Autophagy is a highly conserved self-degradation process that involves the degradation and recycling of cellular components and organelles. Although the involvement of autophagy in metabolic changes during fruit ripening has been preliminarily demonstrated, the variations in autophagic flux and specific functional roles in tomato fruit ripening remain to be elucidated. In this study, we analyzed the variations in autophagic flux during tomato fruit ripening. The results revealed differential expression of the SlATG8 family members during tomato fruit ripening. Transmission electron microscopy observations and dansylcadaverine (MDC) staining confirmed the presence of autophagy at the cellular level in tomato fruits. Furthermore, the overexpression of SlATG8f induced the formation of autophagosomes, increased autophagic flux within tomato fruits, and effectively enhanced the expression of ATG8 proteins during the color-transition phase of fruit ripening, thus promoting tomato fruit maturation. SlATG8f overexpression also led to the accumulation of vitamin C (VC) and soluble solids while reducing acidity in the fruit. Collectively, our findings highlight the pivotal role of SlATG8f in enhancing tomato fruit ripening, providing insights into the mechanistic involvement of autophagy in this process. This research contributes to a better understanding of the key factors that regulate tomato fruit quality and offers a theoretical basis for tomato variety improvement.

Caffeic acid O-methyltransferase 1 (COMT1) is a key enzyme that is involved in melatonin synthesis, affecting the melatonin content in plants. In this experiment, tomato plants (slcomt1) with silenced SlCOMT1 gene expression were used to investigate the effects of SlCOMT1 deficiency on fruit growth, development, and quality formation. The results show that the slcomt1 plants exhibited prolonged fruit development, with reductions in the relative expression levels of SlCOMT1 by 71.1%, 79.7%, 83.9%, and 90.6% during the green fruit, breaker, orange ripening, and red ripening stages, respectively. The endogenous melatonin content also decreased by 29.4%, 43%, 45%, and 61.4% in the corresponding stages. Furthermore, the slcomt1 plants showed a decrease in the individual fruit weight, seed number per fruit, and fruit set rate by approximately 51.1%, 48.2%, and 30.4%, respectively. The slcomt1 plants exhibited an increase in the titratable acid content by 32.1%, 22.1%, 10.3%, and 24.4% during the green fruit, breaker, orange ripening, and red ripening stages, while the sugar-to-acid ratio decreased by 44.9%, 32.6%, 22.7%, and 36.8%. The slcomt1 plants also displayed increased fruit firmness, along with reductions in the relative expression levels of the cell wall and carotenoid-related genes and carotenoid content. Specifically, the Vc content in the slcomt1 plants decreased by 80.7% during the green fruit stage, and by 11.5%, 17.1%, and 2.6% during the breaker, orange ripening, and red ripening stages, respectively. The soluble protein content exhibited a decreasing trend in the corresponding stages. This study highlights the important role of endogenous melatonin in fruit physiology and quality formation, providing insights for further research and application of melatonin in agriculture.

Autophagy is a highly conserved self-degradation process involving the degradation and recycling of cellular components and organelles. Although the involvement of autophagy in metabolic changes during fruit ripening has been preliminarily demonstrated, the variations in autophagic flux and specific functional roles in fruit ripening remain to be elucidated. In this study, we analyzed the occurrence of autophagy during tomato fruit ripening. The results revealed differential expression of SlATG8 family member during tomato fruit ripening. Transmission electron microscopy observations and dansylcadaverine (MDC) staining confirmed the presence of autophagy at the cellular level in tomato fruits. Furthermore, the overexpression of SlATG8f induced the formation of autophagosomes, increased autophagic flux within tomato fruits, effectively enhanced the expression of ATG8 proteins during the color transition phase of fruit ripening, thereby promoting tomato fruit maturation. This overexpression also led to the accumulation of vitamin C (VC) and soluble solids while reducing acidity in the fruit. Collectively, our findings highlight the pivotal role of SlATG8f in enhancing tomato fruit ripening, providing insights into the mechanistic involvement of autophagy in this process. This research contributes to a better understanding of key factors regulating tomato fruit quality and offers a theoretical basis for tomato variety improvement.