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Title: Mechanism of host cell death interference by fungal RALPH effector in cereal powdery mildew infection
Author: Przydacz, Michal Maria
ISNI:       0000 0004 8499 6545
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Global food security is threatened by impending climate change, limited agricultural land and resources, and by an increase in human population disproportional to the increase in food production. One way to increase food production is to decrease crop yields lost to pathogens. Blumeria graminis is an obligate biotrophic fungal pathogen that causes powdery mildew in wheat and barley. It is an economically important phytopathogen that employs over 500 effectors to facilitate infection by subduing the plant immune system. In particular, RNase-like effector proteins associated with haustoria (RALPHs), such as BEC1054/CSEP0064, are thought to play a crucial role in Blumeria infection. I hypothesised that BEC1054 facilitates infection by inhibiting host cell death via host ribosome binding. This study focuses on the relationship between RALPH effector BEC1054 and the barley Jasmonate-induced protein 60 (JIP60), whose N-terminal domain acts as a ribosome-inactivating protein (RIP). JIP60 probably induces host cell death by depurination of the SRL site on the 28S rRNA subunit, leading to ribosome inactivation and translation inhibition. In plants exposed to methyl-jasmonate, a phytohormone that induces expression of JIPs and results in senescence, host rRNA degradation was inhibited in transgenic wheat expressing BEC1054. Transient expression of active recombinant JIP60, via agroin ltration, mediates host cell death in nonnative Nicotiana benthamiana. Conversely, co-expression of BEC1054 with JIP60 in N. ben- thamiana inhibits the JIP60 RIP-mediated necrosis. So far, no speci c residues have been identi ed that are involved in BEC1054 function. Therefore, I propose BEC1054 effector employs a mode of action based on non-speci c factors, such as structural compatibility with its targets and hydrophobic interactions, rather than complementary hydrophilic residues. The main function of BEC1054 is to bind host ribosomes and occlude the SRL site. This then inhibits host RIPs from performing rRNA cleavage, which would lead to ribosome inactivation, host cell death and prevent establishment of infection.
Supervisor: Spanu, Pietro ; Cota, Ernesto Sponsor: Biotechnology and Biological Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral