FaSWEET17 negative regulates sucrose accumulation in strawberry fruit

• Potassium sulfate treatment can increase the sucrose content of strawberry fruits. • FaSWEET17 negatively regulates sucrose transport in strawberry fruits. • FaSWEET17 regulates strawberry sucrose content by modulating sugar metabolism genes. In plants, the sugar content in fruit is a key factor in determining flavor quality and market competitiveness. SWEET family sugar transport proteins are involved in transmembrane sugar transport, but their roles in sugar translocation within strawberry fruits remain relatively understudied. Given that potassium fertilization is often reported to regulate fruit sugar metabolism, this study first investigated the effects of potassium sulfate treatment on sugar accumulation in strawberry fruits. It was found that potassium sulfate treatment not only increased the sucrose content in 'Yanli' strawberry fruits, but also down-regulated the expression level of the FaSWEET17 . Spatiotemporal expression analysis revealed that FaSWEET17 expression was highest in floral organs and immature green fruit stages, and was significantly down-regulated during fruit ripening. Subcellular localization assays confirmed that the FaSWEET17 protein is localized to the plasma membrane. Functional validation experiments demonstrated that overexpression of FaSWEET17 significantly reduced sucrose content in the fruits of both 'Yanli' and 'Yuehua' strawberry cultivars. Conversely, silencing this gene markedly promoted sucrose accumulation. RT-qPCR analysis further revealed that genetic manipulation of FaSWEET17 significantly affected the expression of key genes involved in sucrose synthesis and metabolic pathways. In conclusion, this study provides the first evidence that strawberry SWEET17 acts as a negative regulator of fruit sucrose content. It down-regulation represents a vital mechanism promoting sucrose accumulation in fruits, providing novel theoretical foundations and a candidate target for molecular breeding approaches aimed at the targeted regulation of strawberry fruit sugar metabolism and quality improvement.