fruit development stages were also analyzed to obtain information about their functions. These results showed that 32 mango SWEET genes were unevenly distributed on 12 chromosomes. Phylogenetic analysis divided the SWEET proteins of mango, Arabidopsis thaliana (L.) Heynh., and Oryza sativa L. into four clades; in each clade, the mango SWEET proteins were more closely related to those of Arabidopsis. Four types of cis-acting elements were also found in the promoter regions of mango SWEET genes, including light-responsive elements, development-related elements, plant hormone-responsive elements, and stress-responsive elements. Interestingly, we found that the Misweet3 and Misweet10 genes showed strong expression in different mango varieties and at different fruit development stages, and they both belonged to the fourth Clade IV (G4) in the phylogenetic tree, indicating that they play a key role in the sugar accumulation process of mango. In this study, the upstream transcription factors of Misweet3, Misweet8, Misweet9, Misweet10, Misweet17, Misweet18, Misweet19, Misweet21, Misweet23, Misweet25, Misweet27, and Misweet31, those that had high expression levels in the transcriptome data, were predicted, and transcription factors such as ERF, NAC, WRKY, MYB, and C₂H₂ were screened. The results of this study provide a new way to further study the regulation of mango SWEET family genes on sugar accumulation, highlight their potential role in fruit quality improvement, and lay an important foundation for further study of mango SWEET function and enhance mango competitiveness in fruit market.

Drought stress is a major environmental factor that adversely affects plant growth and development. Spermidine (SPD), a polyamine, plays a critical role in plant defense mechanisms against drought stress. PEG was used to simulate osmotic stress, which mimics drought conditions under controlled environments. This study investigated the effects of exogenous spermidine (SPD) on the physiological and biochemical responses of mango plants under drought stress and explored its potential mitigation mechanisms. Two-year-old ‘Renong 1’ mango seedlings were subjected to drought stress induced by polyethylene glycol (PEG 6000) at concentrations of 5%, 15%, and 25%, simulating mild, moderate, and severe drought conditions, respectively. Plants were subsequently treated with 1 mmol/L spermidine. After PEG 6000 treatment and spermidine application for 3 days, the leaf morphology, relative chlorophyll content, malondialdehyde (MDA) levels, antioxidant enzyme activities (superoxide dismutase [SOD], peroxidase [POD], catalase [CAT]), and osmotic regulators (proline, soluble sugars, and soluble proteins) were analyzed. The results demonstrated that drought stress caused leaf chlorosis, desiccation, reduced relative chlorophyll content, elevated MDA levels (indicating lipid peroxidation), enhanced antioxidant enzyme activities, increased proline and soluble sugar accumulation for osmotic regulation, and decreased soluble protein content. Exogenous spermidine treatment significantly alleviated drought-induced damage by reducing leaf chlorosis, delaying relative chlorophyll degradation (by 20.0–25.7% under moderate drought and 14.1–19.1% under severe drought), and decreasing MDA levels (by 4.8–9.5% under moderate drought and 0.8–23.7% under severe drought). Furthermore, spermidine enhanced antioxidant enzyme activities (e.g., SOD activity increased by 24.9–37.4% and POD by 74.0–104.0% under moderate drought), regulated osmotic substance accumulation (e.g., proline decreased by 21%, 26%, and 24% under mild, moderate, and severe drought, respectively), and mitigated the reduction in soluble protein content (by 6.6% under moderate drought and 10.3% under severe drought). In conclusion, exogenous spermidine mitigates drought-induced damage in mango by preserving photosynthetic capacity, enhancing the antioxidant defense system, and modulating osmotic balance. These results showed that SPD could significantly improve plant vigor or survival rate under stress. It provides a theoretical basis for water-saving cultivation of mango, improving the stress resistance of mango varieties and the application of spermidine in tropical fruit production.