The chitin-binding Cladosporium fulvum effector protein Avr4 is a virulence factor

H.P. van Esse, M.D. Bolton, I. Stergiopoulos, P.J.G.M. de Wit, B.P.H.J. Thomma

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178 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)1092-1101
JournalMolecular Plant-Microbe Interactions
Issue number9
Publication statusPublished - 2007


  • pathogenesis-related proteins
  • plant antifungal proteins
  • transgenic tomato plants
  • avirulence gene avr9
  • disease resistance
  • arabidopsis-thaliana
  • polyphenol oxidase
  • cf-4-mediated resistance
  • hypersensitive response
  • microbial pathogens


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