The rpoN Gene of Xanthomonas campestris pv. vesicatoria Is Not Required for Pathogenicity. Torsten Horns. Institut fur Genbiologische Forschung Berlin GmbH, 14195 Berlin, Germany. Ulla Bonas. Institut des Sciences Vegetales, Centre National de la Recherche Scientifique, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France. MPMI 9:856-859. Accepted 27 August 1996. Copyright 1996 The American Phytopathological Society.

We have cloned the rpoN region of the pepper and tomato pathogen Xanlhomonas campestris pv. vesicatoria to analyze its role in pathogenicity and hrp gene activation. Open reading frame 3 (ORF3) from this region is predicted to encode a protein that is up to 45% identical and 65% similar to previously described RpoN proteins and was shown to be essential for the utilization of nitrate as sole nitrogen source. The X. campestris pv. vesicatoria rpoN gene is, however, not required for pathogenicity and hrp gene expression.