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Publication Abstract from PubMed

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 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.

Structural analysis of an Avr4 effector ortholog offers insight into chitin-binding and recognition by the Cf-4 receptor.,Kohler AC, Chen LH, Hurlburt N, Salvucci A, Schwessinger B, Fisher AJ, Stergiopoulos I Plant Cell. 2016 Jul 8. pii: tpc.00893.2015. PMID:27401545^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.