Activation of small heat shock protein (SlHSP17.7) gene by cell wall invertase inhibitor (SlCIF1) gene involved in sugar metabolism in tomato

Fruit quality formation involves a series of physiological and biochemical changes during fruit ripening. Sucrose metabolism plays not only important roles in fruit ripening to establish energy status and nutritional quality but also a non-nutritive role in gene expression. In carbon metabolism and fruit ripening, cell wall invertases (CWINs) perform essential regulatory functions. Knowledge regarding the gene expression changes that occur following the repression of CWIN activity in fruit through the overexpression of a cell-wall inhibitor of β-fructosidase (CIF) under a fruit-specific promoter is limited. To further explore the molecular mechanism of sucrose regulation, global expression profiling of the fruits of transgenic tomato (Solanum lycopersicum) plants carrying a cell wall invertase inhibitor (SlCIF1) gene was performed using a microarray. In total, 622 and 833 differentially expressed genes (DEGs) were identified. The expression of the SlHSP17.7 gene was increased by thousands of times in the transgenic-SlCIF1 tomato. Then, SlHSP17.7-RNA interference (RNAi) lines were generated by introducing pB7GWIWG2 (I)-SlHSP17.7 into wild-type chmielewskii tomatoes (WT). The sucrose and fructose contents significantly decreased in the RNAi fruits compared with those in the WT. Furthermore, 14 sugar metabolism related genes were also decreased synergistically by silencing SlHSP17.7 gene. Our data indicate that the posttranslational modulation of CWIN activity by SlCIF1 contributes to earlier bloom times. SlHSP17.7 and sugar can interact to regulate the development of tomato fruit and affect the quality of tomato, providing a different insight into improving the quality of tomato.