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PLoS Pathog. 2016 Sep 7;12(9):e1005874. doi: 10.1371/journal.ppat.1005874. eCollection 2016 Sep.

Screen of Non-annotated Small Secreted Proteins of Pseudomonas syringae Reveals a Virulence Factor That Inhibits Tomato Immune Proteases.

Author information

1
Plant Chemetics lab, Max Planck Institute for Plant Breeding Research, Cologne, Germany.
2
Center for Plant Science Innovation and the Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
3
Department of Plant Biology, University of Szeged, Szeged, Hungary.
4
Plant Chemetics lab, Department of Plant Sciences, University of Oxford, Oxford, United Kingdom.
5
Mass Spectrometry Group, Max Planck Institute for Plant Breeding Research, Cologne, Germany.

Abstract

Pseudomonas syringae pv. tomato DC3000 (PtoDC3000) is an extracellular model plant pathogen, yet its potential to produce secreted effectors that manipulate the apoplast has been under investigated. Here we identified 131 candidate small, secreted, non-annotated proteins from the PtoDC3000 genome, most of which are common to Pseudomonas species and potentially expressed during apoplastic colonization. We produced 43 of these proteins through a custom-made gateway-compatible expression system for extracellular bacterial proteins, and screened them for their ability to inhibit the secreted immune protease C14 of tomato using competitive activity-based protein profiling. This screen revealed C14-inhibiting protein-1 (Cip1), which contains motifs of the chagasin-like protease inhibitors. Cip1 mutants are less virulent on tomato, demonstrating the importance of this effector in apoplastic immunity. Cip1 also inhibits immune protease Pip1, which is known to suppress PtoDC3000 infection, but has a lower affinity for its close homolog Rcr3, explaining why this protein is not recognized in tomato plants carrying the Cf-2 resistance gene, which uses Rcr3 as a co-receptor to detect pathogen-derived protease inhibitors. Thus, this approach uncovered a protease inhibitor of P. syringae, indicating that also P. syringae secretes effectors that selectively target apoplastic host proteases of tomato, similar to tomato pathogenic fungi, oomycetes and nematodes.

PMID:
27603016
PMCID:
PMC5014320
DOI:
10.1371/journal.ppat.1005874
[Indexed for MEDLINE]
Free PMC Article

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