Cell Wall Invertase Inhibitor SlINVINH1 Acts as a Negative Regulator in Fruit Ripening of Tomato

Sugar metabolism is an important factor in influencing fruit ripening, while the associated mechanism is not well understood. Cell wall invertase (CWIN) inhibitors play important roles in plant organ (such as fruit, seed, leave, tuber) development and stress resistance, as they are able to regulate CWIN activity through protein-protein interaction, affecting sugar levels in plants. Here, we report a novel role of one tomato CWIN inhibitor in regulating fruit ripening. Specifically, knockout of SlINVINH1 gene via CRISPR/Cas9 technique accelerated the onset of fruit ripening process, along with the increase in CWIN activity and contents of sucrose, glucose, fructose and carotenoid and decrease in chlorophyll content in ripening fruits of the CR-slinvinh1 mutants. Transcriptome analysis demonstrated that the differentially expressed genes (DEGs) in fruits of CR-slinvinh1 were enriched in several biological pathways related to fruit ripening and/or sugar metabolism. The expression levels of invertase genes and inhibitor genes in CR-slinvinh1 were consistent with the alterations of invertase activity and sugar levels. Moreover, the transcript levels of a set of pivotal ripening-related marker genes including the global ripening regulator gene SlRIN were increased in ripening fruits of CR-slinvinh1. This study provides novel insights into the regulatory network underlying tomato fruit ripening, as well as a new genetic strategy using CWIN inhibitor genes to simultaneously accelerate fruit ripening and increase fruit sweetness.