Despite extensive documentation on major physiological changes occurring at the ripening onset (véraison) of grape berry development, the genetic mechanisms controlling these changes remain poorly understood. It is largely admitted that ripening initiation is a combination of various factors involving internal and external signals. This long-term project will exploit a new genetic model, the microvine, which is more amenable for genetic engineering, and by using this genetic approach, we hope to determine the role of ARF4 in the control of ripening initiation and its likely influence on fruit composition towards maturity.