The Role in Pathogenicity of Some Related Genes in Xanthomonas campestris Pathovars campestris and translucens: A Shuttle Strategy for Cloning Genes Required for Pathogenicity. Maria K. Sawczyc. John Innes Institute, Norwich NR4 7UH, U.K.. Christine E. Barber, and Michael J. Daniels. John Innes Institute, Norwich NR4 7UH, U.K. . MPMI 2:249-255. Accepted 1 May 1989. Copyright 1989 The American Phytopathological Society.

To determine whether Xanthomonas campestris pathovars possess related pathogenicity genes, a genomic library of DNA of X. campestris pv. translucens (constructed in the cosmid pLAFR1) was mobilized into nonpathogenic mutants of X. campestris pv. campestris, 8237 and 8288. Two unrelated X. c. pv. translucens clones, pIJ3021 and pIJ3022, restored pathogenicity of the mutants to turnips and production of protease by mutant 8237. pIJ3021 was homologous to pIJ3020, a cosmid containing X. c. pv. campestris DNA known to complement 8237. A Tn5 insertion in pIJ3022 that abolished the ability to restore function to 8237 was transferred by marker exchange into the genome of X. c. pv. translucens, yielding a strain that had lost pathogenicity to wheat. Pathogenicity of mutant 8288 was restored by the X. c. pv. translucens clone pIJ3003. A Tn5 insertion in pIJ3003 that abolished the restoration of pathogenicity to 8288 was also transferred to the X. c. pv. translucens genome, but the resulting mutant retained pathogenicity to wheat. In addition, transconjugants arising from mass reciprocal transfer of X. c. pv. campestris and X. c. pv. translucens libraries into the heterologous pathovars were tested for modification of pathogenicity to the homologous and heterologous plant hosts (that is, extension or restriction of host range), but no clones showing reproducible effects were found.