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Title: Identification and characterisation of Arabidopsis systemic acquired resistance mutants isolated by luciferase imaging
Author: Murray, Shane Louise
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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Plants have evolved a complex series of integrated defence mechanisms against pathogens. Following recognition of a pathogen avirulence (avr) gene product by the corresponding plant resistance (R) gene product, a complex signalling network is initiated. Local inducible defences are activated and a long-distance signal is released, leading to the establishment of systemic acquired resistance (SAR) to a wide range of pathogens. SAR is marked by the accumulation of pathogenesis-related (PR) proteins. Salicylic acid (SA) is a key signalling molecule in SAR, inducing PR gene expression both locally and systemically. In order to study further the molecular basis of SAR, we have developed a method of identifying novel SAR mutants by luciferase imaging. Transgenic Arabidopsis thaliana plants expressing a PR1a-luciferase reporter gene were generated and homozygous seed was chemically mutagenised. Mutants with perturbations in PR1 gene expression were identified and could be divided into various classes. A novel mutant expressing PR1 constitutively was selected for further study. cir1 (constitutively induced resistance 1) expressed both SA-dependent and SA-independent defence genes constitutively, accumulated SA to high levels and produced an increased amount of ethylene. In addition, cir1 exhibited resistance to the virulent bacterial pathogen Pseudomonas syringae pv tomato DC3000 and the virulent oomycete pathogen Peronospora parisitica Noco2. Genetic analyses indicated that cir1 is recessive and defines a mutation in a single gene, cir1 mapped to the lower arm of chromosome 4. Double mutants were produced between cirl and SA-, JA- and ethylene-insensitive mutants. Analysis of these plants showed that SA, JA and ethylene were required for constitutive defence gene expression and disease resistance in cir1. Thus, the results obtained indicate that CIR1 acts as a negative regulator in the disease resistance signal transduction network, most likely functioning upstream of the branchpoint between the SA-dependent and SA-independent pathways.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available