Early epigenetic changes are involved in bud dormancy release in grapevine

Plant phenological development is deeply influenced by temperature changes, with budbreak dates being consistently moved up by global temperature increases. In grapevine, early dormancy release might result in the advancement of all subsequent developmental stages, including ripening and harvest. Moreover, spring frost damage risk could substantially increase in several areas of the world. As a result, traditional wine production is challenged by new environmental conditions in important wine-making regions. Understanding the molecular regulation of dormancy release in buds is essential to direct breeding efforts toward the production of late-budbreak varieties better suited to the new climatic scenarios. Recent evidence collected in poplar and field-grown grapevines suggests the implication of DNA demethylation in dormancy regulation. To further describe these processes, potted plants of Cabernet Sauvignon kept in controlled conditions were studied from a transcriptomic point of view. RNA-seq revealed a wide range of significant changes concerning epigenetic regulation taking place predominantly during de-acclimation. Gene ontology analysis highlighted a consistent number of genes related to DNA methylation changes, including homologs of DNA demethylases ROS1 (Repressor of Silencing 1) and DME (DEMETER). qRT-PCR confirmed the downregulation of ROS1 and DME during 4°C exposure and a trend of increasing expression up to 18 days before budbreak. These findings indicate the occurrence of active DNA methylation changes, possibly pointing out a high metabolic activity, even though no visible phenological progression was noticed in the buds. Dedicated analyses are needed to delineate the targets of ROS1 and DME activity and detail the intricacies of epigenetic regulation within grapevine buds during dormancy release.