Nitric oxide delayed tomato fruit coloring by regulating chlorophyll- and carotenoid-related genes in a SlSPL6c-dependent manner

Nitric oxide (NO) and the SQUAMOSA Promoter Binding Protein-Like family both have been shown to be involved in the fruit ripening process. This study explored the function of SlSPL6c gene in tomato (Solanum lycopersicum) fruit color change, as well as its involvement in NO-regulated coloring. The NO donor S-nitrosoglutathione (GSNO) delayed tomato fruit coloring by increasing SlSPL6c expression. The silencing of SlSPL6c accelerated tomato fruit color change, whereas overexpression of the gene delayed fruit coloring. In the SlSPL6c-silenced fruits, GSNO did not exert a significant influence on chlorophyll and carotenoid level. Whereas the chlorophyll level was significantly upregulated and carotenoid level was downregulated by GSNO in the SlSPL6c overexpression fruits. Moreover, GSNO significantly downregulated the relative expression level of the chlorophyll degradation genes (SGR1, RCCR) and carotenoid synthesis genes (PSY1) in both WT and SlSPL6c overexpression fruits; however, it did not affect the expression level of these genes in SlSPL6c silenced fruits. Thus, NO might delay tomato fruit coloring by downregulating chlorophyll degradation and carotenoid synthesis gene expression in a manner dependent on SlSPL6c. The insights gained from this study may have practical implications for the development of strategies to extend fruit shelf life in tomato and other fruit crops.