Structural analysis of an Avr4 effector ortholog offers insight into chitin binding and recognition by the Cf-4 receptor

Amanda C. Kohler, Li Hung Chen, Nicholas Hurlburt, Anthony Salvucci, Benjamin Schwessinger, Andrew J Fisher, Ioannis Stergiopoulos

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Chitin is a key component of fungal cell walls and a potent inducer of innate immune responses. Consequently, fungi may secrete chitin-binding lectins, such as the Cf-Avr4 effector protein from the tomato pathogen Cladosporium fulvum, to shield chitin from host-derived chitinases during infection. Homologs of Cf-Avr4 are found throughout Dothideomycetes, and despite their modest primary sequence identity, many are perceived by the cognate tomato immune receptor Cf-4. Here, we determined the x-ray crystal structure of Pf-Avr4 from the tomato pathogen Pseudocercospora fuligena, thus providing a three-dimensional model of an Avr4 effector protein. In addition, we explored structural, biochemical, and functional aspects of Pf-Avr4 and Cf-Avr4 to further define the biology of core effector proteins and outline a conceptual framework for their pleiotropic recognition by single immune receptors. We show that Cf-Avr4 and Pf-Avr4 share functional specificity in binding (GlcNAc)6 and in providing protection against plant- and microbial-derived chitinases, suggesting a broader role beyond deregulation of host immunity. Furthermore, structure-guided site-directed mutagenesis indicated that residues in Pf-Avr4 important for binding chitin do not directly influence recognition by Cf-4 and further suggested that the property of recognition is structurally separated or does not fully overlap with the virulence function of the effector.

Original languageEnglish (US)
Pages (from-to)1945-1965
Number of pages21
JournalPlant Cell
Volume28
Issue number8
DOIs
StatePublished - Aug 1 2016

ASJC Scopus subject areas

  • Plant Science
  • Cell Biology

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