Year of Award

9-24-2018

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Biology.

Principal Supervisor

Ng, Danny Wang Kit

Keywords

Arabidopsis thaliana;Plant proteomics;Plant genetics

Language

English

Abstract

WRKY transcription factors (TFs) belong to a large family of regulatory proteins in plants that modulate many plant processes. Extensive studies have been conducted on WRKY-mediated defense response in Arabidopsis thaliana and many crop species. This study aims to investigate the potential roles and contributions of WRKY TFs regulation in improving defense response in the resynthesized Arabidopsis allotetraploids (Arabidopsis suecica) from two related autotetraploid progenitors, Arabidopsis thaliana (At4) and Arabidopsis arenosa (Aa). Upon infection by Pseudomonas syringae (Pst), the allotetraploids has showed enhanced resistance against the pathogen when compared to the parents. Rapid induction of WRKY18, WRKY40, WRKY38, WRKY53, WRKY6; MAP kinase pathway related genes, WRKY33, PAD3; SA-pathway related genes, ICS1, EDS1, PBS3, MYB31; was evident in response to Pst and salicylic acid treatment in the allotetraploids. Cleaved amplified polymorphic sequences analysis further revealed that the AtWRKY18, AaWRKY40, AtWRKY33, and AtWRKY60 alleles expressed at higher levels when compared to their respective homoeologs in the allotetraploids, suggesting potential altered protein-protein interaction networks in the hybrids. Therefore, a split-luciferase complementation assay was used to characterize and quantify protein-protein interaction among these homoeologous WRKYs in the allotetraploids. Results showed that preferential protein-protein interactions exist for the cis-interacting AtWRKY18/AtWRKY18 homodimer or trans-interacting AtWRKY18/AaWRKY40 heterodimer when compared to the respective interacting complexes. In addition, differential affinities of WRKY18 and WRKY40 homo- and hetero- dimers toward the W-boxes at the WRKY60 promoter were observed. In the allotetraploids, PR1 expression was repressed under basal state when compared to the progenitors. Although PR1 is expressed at a higher level in A. thaliana, its expression fold change was higher and faster in the all otetraploids upon salicylic acid treatment. Transient expression of WRKY18 or WRKY40 homodimer in various combinations induced differential expression of PR1 gene in their respective wrky18 and wrky40 Arabidopsis thaliana mutants. In contrast, similar PR1 induction by homodimer in various combinations was observed when they were transiently expressed in the allotetraploids. In addition, transgenic AtWRKY18 overexpression plant displayed enhanced disease resistance against Pst when compared to AaWRKY18 overexpression lines. Such enhanced disease resistance was found to associate with the higher expression of PR1 and PR2 in AtWRKY18 transgenic lines. Moreover, differential Pst-induced expression of the direct targets (ICS1, EDS1 and PBS3) of WRKY18 in the Arabidopsis AtWRKY18 and AaWRKY18 overexpressors supported a biological difference between the At and Aa homodimers in mediating the targets regulation, thus contributing to the difference in disease responses. Overall, our findings suggested that the rapid differential alleles expression and altered protein-protein or protein-DNA interactions of WRKY transcription factors could contribute to the improved defense in the allotetraploids, providing a molecular basis of for heterotic phenotype development in hybrids.

Comments

Principal supervisor: Dr. Danny Wang Kit Ng ; Thesis submitted to the Department of Biology ; Thesis (Ph.D.)-Hong Kong Baptist University, 2018.

Bibliography

Includes bibliographical references (pages 134-150).

Available for download on Friday, February 26, 2021



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