This research addresses the fundamental question of what is the genetic basis of the ripening initiation in grape berries. Compelling evidence gathered for the past three years by the Deluc’s group has led to identify one regulatory gene (Auxin-Response Factor 4) that might be involved in determining the entry of a grape berry into the ripening phase (véraison). The objectives of the research project are 1) to validate the role of Auxin-Response Factor 4 (ARF4) on the timing of ripening initiation using genetically engineered microvines, 2) to identify the ripening-related genes that are on the direct and indirect influence of ARF4 with a major focus on genes associated with Abscisic Acid (ABA) and sugar metabolisms, and 3) to determine changes in fruit composition in grape berries with delayed or advances ripening due to the over-expression or the silencing of ARF4. As a first step of the project, we are currently cloning the sequence of ARF4 gene into plasmid vectors to generate transgenic plants that will constitutively accumulate the ARF4 protein or will eliminate the presence of the protein in the transgenic lines.