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 <i>Arabidopsis</i> line containing a <i>gstl::luc</i> 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 <i>Pseudomonas syringae </i>pv.<i> tomato (Pst).</i> Strong engagement of the oxidative burst was dependent on the presence of functional <i>Pst hrpS</i> and <i>hrpA</i> 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 <i>gst1::luc</i> 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 <i>RPM1</i> 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 <i>gstl</i> and <i>pall</i> 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 <i>Prla::luc,</i> to uncover a mutant with constitutive defence gene expression. This mutant subsequently, named activated disease resistance 1 (<i>adr1)</i>, was shown to have enhanced resistance to fungal and bacterial pathogens. <i>adr1</i> 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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:651714 |
| Date | January 2000 |
| Creators | Grant, John J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14932 |
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