Abstract: Tomato with highly significant differences in fruit cracking rate were used as the materials to analyze the expression differences of the SlPL（Solyc03g111690）gene，which was further functionally validated using genetic transformation. The results showed that the expression of SlPL was significantly higher in crack-susceptible tomato‘NT189’than in crack-resistant tomato‘NT91’；in tomato fruit was significantly higher than that in other organs such as roots，stems，leaves and flowers，and the expression was higher in the break ripen and red ripen stages of the fruit. Fruit cracking was further induced by irrigation and ABA treatments，and it was found that the expression of SlPL was overall significantly higher in the fruit of crack-susceptible materials than that of crack-resistant ones in the same treatment period. SlPL overexpression（OEPL）and knockout（pl）lines were then obtained by genetic transformation. OEPL was more susceptible to fruit cracking and had significantly lower fruit firmness and pl had higher fruit firmness than the wild type. OEPL fruit had significantly lower pro-pectin content than the wild type，and significantly higher water-soluble pectin content than the wild type，while pl fruit had significantly higher pro-pectin and total pectin content than the wild type. Pectin cleavage enzyme activity was significantly higher in OEPL fruits than in wild type，and pectin cleavage enzyme activity was significantly lower in pl fruits than in wild type. Gene expression analysis revealed that the relative expression of cell wall metabolism-related genes SlPG2，SlPME2.1，SlCel2，SlGH9C5，and ethylene synthesis pathway-related genes SlACS4 and SlACO1 was significantly higher in OEPL fruits than in wild type，and the opposite was true for pl fruits. pl fruits showed a significantly higher relative expression of the ethylene-responsive factor SlERF2 than in wild type. Observations of the pericarp microstructure revealed that the cells of the epidermal layer and thin-walled cells were more sparsely arranged in OEPL compared with wild type，and those cells were tightly arranged in pl.

Key words: tomato, fruit cracking, SlPL, functional identification