Unraveling the Mechanisms Initiating Veraison in Grape Berries

Veraison represents a pivotal transition point in grape berry ripening, driven by a cascade of temporally coordinated physiological and molecular events. Studies have shown that the onset of veraison is initially triggered by a decline in cell turgor, regulated by osmotic potential and water status, which subsequently leads to fruit softening. This softening process is accompanied by extensive cell wall remodeling, establishing a structural basis for enhanced sugar influx. A rapid accumulation of sugars follows, acting not only as metabolic substrates but also as signaling molecules that synergize with abscisic acid (ABA) to activate transcriptional programs, including the induction of anthocyanin biosynthesis that drives skin color change. ABA accumulates at the early stages of veraison and functions as a key hormonal regulator initiating the ripening process. In contrast, auxin (IAA) and gibberellin (GA) levels decline prior to veraison, thereby releasing their inhibitory effects on ripening. Environmental factors such as water availability, light, and temperature significantly influence the timing and intensity of veraison by modulating hormonal signaling pathways. The initiation of grape berry ripening exemplifies a multilayered regulatory network that progresses through turgor signaling, hormonal regulation, metabolic reprogramming, and transcriptional activation, thereby providing a mechanistic framework for understanding non-climacteric fruit ripening. offering a mechanistic framework for understanding non-climacteric fruit ripening. This review provides an integrated perspective on the initiation mechanism of veraison, offering theoretical insights and practical implications for improving grape quality and vineyard management.