A proposed model of VlMYB59-VlCKX4 regulatory module function during CPPU-induced grape fruit set. Left, under normal development conditions, grapes undergo physiological berry abscission resulting in a low fruit set rate. Without CPPU treatment, the VlMYB59-VlCKX4 module-mediated pathway for regulating the fruit set is not activated. Right, CPPU treatment induces the VlMYB59 gene expression. The binding of the VlMYB59 transcription factor to the cis-acting element TAACCA on the VlCKX4 promoter positively regulates the VlCKX4 expression. Gene VlCKX4 acts as a positive regulatory factor to promote fruit set. Arrows represent a positive regulatory action of one component on another.