Physiological responses of grapevine (<i>Vitis vinifera</i> L.) developing buds to drought stress: A transcriptomic analysis

Drought poses a significant challenge to grapevine (Vitis vinifera L.) development, impacting both physiological processes and yield. This study explores the transcriptomic responses of developing buds of cv. Merlot grapevine to drought, focusing on key genetic and physiological adaptations. Grapevines were subjected to a controlled water deficit during critical phenological stages, especially for floral induction, and the transcriptomic analysis revealed complex adaptive mechanisms at the molecular level. Water stress notably affected the grapevine’s growth and caused significant leaf necrosis. Bud fertility measurements in the following year showed a differential impact of drought according to node position along the shoot, with basal (nodes 1–3) and distal buds (nodes 8–10) more affected than the central ones. This caused a decrease in the number and weight of grape inflorescences, particularly at basal nodes. Transcriptomic data from nodes 2, 5, and 10 showed significant changes in gene expression, dealing with stress responses, hormonal signalling, and metabolic processes. Notably, upregulation of genes related to calcium signalling, ROS (Reactive Oxygen Species) detoxification, and cell wall modification was observed, which are crucial for maintaining cellular integrity under stress conditions. Differential expression of genes regulating flowering further highlighted the impact of drought on reproductive development. Post-stress recovery analyses showed a partial reversal of stress-induced transcriptomic changes, with significant upregulation of genes involved in photosynthesis and lipid metabolism, suggesting a complex recovery mechanism. These findings may contribute to a deeper understanding of the physiological and molecular basis of drought tolerance in grapevine, providing insights into strategies for improving grapevine resilience in the face of increasing water scarcity due to climate change.