Regulatory Mechanism of Genetic Regioo (hrp) Controls Both Plant Pathogenicity and Hyper-sensitive Reaction.

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1. From the analyzes of non-pathogenic mutants of Xanthomonas campestris pv.citri induced by Tn5 trasposon tagging and of cosmid clones, it became apparent that this pathogen has two different hrp regions ; one (hrpl) consists of relatively small region and other (hrp2) consists of 25kb region containing multiple hrp genes. 2. hrpl showed homology with the gene for glucosyl-transferase of Escherichia coli, and it was considered to be involved in glucan synthesis. Furthermore, glucan of this pathogen was cyclic glucan similar to the one of Agrobacterium tumefascines and Rhizobiaceae. This indicates that this pathogen may require the adsorption to plant cells by glucan for the inductions of pathogenicity and hypersensitive reaction. 3. hrp2 hybridized with hrp of Pseudomonas solanacearum.hrp2 was turned out to be a good probe for RFLP analysis to identify species and pathovars of Xanthomonas. The clone which complements F8 could be obtained. 4. Using gene fusion with phoA, it was suggested that the induction of hrp2 requires the exposure to plant cells. 5. Since the importance of early reaction was thought to be important, the chemiluminescence due to the formation of free radicals was investigated. From this study, it was found that this pathogen produces both heat-stable elicitor and suppressor.