title: The AVR4 elicitor protein of Cladosporium fulvum binds to fungal components with high affinity.
abstract: The interaction between tomato and the fungal pathogen Cladosporium fulvum complies with the gene-for-gene system. Strains of C. fulvum that produce race-specific elicitor AVR4 induce a hypersensitive response, leading to resistance, in tomato plants that carry the Cf-4 resistance gene. The mechanism of AVR4 perception was examined by performing binding studies with 125I-AVR4 on microsomal membranes of tomato plants. We identified an AVR4 high-affinity binding site (KD = 0.05 nM) which exhibited all the characteristics expected for ligand-receptor interactions, such as saturability, reversibility, and specificity. Surprisingly, the AVR4 high-affinity binding site appeared to originate from fungi present on infected tomato plants rather than from the tomato plants themselves. Detailed analysis showed that this fungus-derived, AVR4-specific binding site is heat- and proteinase K-resistant. Affinity crosslinking demonstrated that AVR4 specifically binds to a component of approximately 75 kDa that is of fungal origin. Our data suggest that binding of AVR4 to a fungal component or components is related to the intrinsic virulence function of AVR4 for C. fulvum.
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Binnenhaven 5, 6709 PD Wageningen, The Netherlands.
authors.forename: Nienke
authors.initials: N
authors.lastname: Westerink
authors.forename: Ronelle
authors.initials: R
authors.lastname: Roth
authors.forename: Harrold A
authors.initials: HA
authors.lastname: Van den Burg
authors.forename: Pierre J G M
authors.initials: PJ
authors.lastname: De Wit
authors.forename: Matthieu H A J
authors.initials: MH
authors.lastname: Joosten
mesh_terms: D001667:Binding, Competitive; D002963:Cladosporium / Q000254:growth & development* / Q000378:metabolism; D056229:Fungal Structures / Q000378:metabolism*; D007457:Iodine Radioisotopes; D018551:Solanum lycopersicum / Q000382:microbiology*; D008861:Microsomes / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D013045:Species Specificity
chemical_list: D007457:Iodine Radioisotopes; D010100:Oxygen