VlMYB4 and VlCDF3 co-targeted the VlLOG11 promoter to regulate fruit setting in grape (Vitis vinifera L).

key messageThe VlLOG11 mediates the cytokinin signaling pathway to regulate grape fruit setting. Fruit set, as an accepted agronomic trait, is inextricably linked with fruit quality and yield. Previous studies have demonstrated that exogenous treatment with the synthetic cytokinin analog, forchlorfenuron (CPPU), significantly enhances fruit set. In this study, a significant reduction in endogenous cytokinins was found by measuring the content of cytokinins in young grape berries after CPPU treatment. LONELY GUYs (VlLOGs), a key cytokinin-activating enzyme working in the biosynthesis pathway of cytokinins, exhibited differential expression. Some differentially expressed VlLOGs genes were presented by RNA seq data and their functions and regulation patterns were further investigated. The results showed that VlLOG11 was differentially expressed in young grape berries after CPPU treatment. Overexpression of VlLOG11 in tomato increases the amount of fruit set, and upregulated the expression of genes associated with cytokinin signaling including SlHK4, SlHK5, SlHP3, SlHP4, SlPHP1, SlPHP2. VlMYB4 and VlCDF3 could regulate the expression of VlLOG11 by directly binding to its promoter in young grape berries during fruit set. These results strongly demonstrated that VlMYB4/VlCDF3-VlLOG11 regulatory module plays a key role in the process of fruit setting in grape. This provided a basis for the molecular mechanism of VlLOG11-mediated cytokinin biosynthesis in young grape fruit set.