9604830 Katagiri, F. Technical section The molecular mechanisms of signal recognition and signal transduction initiation by the nucleotide binding sites (NBS) and the leucine-rich repeats (LRR) encoded in a major class of resistance genes found in plants will be investigated. The model to be tested as a working hypothesis will be the ligand-receptor model. A rapid, quantitative transient expression assay for the resistance gene function has been developed and will be used as the assay for the biological activities of resistance and avirulence genes. Recent findings have suggested that several of the Pseudomomas syringae avirulence genes are sufficient for initiation of the specific resistance response when expressed in plants, suggesting that the avirulence gene products themselves are the specific molecular signals recognized by the resistance gene products. The first major goal is to elucidate the molecular mechanism of recognition of avirulence gene products. That will include the delineation of the polypeptide regions that determine the avirulence gene-specificity of the resistance genes, determination of the smallest domains of the resistance genes (avrRpt2, avrRpm1 and avrB) that are required for their function in plants and investigation of possible physical interactions between the products of resistance and avirulence genes using in vitro binding analysis and/or the yeast two hybrid system. The second major goal is to investigate the mechanism of signal transduction initiation. Mutants, including those which are mutated in the NBS will be generated, characterized and studied. Non-technical section The ultimate goal of this proposal is to elucidate the mechanisms by which plants recognize and respond to avirulent pathogens. The knowledge to be obtained will contribute not only to a better understanding of plant disease resistance mechanisms but also to insight into molecular recognition and signal transduction in general.
