PMID:24654978

Citation	Pel, MJ, Van Dijken, AJ, Bardoel, BW, Seidl, MF, Van der Ent, S, Van Strijp, JA and Pieterse, C' (2014) Pseudomonas syringae evades host immunity by degrading flagellin monomers with alkaline protease AprA. Mol. Plant Microbe Interact. '
Abstract	Bacterial flagellin molecules are strong inducers of innate immune responses in both mammals and plants. The opportunistic pathogen Pseudomonas aeruginosa secretes an alkaline protease called AprA that degrades flagellin monomers. Here, we show that AprA is widespread among a wide variety of bacterial species. In addition we investigated the role of AprA in virulence of the bacterial plant pathogen Pseudomonas syringae pv. tomato DC3000 (Pst). The AprA-deficient Pst ∆aprA knockout mutant was significantly less virulent on both tomato and A. thaliana. Moreover, infiltration of A. thaliana Col-0 leaves with Pst ∆aprA evoked a significantly higher level of expression of the defense-related genes FRK1 and PR-1 than did wild-type Pst. In the flagellin receptor mutant fls2, pathogen virulence and defense-related gene activation did not differ between Pst and Pst ∆aprA. Together, these results suggest that AprA of Pst is important for evasion of recognition by the FLS2 receptor, allowing wild-type Pst to be more virulent on its host plant than AprA-deficient Pst ∆aprA. To provide further evidence for the role of Pst AprA in host immune evasion, we overexpressed the AprA inhibitory peptide AprI of Pst in A. thaliana to counteract the immune evasive capacity of Pst AprA. Ectopic expression of aprI in A. thaliana resulted in an enhanced level of resistance against wild-type Pst, while the already elevated level of resistance against Pst ∆aprA remained unchanged. Together, these results indicate that evasion of host immunity by the alkaline protease AprA is important for full virulence of Pst and likely acts by preventing flagellin monomers from being recognized by its cognate immune receptor.
Links	PubMed Online version:10.1094/MPMI-02-14-0032-R
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
PSESY:S3ML65	enables	GO:0008233: peptidase activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete
PSESY:S3ML65		GO:0008233: peptidase activity	ECO:0000314:		F		Figure 2: When the purified AprA protein was present with flagellin monomers, proteolysis of the flagellin monomers occurred.	complete CACAO 9723
PSESY:S3MID4		GO:0030414: peptidase inhibitor activity	ECO:0000314:		F		Figure 2: When the AprA protein was present with flagellin monomers, proteolysis of the flagellin monomers occurred. When the AprI protein was added to the AprA protein/flagellin monomer mixture, proteolysis of the flagellin monomers did not occur. This is showing that aprI is acting as an inhibitor to the aprA gene.	complete CACAO 9724
PSESY:S3MID4	enables	GO:0030414: peptidase inhibitor activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete

References

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