SlMYBR5 shows preliminary evidence as a negative regulator of tomato fruit ripening by modulating metabolic pathways

Fruit ripening in tomato (Solanum lycopersicum L.) is a complex, genetically regulated process that determines final fruit quality. Through transcriptomic profiling of three ripening stages-green-ripening (GR), breaker (BR), and red-ripening (RR)-we identified an RR-upregulated MYB transcription factor, SlMYBR5. Functional studies demonstrated that SlMYBR5 knockout accelerates ripening, while its overexpression delays it. RNA-seq analysis revealed that differentially expressed genes (DEGs) in the slmybr5 mutant were primarily associated with enzyme activity, secondary metabolism, and carbohydrate metabolism. In contrast, DEGs in the SlMYBR5-OE line were enriched in amino acid metabolism and photosynthesis. Further phenotypic analysis showed that slmybr5 mutants exhibited higher chlorophyll content at the GR stage and accumulated the highest carotenoid levels at the RR stage, whereas SlMYBR5-OE lines displayed reduced pigmentation. Moreover, overexpression of SlMYBR5 led to significant reductions in fruit length and width, although fruit weight was not significantly affected. Collectively, our findings preliminarily establish SlMYBR5 as a key regulator of tomato fruit ripening, acting through the modulation of metabolic pathways, pigmentation, and fruit morphology, thereby revealing a novel layer of metabolic control in the ripening regulatory network.