Theses and Dissertations

ORCID

0000-0002-8387-8171

Advisor

Popescu, George

Committee Member

Peterson, Daniel

Committee Member

Li, Ling

Committee Member

Dong, Xinnian

Date of Degree

8-12-2026

Original embargo terms

Embargo 2 years

Document Type

Dissertation - Open Access

Major

Life Sciences (Biochemistry)

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Agriculture and Life Sciences

Department

Department of Biochemistry, Nutrition and Health Promotion

Abstract

Redox-regulated proteolysis emerged as an important layer of immune control in Arabidopsis thaliana, linking peptide turnover, salicylic acid-associated signaling, and transcriptional reprogramming during both effector-triggered immunity and systemic acquired resistance. Thimet oligopeptidases TOP1 and TOP2, previously implicated in redox-sensitive and salicylic acid-responsive immune pathways, were examined here as candidate regulators of defense coordination at multiple levels, from peptide generation to promoter activity and whole-transcriptome dynamics. Functional testing of TOP-associated candidate peptides supported the view that immune-related proteolysis is not solely degradative but can produce endogenous fragments with the potential to influence pathogen restriction and immune output. To define how redox-sensitive proteolysis is connected to defense gene regulation, promoter::LUC reporter lines were developed for selected systemic acquired resistance-associated genes and monitored in vivo following Pseudomonas syringae pv. tomato DC3000 carrying avrRpt2 treatment. Real-time luminescence analyses revealed that promoter activation in systemic tissues is highly dynamic and depends on genotype, with altered magnitude, timing, and persistence of transcriptional responses in the redox-defective top2 background. Integration of targeted qPCR, promoter-reporter assays, and Quant-seq analysis further resolved systemic acquired resistance into temporally distinct transcriptional phases rather than a single uniform defense response. Early intervals were marked by rapid induction of redox- and stress-associated genes, including GRXS13 and ZAT10, whereas later stages were characterized by stronger salicylic acid-amplified defense output, particularly through PR1. The broader Quant-seq candidate panel reinforced this interpretation by identifying interconnected modules associated with salicylic acid signaling, redox homeostasis, receptor-linked amplification, and late defense output. Together, these findings support a mechanistic model in which TOP-dependent redox-sensitive proteolysis contributes to immune robustness by shaping peptide homeostasis, promoter activation, and the temporal structure of systemic transcriptional responses. This framework positions TOP proteases as regulatory nodes linking intracellular redox biology to long-distance immune signaling and the establishment of defense in plants.

Sponsorship (Optional)

National Sanitation Foundation (NSF)

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