Chromosomal gene transfer by conjugation in the plant pathogen Xanthomonasaxonopodis pv. vesicatoria

Genes for copper resistance, located on the chromosome of strain XvP26 of X anthomonas axonopodis pv. vesicatoria, were transferred by conjugation to a recipient strain of the bacterium. The chromosomal gene transfer was verif ied by analyses of the genomes of donor, recipient, and putative transconju gants for plasmid profiles, by polymorphism of DNA bands obtained by digest ing total genomic DNA by a rare-cutting endonuclease and pulsed-field gel e lectrophoresis, and by Southern hybridization with a probe containing the c opper genes. Transfer of kanamycin resistance to a recipient strain, associ ated with Tn5 insertion into the chromosome of another strain of the bacter ial spot pathogen, was also verified. The frequency of kanamycin resistance transfer to recipient was more than 75 times greater in pepper leaves than in vitro. The transfer of chromosomal sequences containing the hypersensit ive reaction and pathogenicity (hrp) genes and pigmentation (pig) genes was linked with transfer of kanamycin resistance (Tn5). Horizontal transfer in planta of the chromosomal genes (i.e., cop, pig, hrp, and Tn5 sequences) a mong strains of X, axonopodis pv, vesicatoria means that horizontal chromos omal gene transfer is possible in nature. This type of gene transfer may ex plain the presence of great diversity among strains of the bacterial spot p athogen in terms of DNA polymorphism and may also explain the apparent hori zontal transfer of hrp sequences among pathovars of Xanthomonas.