Transposon Tn4431 Mutagenesis of Xanthomonas campestris pv. campestris: Characterization of a Nonpathogenic Mutant and Cloning of a Locus for Pathogenicity. Joe J. Shaw. Department of Plant Pathology, University of California, Davis CA 95616, U.S.A.. Lynette G. Settles, and Clarence I. Kado. Department of Plant Pathology, University of California, Davis CA 95616, U.S.A.. MPMI 1:39-45. Accepted 21 September 1987. Copyright 1987 The American Phytopathological Society.

Mutants of Xanthomonas campestris pv. campestris, the causal agent of black rot of crucifers, were isolated by transposon mutagenesis with Tn4431, which was carried on the suicide vector pSa325. This novel transposon was constructed from a derivative of Tn1721 and contains a promoterless luciferase (lux) operon of Vibrio fischeri, which serves as an unique reporter gene, and a gene that confers tetracycline resistance. Tn4431 facilitates the in vivo construction of transcriptional fusions between the lux operon and bacterial promoters. A nonpathogenic mutant, JS111, was isolated that was able to grow in the excised leaves of cauliflower (like the parent strain) but was unable to grow in attached leaves (unlike the parent strain). JS111 was complemented to full pathogenicity with a clone from a cosmid genomic library of the parent strain. The complementing locus was identified in a 2.1-kb genomic DNA fragment.