title: Cladosporium fulvum Avr4 protects fungal cell walls against hydrolysis by plant chitinases accumulating during infection.
abstract: Resistance against the leaf mold fungus Cladosporium fulvum is mediated by the tomato Cf proteins which belong to the class of receptor-like proteins and indirectly recognize extracellular avirulence proteins (Avrs) of the fungus. Apart from triggering disease resistance, Avrs are believed to play a role in pathogenicity or virulence of C. fulvum. Here, we report on the avirulence protein Avr4, which is a chitin-binding lectin containing an invertebrate chitin-binding domain (CBM14). This domain is found in many eukaryotes, but has not yet been described in fungal or plant genomes. We found that interaction of Avr4 with chitin is specific, because it does not interact with other cell wall polysaccharides. Avr4 binds to chitin oligomers with a minimal length of three N-acetyl glucosamine residues. In vitro, Avr4 protects chitin against hydrolysis by plant chitinases. Avr4 also binds to chitin in cell walls of the fungi Trichoderma viride and Fusarium solani f. sp. phaseoli and protects these fungi against normally deleterious concentrations of plant chitinases. In situ fluorescence studies showed that Avr4 also binds to cell walls of C. fulvum during infection of tomato, where it most likely protects the fungus against tomato chitinases, suggesting that Avr4 is a counter-defensive virulence factor.
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, NL-6703 HA Wageningen, The Netherlands.
authors.forename: Harrold A
authors.initials: HA
authors.lastname: van den Burg
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Harrison
authors.forename: Matthieu H A J
authors.initials: MH
authors.lastname: Joosten
authors.forename: Jacques
authors.initials: J
authors.lastname: Vervoort
authors.forename: Pierre J G M
authors.initials: PJ
authors.lastname: de Wit
mesh_terms: D000595:Amino Acid Sequence; D002473:Cell Wall / Q000378:metabolism*; D002686:Chitin / Q000378:metabolism; D002688:Chitinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002963:Cladosporium / Q000378:metabolism / Q000472:pathogenicity* / Q000648:ultrastructure; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D005670:Fusarium / Q000378:metabolism / Q000648:ultrastructure; D006868:Hydrolysis; D025301:Hyphae / Q000378:metabolism; D018551:Solanum lycopersicum / Q000382:microbiology; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D010940:Plant Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014242:Trichoderma / Q000378:metabolism / Q000648:ultrastructure; D037521:Virulence Factors / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*
chemical_list: C085987:AVR4 protein, Cladosporium fulvum; D005656:Fungal Proteins; D010940:Plant Proteins; D037521:Virulence Factors; D002686:Chitin; D002688:Chitinases