Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Popescu, Sorina

Committee Member

Dean, Jefferey F. D.

Committee Member

Li, Jiaxu

Committee Member

Wubben, Martin

Committee Member

Dawe, Angus

Date of Degree

8-6-2021

Original embargo terms

Complete embargo for 2 years

Document Type

Dissertation - Open Access

Major

Molecular Biology

Degree Name

Doctor of Philosophy

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Agriculture and Life Sciences

College

College of Agriculture and Life Sciences

Department

Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Department

Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Abstract

The effector-triggered immunity (ETI) is activated at the site of pathogen infection and results in a state of enhanced immunity called systemic acquired resistance (SAR) in distal, uninfected plant organs. SAR relays on mobile signals transported from infected cells to distal organs, and on signal amplification which supports transcriptional re-programming associated with priming and execution of SAR. Previous research in our lab has identified the chloroplastic TOP1 and cytosolic TOP2 as salicylic acid (SA)–binding oligopeptidases, non-competitively inhibited by SA. We demonstrate that SAR triggered with P. syringae DC3000 AvrRpt2 is abolished in top2 whereas top1 top2 exhibits a SAR slightly but consistently stronger than wild type (WT) controls, indicating that top1 is epistatic to top2. In agreement with the observed SAR phenotypes, top2 is defective in the induction of SAR markers including SA and Pip synthesis and SA signaling genes, whereas top1 top2 shows significantly higher induction of these markers. SAR- phenotype of top2 is rescued by exogenous SA, H2O2 and Pip applications. Interestingly, neither top1 nor top 1top2 are unable to mount SAR in response to Pip and H2O2 treatments. Analysis of ROS-responsive transcription factors and antioxidant gene induction in infected and distal tissues reveal significantly dysregulated patterns in all mutants, with top2 and top1 top2 most affected, indicating that TOP1 and TOP2 function together to support a pattern of successive waves of oxidation and reduction during SAR. The local and systemic oscillations are anti-corelated in Wt. The local vs. systemic anti-correlation is lost in the mutant genotypes. The amplitude of the mRNA oscillations is significantly lower in top2 plants, and significantly increased in top1top2 plants. top1 and top1top2 lost the oscillation compared to WT but they are still able to keep the expression up in time. top2 is unable to support the expression of some of the genes and oscillations and continued the expression of these genes in time. Overall, our results argue for a defining role of TOP chloroplastic and cytosolic proteolytic pathways in maintaining redox signaling necessary for the induction of SAR transcriptional re-programming and execution.

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