A Roadmap for Breeding Sweet Tomatoes

ABSTRACT Sweetness is the most important determinant of the overall desirability of tomato ( Solanum lycopersicum ) fruits. In cultivated tomatoes, sweetness is mainly determined by the contents of fructose and glucose, which are the major carbohydrates in the fruits. In recent years, many key regulators of sugar accumulation in tomato fruit, including sugar metabolism enzymes, sugar transporters, transcription factors, and protein kinases, have been identified through map‐based cloning, genome‐wide association studies, and reverse genetics. A growing number of studies have also indicated that aromatic volatiles, such as apocarotenoid‐ and phenylalanine‐derived volatiles (PHEVs), can improve tomato sweetness independently of sugar content. In this perspective, we summarise recent advances in our understanding of sugar metabolism in tomatoes and discuss progress in identifying aromatic substances that can affect tomato sweetness. We also discuss challenges in increasing tomato sweetness and propose new breeding strategies to further improve sugar content and sweetness in tomatoes.