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UBC Theses and Dissertations

Identification and characterization of Receptor-Like Cytoplasmic Kinases (RLCKs) important in NLR-mediated immunity Yaghmaiean, Hoda


Plants have evolved specific strategies to ward off invading pathogens. The plant immune system consists of two conceptual layers: pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). Plasma membrane-localized pattern-recognition receptors (PRRs) and intracellular nucleotide binding-leucine rich repeat receptors (NLRs) are employed as pathogen receptors for pathogen recognition. Additionally, mitogen-activated protein kinase (MAPK) cascades play critical roles in plant immunity. The cascade formed by the Arabidopsis MEKK1-MKK1/MKK2-MPK4 has dual functions in the regulation of immune responses. It is activated during PTI and contributes to basal resistance against virulent pathogens. The whole cascade is guarded by the NLR protein SUMM2. Although recent studies provided important insights into how disruption of the MEKK1-MKK1/MKK2-MPK4 cascade leads to activation of SUMM2-mediated immunity and how SUMM2-mediated immunity is regulated, the signalling components immediately downstream of SUMM2 are largely unknown. Since several kinases most often are involved in the immune signalling events, the potential role of RLCKs as transducing signalling components downstream of CNL SUMM2 was investigated in Arabidopsis. In this study, reverse genetic analysis was carried out on RLCKs with potentially redundant functions to determine whether they are required for SUMM2-mediated defence responses. Using an egg-cell based CRISPR/Cas9 system, I knocked out the candidate RLCK genes in the mekk1-5 ndr1-1 background and identified a small group of RLCKs (designated as KH9.10) that are required for the autoimmune phenotypes of mekk1-5 ndr1-1. This thesis reports the characterization of RLCKs that belong to subgroup VIII. I provide both genetic and biochemical evidence to support the hypothesis that RLCKs in the KH9.10 group play a key role in SUMM2-mediated immunity. In addition, my study shows that this group of RLCKs is required for PTI responses induced by the elicitor flg22. Overall, this work provides new insights into the role of RLCK subgroup VIII as components in the signal transduction network downstream of SUMM2 in Arabidopsis.

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