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Title: Molecular mechanisms of NLR pair-mediated immunity in Arabidopsis
Author: Ma, Yan
ISNI:       0000 0004 6059 9131
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2016
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Central to plant survival is the ability to activate immunity upon pathogen perception. Plants deploy immune receptors to recognise specific pathogenderived molecules (effectors) and to trigger defence. These receptors usually recognise a specific effector, but some work in pairs and can detect multiple effectors. The Arabidopsis RRS1-R/RPS4 receptor pair forms an immune complex, conferring recognition of two distinct bacterial effectors, AvrRps4 and PopP2. A paralogous pair linked to RRS1/RPS4, designated as RRS1B/RPS4B, only recognises AvrRps4. My work has revealed that both pairs detect AvrRps4 via an integrated WRKY domain of RRS1 or RRS1B, which mimics the effector’s host targets: the WRKY transcription factors (TF). It has also been shown that the WRKY TF-targeting PopP2 is also perceived by the RRS1-R WRKY domain. Together, we suggest that RRS1 (or RRS1B) with the WRKY domain fusion has evolved to protect defence-regulating WRKY proteins from being attacked by effectors. These integrated domains of immune receptors are becoming popular targets for synthetic resistance engineering. However, one of the biggest challenges is to avoid auto-activity while enabling new recognition capacity when manipulating the integrated domains. To better understand how these receptors operate to convert effector perception into defence activation, I investigated the dynamic molecular interactions in the pre-activation complex, and those that change upon effector perception. I found that RRS1-R/RPS4 complex is negatively regulated by the WRKY domain during pre-activation, and effector-triggered activation is likely mediated by de-repression of the WRKY domain. After effector-triggered RRS1 de-repression, the activation signal is transduced to RPS4. Domain swaps between RRS1-R/RPS4 and RRS1B/RPS4B have revealed the key interaction required for this transduction is between RRS1 domain 4 and the RPS4 C-terminal domain. Furthermore, I discovered possible distinct domain-domain interactions that enable AvrRps4- and PopP2- triggered activation. The mechanistic insights into complex auto-inhibition and activation described in this thesis will prove valuable for many other cooperative immune receptor systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available