1.4.36
IDENTIFICATION OF SYSTEMIC ACQUIRED RESISTANCE MUTANTS IN ARABIDOPSIS BY LUCIFERASE lMAGING

C THOMPSON, S MURRAY, N READ and G LOAKE

Institute of Cell and Molecular Biology, King's Buildings, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JH, UK

Background and oblectives
Plants have evolved a complex series of integrated defence mechanisms, which are employed to resist the establishment of disease in response to potential pathogens. Pathogen recognition is genetically determined, a given plant resistance (R) gene recognizing the product of a specific pathogen avirulence (avr) gene. This interaction activates a complex underlying signalling network, initiating the local deployment of inducible defences, including hypersensitive cell death (HR). Moreover, a long-distance signal is released, leading to the establishment, over several days, of resistance to secondary infections from a broad spectrum of pathogens throughout the plant. This phenomenon has been termed systemic acquired resistance (SAR). The establishment of local and systemic acquired resistance is marked by the expression of so-called SAR genes, which encode pathogenesis-related (PR) proteins. The plant metabolite salicylic acid (SA) has been proposed to function as a key signalling molecule in this process, inducing the expression of local and systemic SAR genes. Recently deployed mutant screens have uncovered a small number of Arabidopsis mutants compromised in their response to SA. However, the molecular basis of the SAR signalling pathway remains largely undetermined. Here we describe the development of a strategy employed to identify novel SAR signalling mutants by luciferase imaging.

Materials and methods
The Arabidopsis PR1 promoter was cloned and subsequently used to create a chimaeric PRI-luciferase reporter gene (PRILUC). Approximately 10,000 seeds from a homozygous line were mutagenized using EMS. M2 plants were screened for perturbations in PRI gene expression following inoculation with avirulent pathogen 5.

Results and conclusions
A strategy has been developed to image, in real time, the establishment of SAR in living plants. Associated mutant screens have identified a number of putative Arabidopsis SAR mutants, which are currently being characterized.