A GENE FOR SUPEROXIDE-DISMUTASE FROM XANTHOMONAS-CAMPESTRIS PV CAMPESTRIS AND ITS EXPRESSION DURING BACTERIAL-PLANT INTERACTIONS

A recombinant plasmid selected from a library of Xanthomonas campestri s pv. campestris genomic DNA by functional complementation of a supero xide dismutase (SOD)deficient strain of Escherichia coli contained a g ene encoding the major SOD activity of X. campestris pv, campestris. I nhibition and renaturation studies suggested that manganese was the me tal cofactor for this SOD. Examination of the nucleotide sequence of a n active subclone revealed a 612-bp open reading frame that encodes a protein with high amino acid sequence homology to a range of SOD enzym es. The sod gene was mutagenized with Tn5-lacZ, None of the insertions that abolished SOD-conferring activity were in the correct orientatio n for lacZ expression, Repeated attempts to introduce these insertions into the chromosome of X. campestris pv, campestris were unsuccessful and it was concluded that the sod gene may be essential for viability , In order to monitor the expression of the sod gene, a sod-gus transc riptional fusion was constructed, Expression of the sod gene varied ac cording to the growth stage of the organism in culture, In planta, the sod gene was induced within 3 to 4 h of inoculation, with similar kin etics during compatible and incompatible interactions with turnip and pepper, respectively.