In the 23 May Nature, da Silva et al. report the comparative analysis of genomes of two bacterial phytopathogens that differ in their host specificity and pathogenicity (Nature 2002, 417:459-463).

Xanthomonasaxonopodis pv citri (Xac) affects citrus cultivars and causes canker lesions. In contrast, Xanthomonas campestris pv. campestris (Xcc) affects crucifers and causes black rot. Each genome contains a circular chromosome of around 5 megabases. In addition, Xac carries two plasmids, of 34 and 65 kilobases. The chromosomes display a high degree of colinearity, suggesting as few as three major rearrangement events have occurred in the time that separates them, and they have as many as 80% of genes in common. Regions around the putative termini of replication contain most strain-specific genes that may be related to pathogenesis. Xac-specific genes include those for fungicide synthesis, secreted toxins, and nodulation pathways. Xcc-specific...

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