Biochemical, structural, and functional characterization of the Avr4 core effector family in fungi.
L. CHEN (1), A. Kohler (2), A. Salvucci (3), N. Hurlburt (4), B. Schwessinger (3), A. Fisher (5), I. Stergiopoulos (3) (1) Department of Plant Pathology, UC Davis, U.S.A.; (2) Joint BioEnergy Institute (DOE), U.S.A.; (3) Department of Plant Pathology, UC Davis, U.S.A.; (4) Department of Chemistry, UC Davis, U.S.A.; (5) Department of Molecular and Cellular Biology, UC Davis, U.S.A.

Effectors are secreted microbial proteins that facilitate infections. Research in our lab and elsewhere has revealed the presence of abundant homologous “core” effectors across different fungal species. One such core effector with homologs in many species of Dothideomycete is Avr4, a secreted chitin-binding effector with a conserved CBM14 (carbohydrate-binding module family 14) domain. Despite their low sequence homology, Avr4 effectors have a similar biological function in protecting fungal cell wall chitin against chitinases, and remarkably most are recognized by the cognate Cf-4 immune receptor from tomato. To identify how Cf-4 can perceive so diverse in sequence Avr4 effectors, we have solved the X-ray crystal structure of PfAvr4 from the tomato pathogen Pseudocercospora fuligena and used site-directed mutagenesis to identify the molecular determinants necessary for ligand-binding and recognition in PfAvr4. Our analysis indicated that individual chitin-binding residues do not have a direct effect on the PfAvr4-Cf4 interaction but instead recognition likely stems from the combined effect of multiple residues that define local tertiary folds of Avr4. We also discovered that several Dothideomycetes carry a paralog of Avr4 that we refer to as Avr4-2. Like Avr4, Avr4-2 proteins are small cysteine-rich secreted proteins with a CBM14. The function Avr4-2 is unknown but several lines of evidence suggest that it has fully or partially functionally diversified as compared to Avr4.

Abstract Number: P6-137
Session Type: Poster