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Apoplastic effectors secreted by two unrelated eukaryotic plant pathogens target the tomato defense protease Rcr3.

ABSTRACT: Current models of plant-pathogen interactions stipulate that pathogens secrete effector proteins that disable plant defense components known as virulence targets. Occasionally, the perturbations caused by these effectors trigger innate immunity via plant disease resistance proteins as described by the "guard hypothesis." This model is nicely illustrated by the interaction between the fungal plant pathogen Cladosporium fulvum and tomato. C. fulvum secretes a protease inhibitor Avr2 that targets the tomato cysteine protease Rcr3(pim). In plants that carry the resistance protein Cf2, Rcr3(pim) is required for resistance to C. fulvum strains expressing Avr2, thus fulfilling one of the predictions of the guard hypothesis. Another prediction of the guard hypothesis has not yet been tested. Considering that virulence targets are important components of defense, different effectors from unrelated pathogens are expected to evolve to disable the same host target. In this study we confirm this prediction using a different pathogen of tomato, the oomycete Phytophthora infestans that is distantly related to fungi such as C. fulvum. This pathogen secretes an array of protease inhibitors including EPIC1 and EPIC2B that inhibit tomato cysteine proteases. Here we show that, similar to Avr2, EPIC1 and EPIC2B bind and inhibit Rcr3(pim). However, unlike Avr2, EPIC1 and EPIC2B do not trigger hypersensitive cell death or defenses on Cf-2/Rcr3(pim) tomato. We also found that the rcr3-3 mutant of tomato that carries a premature stop codon in the Rcr3 gene exhibits enhanced susceptibility to P. infestans, suggesting a role for Rcr3(pim) in defense. In conclusion, our findings fulfill a key prediction of the guard hypothesis and suggest that the effectors Avr2, EPIC1, and EPIC2B secreted by two unrelated pathogens of tomato target the same defense protease Rcr3(pim). In contrast to C. fulvum, P. infestans appears to have evolved stealthy effectors that carry inhibitory activity without triggering plant innate immunity.

SUBMITTER: Song J

PROVIDER: S-EPMC2635833 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Apoplastic effectors secreted by two unrelated eukaryotic plant pathogens target the tomato defense protease Rcr3.

Song Jing J Win Joe J Tian Miaoying M Schornack Sebastian S Kaschani Farnusch F Ilyas Muhammad M van der Hoorn Renier A L RA Kamoun Sophien S

Proceedings of the National Academy of Sciences of the United States of America 20090126 5

Current models of plant-pathogen interactions stipulate that pathogens secrete effector proteins that disable plant defense components known as virulence targets. Occasionally, the perturbations caused by these effectors trigger innate immunity via plant disease resistance proteins as described by the "guard hypothesis." This model is nicely illustrated by the interaction between the fungal plant pathogen Cladosporium fulvum and tomato. C. fulvum secretes a protease inhibitor Avr2 that targets t ...[more]

PMID: 19171904

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Project description:Our interest lies in how plants respond to bacterial pathogens. Over the past three years we have identified and documented reproducible, landmark biochemical and molecular events following the challenge of Arabidopsis with the phytopathogenic enterobacteria P. syringae. Significantly, our studies revealed 60% of cDNA-AFLP differentials not present on the 8,200 feature GeneChips and 20% absent from public EST databases (de Torres in press). We now seek to exploit this background using carefully defined time-points to analyse global changes in the Arabidopsis transcriptome using challenges selected to define gene targets implicated in (i) expression of basal immunity (ii) the establishment of successful parasitism (resistance) by a virulent pathogen (host). The results will provide a rationale for future functional assays of the identified pathways using transgenic knockouts and mutant analyses. Additionally, data will provide underpinning support for comparative proteomics of the defense response currently in progress with GARNet support using the same experimental parameters (BBSRC 32/P14635). We propose the following treatments: (i) Mock vs. DC3000hrpA @ 60 min: 60 minutes is subsequent to host immediate-early stress responses and will catalogue the innate responses induced by pathogen associated molecular patterns. The hrpA lesion will ensure no type III effectors influence transcriptional responses. Gene products induced at this time are predicted to potentiate latter host responses (2 treatments X 3 biological replicates = 6 chips). (ii) Mock vs. DC3000 vs. DC3000hrpA vs. DC3000::avrRpm1 @ 4 hours: A key time point previously defined where no macroscopic symptoms are visible but significant differences exist between compatible and incompatible interactions at the molecular and physiological levels. These treatments will serve to define the earliest genes induced by the complement of DC3000 type III effector and will specifically define genes/pathways suppressed by virulence factors in addition to those implicated in orchestration of the hypersensitive cell death. We will also include an incompatible interaction on a transgenic line expressing an RPM1 interacting protein, which fails to mount an HR but exhibits hyper-resistance. We predict this challenge will separate the resistance response (pathogen restriction) from that associated with hypersensitive cell death (5 treatments X 3 biological replicates = 15 chips). (iii) Mock vs. DC3000 vs. DC3000hrpA @ 14 hours: At 10 h before phenotypes are apparent in the DC3000 background, Type III effector delivery is well advanced and impact on host transcription maximal (3 treatments X 3 biological replicates = 9 chips). Keywords: time_series_design; pathogenicity_design; compound_treatment_design

Dataset Information

Apoplastic effectors secreted by two unrelated eukaryotic plant pathogens target the tomato defense protease Rcr3.

Publications

Apoplastic effectors secreted by two unrelated eukaryotic plant pathogens target the tomato defense protease Rcr3.

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