Integrated metabolomic and transcriptomic profiling reveals the key role of UDP-glycosyltransferase 73D1 (UGT73D1) in rose under UV-B irradiation

Ultraviolet B (UV–B) light affects the accumulation of secondary metabolites, especially pharmacologically important flavonoids, in many plants. However, whether UV-B irradiation influences the metabolite composition of rose (Rosa spp.) remains largely unknown. To explore the effects of UV-B on rose metabolites, we compared the physiological phenotypes of two rose cultivars, Rosa hybrida ‘Jardin de Granville’ (JDG) and Rosa damascena Mill. (DMS), under UV-B irradiation. JDG was more tolerant to UV-B exposure than DMS, with lower hydrogen peroxide content and electrolyte permeability and higher soluble protein content in leaves. To elucidate the mechanisms underlying this difference, we performed metabolome and transcriptome analyses of the two cultivars. Metabolome analysis showed that UV-B irradiation influenced the biosynthetic pathways for phenylpropanoid compounds, especially the flavonoid pathway, in both cultivars, resulting in significantly altered flavonol metabolite levels. RNA sequencing indicated that UV-B irradiation influenced plant hormone signaling and secondary metabolic pathways. Combined metabolomic and transcriptomic analysis highlighted key metabolites and associated genes in the flavonoid pathway that respond to UV-B irradiation. Simultaneously, weighted gene co-expression network analysis (WGCNA) revealed that UDP glycosyltransferase 73D1 (UGT73D1) is crucial for flavonoid biosynthesis in rose under UV-B irradiation. Indeed, knocking down UGT73D1 expression compromised the tolerance of rose to UV-B irradiation. Finally, dual-luciferase assays demonstrated that the transcription factor basic leucine-zipper 44 (bZIP44) enhances UGT73D1 expression. Together, these results reveal that UV-B irradiation promotes flavonoid biosynthesis and metabolism in rose, providing an important theoretical foundation for cultivating rose germplasm with greater value for the pharmaceutical, food, and cosmetic industries.