Molecular mechanisms of NLR pair-mediated immunity in Arabidopsis

Ma, Yan (2016) Molecular mechanisms of NLR pair-mediated immunity in Arabidopsis. Doctoral thesis, University of East Anglia.

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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
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.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Jackie Webb
Date Deposited: 29 Mar 2017 09:42
Last Modified: 29 Mar 2017 09:42

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