The MdLRR-RLK1-MdGRP1-LIKE module improved biotic stress resistance in apple

Apple is an important economic species, but it suffers from biotic stress during its growth and development. Fungi and pests are two types of biotic stress that have significant destructive effects on apple. Members of the leucine-rich repeat receptor-like kinase (LRR-RLK) family play a key role in regulating plant responses to biotic stress. In this study, overexpressing MdLRR-RLK1 enhanced apple resistance to Colletotrichum fructicola and aphids by promoting the expression of resistance genes such as WRKYs, PRs and JA-pathway genes, as well as increasing the content of antioxidant enzymes and secondary metabolites. Additionally, MdLRR-RLK1 could interact with MdGRP1-LIKE in vivo and in vitro, and MdLRR-RLK1 could phosphorylate MdGRP1-LIKE in vitro. Overexpressing MdGRP1-LIKE enhanced apple resistance to C. fructicola by increasing the expression of resistance genes such as WRKYs and PRs and the content of antioxidant enzymes. However, overexpressing MdGRP1-LIKE did not enhance the apple resistance to aphids. These findings reveal the mechanism by which the MdLRR-RLK1-MdGRP1-LIKE module regulates apple resistance to C. fructicola stress.