Isolation of a Gene Cluster from Xanthomonas campestris pv. vesicatoria that Determines Pathogenicity and the Hypersensitive Response on Pepper and Tomato. Ulla Bonas. Institut für Genbiologische Forschung Berlin GmbH, 1000 Berlin 33, Federal Republic of Germany. Ralf Schulte(1), Stefan Fenselau(1), Gerald V. Minsavage(2), Brian J. Staskawicz(3), and Robert E. Stall(2). (1)Institut für Genbiologische Forschung Berlin GmbH, 1000 Berlin 33, Federal Republic of Germany; (2)Department of Plant Pathology, University of Florida, Gainesville 32611 U.S.A; and (3)Department of Plant Pathology, University of California, Berkeley 94720 U.S.A. MPMI 4:81-88. Accepted 2 October 1990. Copyright 1991 The American Phytopathological Society.

Nonpathogenic mutants of Xanthomonas campestris pv. vesicatoria that had lost the ability to induce a hypersensitive response in resistant host plants and in nonhosts were complemented by clones from a wild-type library. Analysis of transposon insertion mutants defined a 25-kilobase region of the genome of X. c. pv. vesicatoria, which is necessary for the interaction of the bacterium with the plant. The genes in this region were designated hrp genes. Complementation studies revealed that the hrp region is organized into at least six different complementation groups. Southern blot experiments showed that DNA sequences homologous to a 23-kilobase region from the hrp cluster were present in other pathovars of X. campestris. In some pathovars homology was high enough to permit marker gene exchange or complementation of nonpathogenic mutants by X. c. pv. vesicatoria sequences. Cross-hybridization between the hrp sequences of X. c. pv. vesicatoria and genomic DNA of different species of Pseudomonas was not observed.