Post-translational events control pattern recognition receptor trafficking to preserve PAMP responsiveness in plant immunity

Ben Khaled, Sara (2016) Post-translational events control pattern recognition receptor trafficking to preserve PAMP responsiveness in plant immunity. Doctoral thesis, University of East Anglia.

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Pattern recognition receptors (PRRs) are localized at the cell surface to recognize conserved microbial patterns and activate plant immunity. The activation status regulates the localization of ligand-bound PRRs and routing to late endocytic trafficking for vacuolar degradation. This ligand-induced endocytosis is conserved across PRR families, and best characterized for the receptor kinases flagellin-sensing 2 (FLS2) and EF-Tu receptor (EFR), both mediating anti-bacterial immunity. However, the molecular determinants of FLS2 and EFR endocytic trafficking, as well as the biological relevance of these processes remain poorly understood.
In this study, I have dissectedlolo l the molecular code underlying ligand-mediated endocytosis. I show that flagellin induced the interaction of FLS2 with vacuolar protein sorting (VPS) 37-1, a subunit of the endosomal complex required for transport-I (ESCRT-I) that recognizes internalized ubiquitinated proteins for vacuolar sorting. This led me to investigate the role of ubiquitination in FLS2 endocytosis. Using mass-spectrometry and mutational approaches, I identified ubiquitinated FLS2 lysine residues potentially involved in FLS2 endocytic trafficking. Additionally, I revealed an involvement of the E3 ligases keep on going (KEG) and the two redundant plant U-box (PUB) 12 and PUB13 in FLS2 trafficking.
I showed that PUB12/PUB13-mediated monoubiquitination of FLS2 is a key regulatory process for internalisation of activated receptors, while EFR endocytic degradation is regulated by receptor phosphorylation on the tyrosine residues 875 and 877. For both FLS2 and EFR, altering ligand-induced endocytosis did not impact the initiation of downstream signalling, demonstrating that these processes are uncoupled. Instead, my results showed that ligand-mediated endocytosis of FLS2 and EFR plays a pivotal role in maintaining chronic immune signalling responses upon long term ligand stimulation.
Overall, my results uncover an important molecular mechanism regulating the subcellular trafficking of the central immune components FLS2 and EFR, and extend our understanding on how plant responsiveness to its surrounding pathogens is maintained.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Jackie Webb
Date Deposited: 14 Dec 2016 11:17
Last Modified: 08 Nov 2017 01:38


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