Elicitation and evasion of plant innate immunity by beneficial and pathogenic bacteria

Pfeilmeier, Sebastian (2017) Elicitation and evasion of plant innate immunity by beneficial and pathogenic bacteria. Doctoral thesis, University of East Anglia.

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Plasma membrane-localized pattern recognition receptors (PRRs) are central components of the plant innate immune system. PRRs perceive characteristic microbial features, termed pathogen-associated molecular patterns (PAMPs), leading to pattern-triggered immunity (PTI). As PAMPs from both pathogenic and beneficial bacteria are potentially recognized, both must employ strategies to evade and/or suppress PTI. Here, I show that exopolysaccharides (EPS) and flagella-driven motility, both of which are regulated by the secondary messenger cyclic-di-GMP, are important virulence factors at different stages during Pseudomonas syringae pv. tomato (Pto) DC3000 infection of Arabidopsis thaliana. High levels of cyclic-di-GMP impaired flagellin accumulation in different Pseudomonas species, and helped bacteria to evade recognition by the PRR FLAGELLIN SENSING 2. In this case, immune evasion was fully explained by the effect of cyclic-di-GMP on flagellin synthesis rather than on EPS production. Nevertheless, an EPS-deficient Pto DC3000 mutant, Δalg/psl/wss, showed compromised virulence, and a combination of two types of EPS appeared to be required for optimal in planta proliferation. In a complementary project, I tested whether PAMP recognition affects the interaction between the legume Medicago truncatula and its symbiotic partner Sinorhizobium meliloti. I transferred the PRR EF-TU RECEPTOR (EFR) from A. thaliana to M. truncatula, conferring recognition of the bacterial EF-Tu protein. Expression of EFR protected M. truncatula against the root pathogen Ralstonia solanacearum without compromising the overall symbiotic interaction with nitrogen-fixing S. meliloti. My results indicate that rhizobium either avoids PAMP recognition, or actively suppresses immune signalling during the infection process. Finally, I engineered a PAMP in S. meliloti by replacing the eliciting inactive flg22 epitope (derived from flagellin) with an eliciting epitope. My results suggest that legumes can be engineered with novel PRRs, as a biotechnological approach for broad-spectrum disease resistance, without perturbing the nitrogen-fixing symbiosis. Overall, my work contributes to our understanding of the molecular interaction between plants and bacteria.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Jackie Webb
Date Deposited: 01 May 2018 09:46
Last Modified: 01 May 2018 09:46
URI: https://ueaeprints.uea.ac.uk/id/eprint/66876


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