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UBC Theses and Dissertations

Characterization of two regulators in plant immune receptor-mediated defense Ao, Kevin


Plants possess a complex multi-layered immune system that enables them to defend themselves against many potential invaders. However, some virulent pathogens can overcome these defenses to cause plant disease. Plant pathogens are a major obstacle to efficient and sustainable global food production. Understanding the underlying molecular mechanisms behind plant immunity will allow precise science-based engineering and breeding of plant disease resistance. Nucleotide-binding leucine-rich repeat proteins (NLRs) are one type of immune receptor that mediate the recognition of pathogens and the activation of defense responses. Although many regulators contributing to NLR homeostasis and activation have been uncovered, our understanding of plant immune signaling is far from complete. One limitation that has hindered gene discovery is genetic redundancy, which can mask immune phenotypes in single mutant plants. Using ectopic overexpression and CRISPR/Cas9-mediated targeted deletion strategies for reverse genetic screens, these limitations can be overcome. In this study, two novel regulators involved in NLR immunity were characterized. The first gene, called SNIPER7 (SNC1-INFLUENCING PLANT E3 LIGASE REVERSE GENETIC 7), was isolated from a previous E3 ubiquitin ligase overexpression screen. SNIPER7 overexpression results in constitutive activation of NLR-mediated defense. SNIPER7 targets the conserved unfoldase CDC48A (CELL DIVISION CYCLE 48A) for degradation. Since CDC48A is involved in the homeostasis of the NLR SNC1 (SUPPRESSOR OF NPR1-1, CONSTITUTIVE 1), SNIPER7 may contribute to immune receptor accumulation upon pathogen infection. The second gene, called TC1b (TRAF CANDIDATE 1b), was isolated from a new CRISPR/Cas9 screen targeting TRAF (TUMOR NECROSIS FACTOR RECEPTOR ASSOCIATED FACTOR) domain containing genes. TRAF domain genes are hypothesized to play a role in plant NLR immunity since many mammalian TRAF domain proteins are involved in innate immunity. TC1b is required for full SNC1 function, but TC1b does not seem to play a role in SNC1 protein homeostasis nor general NLR downstream signalling. The precise molecular function of TC1b is still unclear. Overall, the study of SNIPER7 and TC1b contributes to knowledge of how NLRs like SNC1 are regulated. These findings may be relevant for the precise engineering of NLRs to mediate disease resistance while avoiding growth/yield trade-off from NLR overexpression.

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