Quantitative proteomic sequencing of hybrid populations reveals the function of sorbitol in apple resistance to .

Apple ring rot, which is caused by , is one of the most devastating diseases of apple. However, the lack of a known molecular resistance mechanism limits the development of resistance breeding. Here, the 'Golden Delicious' and 'Fuji Nagafu No. 2' apple cultivars were crossed, and a population of 194 individuals was generated. The hybrids were divided into five categories according to their differences in resistance during three consecutive years. Quantitative proteomic sequencing was performed to analyze the molecular mechanism of the apple response to infection. Hierarchical clustering and weighted gene coexpression network analysis revealed that photosynthesis was significantly correlated with the resistance of apple to . The level of chlorophyll fluorescence in apple functional leaves increased progressively as the level of disease resistance improved. However, the content of soluble sugar decreased with the improvement of disease resistance. Further research revealed that sorbitol, the primary photosynthetic product, played major roles in apple resistance to . Increasing the content of sorbitol by overexpressing dramatically enhanced resistance of apple calli to by activating the expression of salicylic acid signaling pathway-related genes. However, decreasing the content of sorbitol by silencing showed the opposite phenotype. Furthermore, exogenous sorbitol treatment partially restored the resistance of -RNAi lines to . Taken together, these findings reveal that sorbitol is an important metabolite that regulates the resistance of apple to and offer new insights into the mechanism of plant resistance to pathogens.