Involvement of MdWRKY40 in the Defense of Mycorrhizal Apple Against Fusarium Solani

Background: Apple ( Malus domestica Borkh.) is an important economic crop. The pathological effects of Fusarium spp., a group of soilborne pathogens, on the root systems of apple plants was unknown. It was unclear how mycorrhizal apple seedlings resist infection by F. solani . The transcriptional profiles of mycorrhizal and non-mycorrhizal plants infected by F. solani were compared using RNA-Seq. Results: : Infection with F. solani significantly reduced the dry weight of apple roots, and the roots of mycorrhizal apple plants were less damaged when the plants were infected with F. solani . They also had enhanced activity of antioxidant enzymes and a reduction in the oxidation of membrane lipids. A total of 1,839 differentially expressed genes (DEGs) were obtained after mycorrhizal and non-mycorrhizal apple plants were infected with F. solani . A gene ontogeny (GO) analysis showed that most DEGs were involved in the binding of ADP and calcium ions. In addition, the enrichment observed from an analysis with the Kyoto Encyclopedia of Genes and Genomes (KEGG) primarily involved plant-pathogen interaction and Glycolysis/Gluconeogenesis, the mitogen-activated protein kinase (MAPK) signaling pathway, and plant hormone signal transduction. Based on a MapMan analysis, an enormous number of DEGs were involved in the response of mycorrhizal plants to stress. Among them, the overexpressed transcription factor MdWRKY40 significantly improved the resistance of ‘Orin’ to F. solani and the expression of the resistance gene MdGLU by binding the promoter of MdGLU . Conclusion: This paper outlines how the inoculation of apple seedlings by arbuscular mycorrhizal fungi reduces the response to stress at the transcription level of the root system following infection with F. solani , and MdWRKY40 played an important role in the resistance of mycorrhizal apple seedlings to infection with F. solani .