Transcriptome Dynamics of Terminal Buds During Flower Bud Morphogenesis in Blueberry.

Background/Objectives: Flower bud morphogenesis is a critical developmental phase during which blueberry transitions from vegetative to reproductive growth, yet the transcriptome dynamics and regulatory networks within buds during this process have not been systematically characterized. Methods: Terminal buds of the rabbiteye blueberry 'Brightwell' were sampled at six time points spanning from summer shoot cessation to bud swelling and dormancy entry. RNA sequencing, trend clustering, and Pearson correlation network analyses were performed to identify potentially important genes and regulatory relationships. Results: A total of 26,302 differentially expressed genes were identified, with a major transcriptomic shift at week 15. From four major expression trends, 1050 candidate genes were selected, including 176 flowering-related genes, 770 transcription factors, and 277 hormone-related genes. Photoperiod and vernalization pathway genes (COLs, VRN1, etc.) were predominantly down-regulated, whereas age pathway genes (SPLs) and MADS-box flower development genes (FULs, AP3, PI, and SEP2, etc.) were up-regulated. The floral integrators FT and SOC1 exhibited opposite expression dynamics: SOC1 was highly expressed during the early-to-mid stage, whereas FT peaked at the late stage, with the two showing opposing co-expression and correlation patterns. This suggests stage-specific divergence between the two integrators in coordinating flower bud differentiation and dormancy entry. Multiple hormone pathways (IAA, BR, JA, and SA, etc.) converged independently onto floral regulatory hubs through their biosynthesis/metabolism and signal transduction genes, with numerous transcription factors also involved. Conclusions: These findings provide a comprehensive view of bud transcriptome dynamics and propose a molecular regulatory framework integrating flowering signals, hormones, and transcriptional cascades, offering a theoretical foundation and gene resources for blueberry breeding.