Roles and mechanisms of effector-triggered immunity in plant disease resistance

Ngou, Pok (2020) Roles and mechanisms of effector-triggered immunity in plant disease resistance. Doctoral thesis, University of East Anglia.

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The plant immune system involves extracellular receptors that detect pathogen-derived molecules, and intracellular receptors that recognize pathogen-secreted effectors. Surface receptor-mediated immunity, or PTI, has been extensively studied but intracellular receptor-mediated immunity, or ETI, has rarely been investigated in the absence of PTI. Previous studies on ETI have mostly been concluded from comparison between PTI and ‘PTI + ETI’. Intracellular nucleotide-binding leucine-rich repeat (NLR) proteins activate ETI following recognition of pathogen-secreted effectors. The mechanisms by which NLR activation leads to pathogen resistance are largely unknown. An Arabidopsis line with inducible expression of the effector AvrRps4 has been generated to investigate the downstream immune responses triggered by the TIR (Toll-like, Interleukin-1 receptor, Resistance protein)-NLRs RRS1 and RPS4. Activation of ETIAvrRps4 leads to upregulation of defence genes and enhanced resistance against Pseudomonas syringae, but does not lead to physiological responses such as ROS burst, MAPKs activation or macroscopic cell death. This implies that robust physiological changes during ‘PTI + ETI’ might be due to the interaction between PTI and ETI. Using the inducible-effector system, I discovered a mutual-potentiation relationship between PTI and ETI. PTI activates multiple protein kinases and NADPH oxidases to induce physiological responses, whereas ETI potentiates the activation of these signalling components during ‘PTI + ETI’. Multiple PTI signalling components are highly upregulated during ETI through multiple mechanisms. Reciprocally, hypersensitive response triggered by ETI is enhanced by PTI. Activation of either PTI or ETI alone is insufficient to provide resistance against P. syringae. Thus, PTI and ETI mutually potentiates each other to provide robust resistance. These findings on the relationship between the two immune systems reshape our understanding of plant immunity.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 19 Oct 2021 07:58
Last Modified: 19 Oct 2021 07:58


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