title: The major specificity-determining amino acids of the tomato Cf-9 disease resistance protein are at hypervariable solvent-exposed positions in the central leucine-rich repeats.
abstract: The interaction between tomato and the leaf mold pathogen Cladosporium fulvum is controlled in a gene-for-gene manner by plant Cf genes that encode membrane-anchored extracytoplasmic leucine-rich repeat (LRR) glycoproteins, which confer recognition of their cognate fungal avirulence (Avr) proteins. Cf-9 and Cf-4 are two such proteins that are 91% identical yet recognize the sequence-unrelated fungal avirulence determinants Avr9 and Avr4, respectively. As shown previously, Cf-4 specificity is determined by three putative solvent-exposed residues in the central LRR and a deletion of two LRR relative to Cf-9. In this study, we focused on identifying the specificity determinants of Cf-9. We generated chimeras between Cf-9 and its close homologue Cf-9B and identified five amino acid residues that constitute major specificity determinants of Cf-9. Introduction of these residues into Cf-9B allowed recognition of Avr9. Consistent with a role in recognition specificity, the identified residues are putatively solvent exposed in the central LRR and occupy hypervariable positions in the global Cf alignment. One of the specificity residues is not found in any other known Cf protein, suggesting the importance of diversifying selection rather than sequence exchange between homologues. Interestingly, there is an overlap between the Cf-4 and Cf-9 specificity-determining residues, precluding a protein with dual specificity.
authors.affiliation: The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK.
authors.forename: Brande B H
authors.initials: BB
authors.lastname: Wulff
authors.forename: Antje
authors.initials: A
authors.lastname: Heese
authors.forename: Laurence
authors.initials: L
authors.lastname: Tomlinson-Buhot
authors.forename: David A
authors.initials: DA
authors.lastname: Jones
authors.forename: Marcos
authors.initials: M
authors.lastname: de la Peña
authors.forename: Jonathan D G
authors.initials: JD
authors.lastname: Jones
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D002963:Cladosporium / Q000472:pathogenicity*; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology; D017343:Genes, Plant; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000502:physiology; D000090263:Leucine-Rich Repeat Proteins; D018551:Solanum lycopersicum / Q000235:genetics* / Q000382:microbiology* / Q000502:physiology; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012997:Solvents
chemical_list: D000596:Amino Acids; C109609:Cf protein, Lycopersicon esculentum; D005656:Fungal Proteins; D000090263:Leucine-Rich Repeat Proteins; D008562:Membrane Glycoproteins; D010940:Plant Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D012997:Solvents; C073605:AVR9 protein, Cladosporium fulvum