By
Edward R. Winstead

May 24, 2002

Brazilian researchers have sequenced two major plant pathogens of the genus Xanthomonas. Each species preys on different crops and infects plants in different ways, but the two genomes have 80 percent of their genes in common. Among the remaining 20 percent, the researchers identified genes that may underlie each strain's preference for infecting certain plants and its distinct mode of infection.

Citrus canker fruit lesion. Image credit: Fundecitrus - Brazil

The first bacterium is Xanthomonas axonopodis pv. citri—known as Xac—which causes citrus canker in oranges, lemons and other members of the citrus family. The second is Xanthomonas campestris pv. campestris—known as Xcc—which causes black rot in crucifer plants, such as cabbages, sprouts, and broccoli.

The Xcc bacterium also infects weeds, including Arabidopsis thaliana, which has been sequenced and is the model species used in plant research. Researchers can now test hypotheses about genes associated with plant infections using the publicly available genome sequences of the plant pathogen (Xcc) and one of its hosts (Arabidopsis).

The study was led by João Carlos Setubal and João Paulo Kitajima of the Universidade Estadual de Campinas in São Paulo. The research is part of the Xanthomonas Genome Project, whose goals include the development of new strategies for fighting economically significant plant pathogens.

"Comparative analysis between the two Xanthomonas strains allowed us to identify a set of strain-specific genes, some of which are probably responsible for the distinct pathogenicity and host specificity profiles of these organisms," the researchers write in Nature.

Black rot cabbage foliar lesion. Image credit: IAPAR - Brazil

Xanthomonas axonopodis pv. citri has one circular chromosome comprising 5.1 million base pairs and two smaller DNA structures, or plasmids. Xanthomonas campestris pv. campestris has a slightly smaller chromosome (5 million base pairs) and no plasmids.

For more information visit the Xanthomonas Genome Project Web site

See related GNN articles
»Scientists sequence the plant pathogen Ralstonia solanacearum
»Genome of bacteria Xylella fastidiosa, a threat to fruit and nut crops, is sequenced

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da Silva, A.C.R. et al. Comparison of the genomes of two Xanthomonas pathogens with differing host specificities. Nature 417, 459-463 (May 23, 2002).

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