Requirement for phosphoglucose isomerase of Xanthomonas campestris in pathogenesis of citrus canker

A mutant (XT906) of Xanthomonas campestris pv, citri, the causal agent of c itrus canker, was induced by insertion of the transposon Tn5tac1 and isolat ed. This mutant did not grow or elicit canker disease In citrus leaves but was still able to induce a hypersensitive response in a nonhost plant (the common bean). The mutant was also unable to grow on minimal medium containi ng fructose or glycerol as the sole carbon source. A 2.5-kb fragment of wil d-type DNA that complemented the mutant phenotype of XT906 was isolated. Se quence analysis revealed that this DNA fragment encoded a protein of 562 am ino acids that shows homology to phosphoglucose isomerase (PGI), Enzyme act ivity assay confirmed that the encoded protein possesses PGI activity. Anal ysis of the activity of the promoter of the pgi gene revealed that it was i nhibited by growth in complex medium but induced by culture in plant extrac t. These results demonstrate that PGI is required for pathogenicity of X. c ampestris pv. citri.