Functional Study And Interaction Target Identification Of An Effector Protein VmPxE1 From Valsa Mali

Valsa mali is a necrotrophic fungus and causes Valsa canker on apple trees,resulting in substantial yield losses in China every year.To date,the key virulence factors of V.mali remain obscure.Studying the pathogenic mechanism of Valsa mali at the molecular level will provide a theoretical basis for further understanding of the disease.Effector proteins are important for fungal pathogenicity.Based on genome sequence of V.mali,we identified an effector gene VmPxE1 from 32 effector genes which could suppressed the Bax-induced cell death in Nicotiana benthamiana.The main experimental results are as follows:1.Identification and functional analysis of VmPxE1By using the yeast secretory system,VmPxE1 was proven to contain a signal peptide with secretory functions.VmPxE1 can suppress BCL-2-associated X protein(BAX)-induced cell death in Nicotiana benthamiana.The expression of VmPxE1 was upregulated during the early infection stage and deletion of VmPxE1 led to significant reductions in virulence on both apple twigs and leaves.After verification of complement,pathogenicity of mutant were similar to wild type 03-8,further proofing the defects of pathogenicity of the deletion mutant caused by VmPxE1 knockout.2.Identification of apple targets of VmPxE1VmPxE1 was shown to target an apple ascorbate peroxidase(MdAPX1)by the yeast two-hybrid screening,bimolecular fluorescence complementation and in vivo coimmunoprecipitation.Sequence phylogenetic analysis suggested that MdAPX1 was an ascorbate peroxidaseIn this study,we identified VmPxE1 as a cell death suppressor,contributing to the full virulence of V.mali and directly targeting a peroxidase of apple trees.This provided insight into the study of the interaction between its host and Valsa mali.Moreover,this research will provide another theoretical foundation for the analysis of the pathogenic mechanism in the future.