MdWRKY74 is involved in resistance response to apple replant disease

Apple replant disease (ARD) is a common problem, which occurs in all major apple-growing regions worldwide. It hinders the growth of apple trees and reduces apple yield and quality. Besides, ARD has substantially impeded the development of the apple industry. Fusarium solani, a soil-borne pathogen, is the causative agent of ARD. WRKY transcription factors (TFs) play a crucial role in plant response to biological stress; however, the functional role of apple WRKY-TFs in ARD remains unknown. In this study, F. solani infection apple rootstock ‘M9T337’ induced MdWRKY74 expression was observed. As per the significance analysis, MdWRKY74 expression was positively correlated to endochitinase activity. The MdWRKY74 overexpression in apple callus can significantly improve the resistance to F. solani. In F. solani infection, the relative expression levels of the endochitinase gene (MdECHT) and the activity of endochitinase in the OE-MdWRKY74 calli were higher than those in the control calli. Yeast one-hybrid and electrophoretic mobility transfer analysis revealed the interaction between MdWRKY74 and MdECHT promoter. As per the luciferase reporter analysis, MdWRKY74 significantly increased the activity of the MdECHT promoter. In conclusion, MdWRKY74 was found to be a positive regulator of disease resistance, which improved the apple plant resistance to F. solani infection. This study provides a scientific basis for disease resistance breeding for apple rootstocks.