The perennial woody plant Hydrangea arborescens ‘Annabelle’ is of great research valuedue to its unique mechanism  of flower development that occurs in the current year, resulting indecorative flowers that can be enjoyed for a relatively long period of time. However, the mechanisms underlying the regulation of current-year flower development in H. arborescens ‘Annabelle’ are still not fully understood. In this study, we conducted an associated analysis to explore the core regulating network in H. arborescens ‘Annabelle’ by combining phenological observations, physiological assays,transcriptome comparisons across seven flower developmental stages. Through this analysis,we constructed a gene co-expression network (GCN) based on the highest reciprocal rank (HRR), using 509 differentially expressed genes (DEGs) identified from seven flowering-related pathways, aswell as the biosynthesis of eight flowering-related phytohormonessignal transduction in thetranscriptomic analysis. According to the analysis of the GCN, we identified 14 key genes with the highest functional connectivity that played critical roles in specific development stages. We confirmed that 135 transcription factors (AP2/ERF, bHLH, CO-like, GRAS, MIKC, SBP, WRKY) were highly co-expressed with the 14 key genes, indicating their close associations with the development of current-year flowers. We further proposed a hypothetical model of a gene regulatory network for thedevelopment of the whole flower. This model suggested that the photo period, aging,gibberellin pathways, along with the phytohormones abscisic acid (ABA), gibberellin (GA), brassinosteroid (BR),jasmonic acid (JA), work synergistically to promote the floral transition. Additionally, auxin,GA, JA, ABA,salicylic acid (SA) regulated the blooming process by involving the circadian clock. Cytokinin (CTK), ethylene (ETH),SA were key regulators that affected flower senescence.Additionally, several floral integrators (HaLFY, HaSOC1-2, HaAP1, HaFULL, HaAGL24, HaFLC, etc.) were dominant contributors to the development of H. arborescens flowers. Overall, this research provides a comprehensive understanding of the dynamic mechanism  underlying the entire process of current-year flower development, thereby offering valuable insights for further studies on the flower development of H. arborescens ‘Annabelle’.

DOI：10.3390/plants12244103