Autophagy-regulated ethylene synthesis mediates fruit ripening by affecting the accumulation of lycopene, sugars and organic acids in tomato

Autophagy is a universal cellular process in eukaryotes that plays a critical role in plant growth and stress response. However, the role of autophagy in fruit ripening is largely unknown. Here, we demonstrated that most autophagy-related genes (ATGs) were up-regulated during tomato (Solanum lycopersicum L.) fruit ripening. By using mutants of different autophagy pathway genes (ATG6, ATG10, ATG18a), we revealed that the deficiency of autophagy delayed the ripening of fruit. Compared with wild-type (WT), the production of ethylene was significantly reduced and the accumulation of lycopene was delayed in atg mutants during fruit ripening. We also observed the contents of glucose and fructose were both significantly decreased in atg mutants compared with WT, while the content of organic acids showed the opposite trend. Additionally, the negative regulator of ethylene production, APETALA2a (AP2a), interacted with ATG8 through a specific ATG8-interacting motif (AIM) and could be degraded through the autophagy pathway. These results demonstrate that autophagy plays a critical role in fruit ripening by regulating ethylene production and the accumulation of pigments, sugars and organic acids in tomato.