Impact of 4-CPA floral dipping on tomato fruit quality and functional study of the SlTCP16-SlEG24-D-glucose module

4-Chlorophenoxyacetic acid (4-CPA) floral dipping is a prevalent agronomic strategy to enhance fruit set and yield, yet its molecular impacts on fruit quality traits remain elusive. In this study, we show that 4-CPA treatment not only improved fruit set rate, fruit size, lycopene, flavonoid accumulation and antioxidant capacity but also decreased soluble sugar and gamma-aminobutyric acid (GABA) levels in tomato fruits relative to control group. Integrative transcriptome and metabolome profiling revealed that the starch and sucrose metabolism pathway is a target of 4-CPA regulation, with the SlTCP16-SlEG24 -D-glucose regulatory module playing a role in mediating 4-CPA responses. Functional validation demonstrated that SlTCP16 overexpression mitigates the 4-CPA-induced loss of D-glucose content in mature fruits. These findings uncover a molecular mechanism underlying 4-CPA-mediated fruit quality regulation and provide a critical genetic module for the improvement of tomato varieties under 4-CPA cultivation systems.