Regulatory Mechanisms and Developmental Dynamics of Flower Bud Differentiation in Grapevine (Vitis spp.)

Flower bud differentiation in grapevine (Vitis spp.) is a complex, multi-seasonal process that determines yield potential and fruit quality in this perennial woody crop. This review integrates morphological, physiological, hormonal, and molecular perspectives to elucidate the regulatory mechanisms underlying floral initiation, inflorescence primordium formation, and floral organ differentiation. Grapevine buds exhibit a hierarchical structure with primary, secondary, and tertiary components, where reproductive fate is primarily determined by the primary bud during the first growing season, followed by reactivation after dormancy. Flower bud differentiation is tightly coordinated by nutrient availability, particularly the balance between carbon and nitrogen, and by dynamic hormonal interactions, including gibberellins, cytokinins, abscisic acid, and auxins, which collectively govern meristem fate and inflorescence patterning. At the molecular level, floral organ identity is governed by the ABCDE model, MADS-box transcription factors, miRNA modules, and light- and temperature-responsive regulatory networks that integrate environmental cues with internal signals, orchestrating the precise timing and patterning of floral organogenesis. Recent advances in transcriptomics, hormone profiling, and co-expression network analyses have revealed species-specific adaptations in grapevine that link dormancy, bud burst, and flowering. Understanding these mechanisms provides theoretical and practical insights for optimizing viticultural management, improving bud fruitfulness, and enhancing reproductive performance and resilience under variable climatic conditions.