The transcription factors ERF105 and NAC72 regulate expression of a sugar transporter gene and hexose accumulation in grape

Sugar transport plays a pivotal role in determining the productivity of plants and their capacity to act as carbon sinks. In the major fruit crop grapevine (Vitis vinifera L.), the transporter gene Vitis vinifera Sugars Will Eventually be Exported Transporter 15 (VvSWEET15)is strongly expressed during berry ripening. However, the specific functions of VvSWEET15 and the mechanisms governing its transcriptional regulation remain largely unresolved. Here, we demonstrate that VvSWEET15 functions as a hexose transporter whose expression is associated with the strong sugar accumulation that starts at the véraison stage. We also characterize VvERF105 as a repressor that binds to the LTR-binding element in the VvSWEET15 promoter, thereby down-regulating its expression and inhibiting hexose accumulation at the pre-véraison stage. In contrast, VvNAC72 is an activator that binds to the VvNAC72-binding domain (CACATG) and promotes VvSWEET15 expression and hexose accumulation at post-véraison stages. Both transcription factors and VvSWEET15 are preferentially expressed in phloem cells. These results demonstrate that the balance between transcriptional activators and repressors is critical in regulating VvSWEET15 expression in sink organs. Further understanding of these processes will help improve plant productivity and their potential to be used as carbon sinks.