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Title: A genetic dissection of signal transduction pathways underlying the oxidative burst, cognate redox signalling, and establishment of systemic acquired resistance
Author: Grant, John J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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Recognition of avirulent microbial pathogens activates an oxidative burst, leading to the accumulation of reactive oxygen intermediates (ROIs), which are thought to integrate a diverse set of defence mechanisms resulting in the establishment of plant disease resistance. Two contrasting experimental strategies were devised to dissect genetic mechanisms governing these signal transduction pathways. Firstly, a novel transgenic Arabidopsis line containing a gstl::luc transgene was developed and employed to report the temporal and spatial dynamics of ROI accumulation and cognate redox signalling in response to attempted infection by avirulent strains of Pseudomonas syringae pv. tomato (Pst). Strong engagement of the oxidative burst was dependent on the presence of functional Pst hrpS and hrpA gene products. Experiments employing specific pharmacological agents suggested at least two distinct sources, including a NADPH oxidase and a peroxidase-type enzyme, contributed to the generation of redox cues. The analysis of gst1::luc gene expression in specific mutant backgrounds suggested engagement of the oxidative burst and cognate redox signalling functioned independently of ethylene, salicylic acid and methyl jasmonate in local RPM1 mediated resistance. In contrast, studies using a panel of specific protein kinase and phosphatase inhibitors revealed mitogen activated protein kinase kinase (MAPKK) activity was required for the activation of the ROI-regulated genes gstl and pall in response to redox cues. Thus the engagement of a redox signalling network dependent on MAPKK activity may contribute to the establishment of plant disease resistance and the development of cellular protectant mechanisms. Secondly, Activation Tagging was employed in conjunction with the reporter gene line Prla::luc, to uncover a mutant with constitutive defence gene expression. This mutant subsequently, named activated disease resistance 1 (adr1), was shown to have enhanced resistance to fungal and bacterial pathogens. adr1 mutants were also shown to have enhanced drought tolerance, and as such are believed to be the first plants engineered with elevated resistance to both disease and drought stress.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available