title: The chitin-binding Cladosporium fulvum effector protein Avr4 is a virulence factor.
abstract: The biotrophic fungal pathogen Cladosporium fulvum (syn. Passalora fulva) is the causal agent of tomato leaf mold. The Avr4 protein belongs to a set of effectors that is secreted by C. fulvum during infection and is thought to play a role in pathogen virulence. Previous studies have shown that Avr4 binds to chitin present in fungal cell walls and that, through this binding, Avr4 can protect these cell walls against hydrolysis by plant chitinases. In this study, we demonstrate that Avr4 expression in Arabidopsis results in increased virulence of several fungal pathogens with exposed chitin in their cell walls, whereas the virulence of a bacterium and an oomycete remained unaltered. Heterologous expression of Avr4 in tomato increased the virulence of Fusarium oxysporum f. sp. lycopersici. Through tomato GeneChip analyses, we demonstrate that Avr4 expression in tomato results in the induced expression of only a few genes. Finally, we demonstrate that silencing of the Avr4 gene in C. fulvum decreases its virulence on tomato. This is the first report on the intrinsic function of a fungal avirulence protein that has a counter-defensive activity required for full virulence of the pathogen.
authors.affiliation: Laboratory of Phytopathology, Centre for Biosystems Genomics (CBSG), Wageningen University, Binnenhaven 5, 6709 PD Wageningen, The Netherlands.
authors.forename: H Peter
authors.initials: HP
authors.lastname: van Esse
authors.forename: Melvin D
authors.initials: MD
authors.lastname: Bolton
authors.forename: Ioannis
authors.initials: I
authors.lastname: Stergiopoulos
authors.forename: Pierre J G M
authors.initials: PJ
authors.lastname: de Wit
authors.forename: Bart P H J
authors.initials: BP
authors.lastname: Thomma
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D002686:Chitin / Q000378:metabolism*; D002963:Cladosporium / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005670:Fusarium / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D011485:Protein Binding; D014158:Transcription, Genetic; D037521:Virulence Factors
chemical_list: C085987:AVR4 protein, Cladosporium fulvum; D005656:Fungal Proteins; D037521:Virulence Factors; D002686:Chitin