Journal
PLANT CELL
Volume 28, Issue 8, Pages 1945-1965Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1105/tpc.15.00893
Keywords
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Funding
- Research Investments in Science and Engineering (RISE) program of UC Davis [RI-091]
- Human Frontier Science Program long-term postdoctoral fellowship [LT000674/2012]
- NIH training grant [T32 GM007377]
- U.S. DOE [DE-AC02-76SF00515]
- DOE-BER
- NIH, NIGMS [P41GM103393]
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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.
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