Tonoplast sugar transporters coordinately regulate tomato fruit development and quality

Fruit yield and quality are antagonistically regulated traits in tomato. An excessive focus on increasing yield often leads to a decline in quality. Achieving a delicate balance between high yield and desirable fruit quality is a challenging aspect of tomato breeding. In this study, we discovered that disrupting the function of the tomato tonoplast sugar transporter 3a (TST3a) significantly enhances both fruit weight and flavor. Three TSTs have been identified in tomato, namely SlTST1, SlTST3a, and SlTST3b; they possess the same sugar transport specificity for fructose and glucose and redundantly control cell expansion during fruit development. Sugar accumulation in sltst mutants correlates significantly with fruit size and flavor. The enlarged fruits in sltst3a mutants result from sugar accumulation due to the increased abundance of SlTST1 at the tonoplast coupled with the highest sugar transport capacity of SlTST1 among the three SlTSTs. Further experiments established that SlTST3a prevents the localization of SlTST1 to the tonoplast by inhibiting its interaction with VH1-interacting kinase (SlVIK). Mutation of SlTST3a in cultivated tomato can enhance both tomato fruit size and sugar content. Our findings offer potential avenues for simultaneously improving fruit quality and yield, providing valuable insights into the mechanisms underlying sugar storage during fruit development.