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.

Low temperature usually results in the developmental deformity of flower organs, immensely affecting the quality of rose flowers. However, it's largely unknown about the regulatory mechanisms activated by low temperature. Here, we used a low temperature-sensitive Rosa hybrida cv. ‘Peach Avalanche’ to screen a MADS-box gene RhAGL6 via conjoint analysis between RNA sequencing (RNA-seq) and whole-genome bisulfite sequencing (WGBS). Furthermore, we found that low temperature induced the hypermethylation and elevated histone 3 lys-27 trimethylation (H3K27me3) level on the RhAGL6 promoter, leading to decreased RhAGL6 expression. In addition, RhAGL6 silencing resulted in the formation of abnormal receptacles. We also found that the levels of gibberellins (GA₃) and abscisic acid (ABA) in the receptacle under low temperature were lower and higher, respectively, than under normal temperature. Promoter activity analysis revealed that GA₃ significantly activated RhAGL6 promoter activity, whereas ABA inhibited it. Thus, we propose that RhAGL6 regulates rose receptacle development by integrating epigenetic regulation and phytohormones signaling at low temperature.