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Title: Toward the understanding of TIR-NB-LRR-mediated immunity : study of the AvrRps4 recognition model in Arabidopsis
Author: Saucet, Simon
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2013
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Abstract:
The recognition of pathogen–secreted effectors is a major component of plant innate immunity and is mainly mediated by NB-LRR resistance (R) proteins. However, the mechanisms by which NB-LRR proteins recognize effectors and induce downstream signaling events are poorly known. This PhD work focused on the characterization of TIR-NB-LRR–mediated immnunity in plants. In Arabidopsis, two TIR-NB-LRR encoding R genes, RRS1 and RPS4, are in a head-to-head arrangement on chromosome 5. They interact to confer recognition to AvrRps4 and (with the right allele of RRS1) PopP2, two bacterial effectors, from Pseudomonas syringae and Ralstonia solanacearum respectively. To dissect AvrRps4–triggered immunity, I focused on the RRS1– and RPS4–independent AvrRps4 recognition (RRIR) observed in the Ws-2 and Col-0 Arabidopsis accessions. I map-based cloned another pair of R genes, RRS1B and RPS4B, genetically linked and highly similar to RRS1-RPS4, responsible for the RRIR. Interestingly, RRS1B-RPS4B recognizes AvrRps4 but not PopP2. Using domain swap experiments, I demonstrated that RRS1 exons 5, 6 and 7 specify PopP2 recognition. My data suggest that AvrRps4 and PopP2 interact directly with RRS1 and RRS1B. However, the exact mechanism by which these effectors activate TIR-NB-LRR R proteins remains to be determined. Overexpressing the N-terminal domain of RPS4, RPS4TIR+80, activates cell death in plants and I demonstrated that it requires a nuclear localization. Similarly, the C-terminal part of RPS4B comprises a nuclear localization signal and is required for RRS1B-RPS4B–dependent AvrRps4 recognition. Interestingly, RPS4TIR+80–mediated cell death can be suppressed by co-expressing RRS1TIR. Using a proteomic approach, I showed that TIR domains and full length RRS1, RPS4, RRS1B and RPS4B can associate in planta forming distinct heterodimers. However, I showed that, despite their homologies, these R proteins only function with their respective pair partner for effector recognition and/or downstream signaling activation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.601060  DOI: Not available
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