VvbZIP60-VvERF2/VvERF104 Module Enhances Hexose Transport under Water Stress in Grape Berries

Water stress cultivation serves as an effective strategy for both water conservation and promoting sugar accumulation in grape berries (Vitis vinifera L.). However, the key sugar transporters involved and the regulatory interplay among the upstream signaling pathways remain poorly understood. In this study, we observed that moderate water stress activates sugar metabolism and significantly increases the rate of sugar accumulation. Transcriptome analysis identified a novel sugars will eventually be exported transporter (SWEET) family gene, VvSWEET14a, which we hypothesize mediates early-stage sugar accumulation under water stress. Further investigation revealed that VvSWEET14a is localized to the tonoplast and facilitates hexose accumulation. Additionally, we found that two AP2/ERF transcription factors, VvERF2 and VvERF104, directly bind to the DRE motif in the VvSWEET14a promoter, activating its transcription. In grape calli and berries, the expression levels of VvERF2 and VvERF104 strongly correlate with VvSWEET14a transcript abundance, ultimately influencing the glucose and fructose contents. Furthermore, VvbZIP60 (a basic leucine zipper transcription factor) interacts with VvERF2/VvERF104 at both the protein and DNA levels. Upon ABA signaling perception, VvbZIP60 positively regulates VvERF2/VvERF104, thereby promoting hexose accumulation via VvSWEET14a. Collectively, our findings elucidate the functional role of VvSWEET14a and demonstrate that the VvbZIP60-VvERF2/VvERF104-VvSWEET14a regulatory module is activated by the ABA signaling pathway under water stress. This study provides crucial insights into the molecular mechanisms governing sugar transport under abiotic stress, offering potential applications for grapevine breeding programs.