SlPPDK modulates sugar and acid metabolism to influence flavor quality during tomato fruit ripening

Fruit ripening is a highly intricate process, where the dynamic interplay of soluble sugar and organic acid metabolism is crucial for developing the characteristic flavor qualities. Pyruvate orthophosphate dikinase (PPDK) plays a pivotal role in modulating the process of gluconeogenesis during plant development. However, the specific physiological role of PPDK in fruit development has yet to be elucidated. In this study, we investigated the expression pattern, subcellular localization and functional significance of SlPPDK in tomato fruits. Our results reveal that SlPPDK is highly expressed in fruits and flowers, with its expression progressively increasing as the fruit ripens. Subcellular localization analyses demonstrate that SlPPDK is distributed in the cell membrane, cytoplasm, and nucleus. Using CRISPR/Cas9 technology, we generated SlPPDK knockout mutants, which exhibited a marked reduction in enzyme activity, leading to significant alterations in sugar and organic acid metabolism. These findings highlight the critical role of SlPPDK in maintaining the sugar-acid balance essential for tomato flavor quality and provide a foundation for future breeding strategies aimed at enhancing tomato fruit flavor.