USE OF ARABIDOPSIS-THALIANA AND PSEUDOMONAS-SYRINGAE IN THE STUDY OF PLANT-DISEASE RESISTANCE AND TOLERANCE

The interaction between Arabidopsis thaliana and the bacterium Pseudom onas syringae is being developed as a model experimental system for pl ant pathology research. Race-specific (''gene-for-gene'') resistance h as been demonstrated for this interaction, and pathogen genes that det ermine avirulence have been isolated and characterized. Because certai n lines of both Arabidopsis and soybean are resistant to bacteria carr ying the avirulence genes avrRpt2 and avrB, extremely similar pathogen recognition mechanisms are apparently present in these two plant spec ies. Isogenic bacterial strains that differ by the presence of single avirulence genes are being used to analyze plant resistance. Plant res istance genes have been identified in crosses between resistant and su sceptible lines. The extensive map-based cloning tools available in Ar abidopsis are being used to isolate these resistance genes. In a relat ed project, ethylene-insensitive Arabidopsis mutants are being used to examine the role of ethylene in disease development. Ethylene apparen tly mediates symptom formation in susceptible plants and is not requir ed for resistance, suggesting possible strategies for enhancement of d isease tolerance in crops.