Gibberellin Promotes Sugar Accumulation in Longan Fruit via Upregulation of the Plasma Membrane Sugar Transporter DlSWEET3a

Exogenous gibberellin (GA3) significantly improves sugar accumulation in longan (Dimocarpus longan) fruit, yet its molecular mechanism remains unclear. This study demonstrates that 50 mg/L GA3 optimally enhances sucrose, glucose, fructose, total sugar, and sweetness in longan. Transcriptomic analysis revealed 1345 differentially expressed genes (DEGs), including the sugar transporter gene DlSWEET3a, which was upregulated by GA3. Subcellular localization confirmed DlSWEET3a resides on the plasma membrane. Functional assays in yeast demonstrated its ability to transport glucose, fructose, mannose, and galactose. Critically, transient overexpression of DlSWEET3a in longan fruit and stable overexpression in tobacco leaves significantly increased soluble sugar content. These results establish that GA3 promotes sugar accumulation in longan fruit partly through the upregulation of the plasma membrane hexose transporter DlSWEET3a, providing a mechanistic insight into gibberellin-mediated fruit quality improvement.