Molecular Analysis of Avirulence and Basic Pathogenicity Genes in Xanthomonas Campestris pv Vesicatoria

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The ability of avirulent isolate of Xanthomonas campestris pv. vesicatoria to induce a hypersensitive reaction on near- isogenic resistant cultivars of Capsicum annuum or widely divergent species is controlled by the presence of specific avirulence genes. In this proposal, we plan to characterize the race-specific avirulence genes, avrBs1 and avrBs2, and a member of unique class of non-host avirulence genes, avrZ. The molecular characterization of these genes will provide a solid molecular foundation which will allow us to compare structural similarities or differences in protein products and regulation of avirulence gene expression. The characterization of these genes and the production of polyclonal antisera to their respective proteins will put us into a position to design experiments to elucidate the biochemical processes involved in cellular recognition and the subsequent signal transduction processes responsible for eliciting plant defence mechanisms. The complementation analysis of the Hrp gene cluster and its possible functional relationship with specific avirulence genes will addressed by defining the genetic organization of this region of DNA and the effects of specific mutations on the regulation of avirulence gene expression. Finally, we will investigate the molecular genetic control of host range exclusion in X. c. vesicatoria on non-host species and determine the inheritance patterns of plant host genes that determine resistance. Many plant pathogens follow a "gene-for-gene" relationship with regard to whether or not they cause disease in a particular strain of host plant. Disease ensues only when the pathogen carries a specific allele of one of its own genes, and when the host carries a specific allele of one of its own genes. Any combination of other alleles of these particular pathogen and host genes precludes disease. This genetic relationship has been understood for forty years, but the biochemical functions of the genes involved in the determination of the occurrence of disease have remained completely obscure. Dr. Staskawicz has been one of the first investigators to succeed in isolating disease- determining genes from a plant pathogen. In this project he will characterize the products of these genes, in order to lay the foundation for understanding of the molecular basis of the host-pathogen interaction. Apart from its intrinsic biological interest, this work also has obvious practical importance for future efforts to control plant diseases.