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Scientists sequence the plant pathogen Ralstonia solanacearum
By Birgit Reinert


French researchers have sequenced the bacterium that causes southern wilt, one of the most common and devastating plant diseases. The bacterium, Ralstonia solanacearum, infects the root systems of hundreds of plant species worldwide and is capable of destroying entire crops. The sequencing revealed numerous genes that enable the bacterium to attach to plant cells and transfer its proteins into these cells.

Ralstonia solanacearum

Christian Boucher, of the French Institut National de la Recherche Agronomique (INRA), and colleagues sequenced R. solanacearum in part to understand its ability to infect so many different plant species. One reason may be an unexpectedly large number of disease-causing genes. The bacterium has between 40 and 100 'effector' proteins—the molecules used to deliver and spread the toxins that eventually destroy the plant.

Genes related to the organism's virulence are found throughout the genome, which consists of one chromosome and a second molecule about the same size—a megaplasmid. These structures contain 5.8 million base pairs of DNA and about 5,100 genes. The sequenced strain, GMI1000, was isolated from an infected tomato.

"Genome-scale studies carried out on other plant-pathogenic bacteria will soon reveal whether this high number of effectors is correlated with the wide host range of R. solanacearum," the researchers write in Nature.

Bacterial wilt caused by R. solanacearum affects more than 200 different plant species, including tomato, potato, eggplant, and the flowering plant Arabidopsis thaliana. There is no cure. A better understanding of how the organism makes its way into the cells of such a variety of plants will help scientists prevent damage to crops by developing more resistant plants.

The R. solanacearum genome sequence can be viewed online at INRA.

See related GNN articles on other plant pathogens
»The Genome of Agrobacterium tumefaciens: A plant pathogen with a talent for transferring genes
»Genome of bacteria Xylella fastidiosa, a threat to fruit and nut crops, is sequenced

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Salanoubat, M. et al. Genome sequence of the plant pathogen Ralstonia solanacearum. Nature 415, 497-502 (January 31, 2002).

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