Metabolomic-Transcriptomic analysis unravels flavonoids accumulation mechanism in ‘Tainong 1’ mango pulp under enhanced UV-B radiation

Mango (Mangifera indica L.) is one of the main economic crops in Hainan, China, prized for its distinctive flavor and high nutritional value. It is also rich in health-promoting antioxidants such as vitamin C and flavonoids. Enhanced ultraviolet-B (UV-B) radiation, a growing global environmental concern, alters plant antioxidant systems, with increased flavonoid accumulation as a common adaptive response. However, its effects on mango fruit remain largely unexplored. To investigate the antioxidant responses of mango to enhanced UV-B radiation and identify key responsive flavonoid compounds and regulatory genes, we exposed ‘Tainong 1’ mango fruits growing under natural light to 96 kJ · m-2 · d-1 of UV-B radiation to simulate high UV-B conditions. Treated fruits were smaller in size and had a pulp of a more intense yellow colour. Further, malondialdehyde content in treated fruits was higher during the phase of rapid fruit enlargement. Additionally, treated fruits showed increased sugar-acid ratios, total phenol, total flavonoid, carotenoid, and ascorbic acid contents. Furthermore, they showed significantly enhanced antioxidant activity, as measured by the FRAP, ABTS, and DPPH assays. Extensive targeted metabolomic-analysis identified flavonoids as the largest category of compounds differentially expressed in treated and control groups. Quantitative metabolomics of flavonoids identified Hyperoside, Quercimeritrin, and (-)-Catechin gallate as the key flavonoid metabolites responsive to UV-B treatment. Transcriptome analysis revealed an enrichment of the flavonoid biosynthesis pathway, with most associated differentially expressed genes showing upregulation. Furthermore, qRT-PCR analysis confirmed that the expression of the genes MiCHS7, MiCHI1, MiCHI2, MiFLS, MiF3H2, and MiF3H3 correlated with changes in key flavonoid metabolites. Indeed, correlation analysis indicated that MiCHS7, MiCHI1, MiFLS, and MiF3H3 are potential key genes involved in flavonoid accumulation under UV-B treatment. Thus, our study provides a theoretical basis for breeding for new resilient varieties and developing UV-B-resistant mango cultivation techniques.