Identification and DNA Sequence of a Pathogenicity Gene of Xanthomonas campestris pv. campestris. A. E. Osbourn. Sainsbury Laboratory, John Innes Institute, Norwich NR4 7UH, U.K.. B. R. Clarke, and M. J. Daniels. Sainsbury Laboratory, John Innes Institute, Norwich NR4 7UH, U.K.. MPMI 3:280-285. Accepted 20 March 1990. Copyright 1990 The American Phytopathological Society.

A region of Xanthomonas campestris pv. campestris DNA containing at least two pathogenicity genes was identified. Mutants in one gene were clearly reduced in pathogenicity while mutants in the other were only moderately reduced. Both classes of mutants were prototrophic and motile, and had wild-type levels of extracellular enzymes and extracellular polysaccharide. They also grew in vitro and in planta at the same rate as the wild type. Experiments involving one of the clear pathogenicity mutants indicated that the recovery of mutant cells from turnip seedlings 24 hr after inoculation was lower than for the wild type. This may be due to cell death as a result of action by some preformed or induced plant factor. From DNA sequencing an open reading frame was identified that encompassed the site of the mutations giving a clear reduction in pathogenicity. The predicted protein sequence had no homology with other proteins in the computer data base.