The proper flowering time of rose (Rosa hybrida) is vital for the market value of this horticultural crop, but the mechanism regulating this trait is largely unclear. Here, we found that the transcription factor SQUAMOSA PROMOTER BINDING PROTEIN-LIKE4 (RhSPL4) positively regulates flowering time in rose. Transient silencing or overexpression transgenic rose plants of RhSPL4 exhibited delayed or early flowering, respectively. Analysis of transcriptome data from transgenic lines overexpressing RhSPL4 compared to the wild type indicated that differentially expressed genes were significantly enriched in the circadian rhythm pathway. Among the proteins encoded by these genes, RhSPL4 binds to the promoter of PSEUDO-RESPONSE REGULATOR 5-LIKE (RhPRR5L), as revealed in yeast one-hybrid, dual-Luciferase/Renilla luciferase reporter, chromatin immunoprecipitation-quantitative PCR and electrophoretic mobility shift assay. Furthermore, RhSPL4 specifically binds to the − 478 to − 441 bp region of the RhPRR5L promoter and activates its transcription. The silencing of RhPRR5L delayed flowering time in rose, resembling the phenotype of RhSPL4-silenced plants. Together, these results indicate that the RhSPL4-RhPRR5L module positively regulates flowering time in rose, laying the foundation for the genetic improvement of flowering time in this important horticultural crop.

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.