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Veggie Spoilers: Two Genomes for the Price of One
By Kate Dalke

Bacterial speck, seen above, is a problem in cold, moist climates.

Ripe tomatoes are a summer pleasure. But some tomatoes never make it to market because bacteria infect the plants and cause unappetizing black pocks on the fruit.

The disease, called bacterial speck, occurs worldwide wherever tomatoes are grown. It can devastate farmers, damaging half the crops in a harvest.

Bacterial speck is particularly problematic to farmers in Northern climates, where the bacteria thrive in cold, moist conditions.

Now, to better understand how the bacterium causes disease, scientists have sequenced the genome of this tomato spoiler, whose scientific name is a mouthful: Pseudomonas syringae pathovar tomato DC3000.

The genome sequence is being used to study how the bacterium infects plants. In a new study, researchers compared the bacterium to two close relatives: a bacterium that infects the lungs of people with cystic fibrosis (Pseudomonas aeruginosa) and a harmless soil bacterium (Pseudomonas putida).

The researchers identified nearly 300 genes that help the bacterium infect plants, such as genes involved in injecting proteins into plant cells and interfering with plant defenses.

An initial draft of the bacterium’s genome has been available online for more than a year, and scientists around the world have mined the data for genes. In the span of 18 months, eight separate papers that use the sequence have been published.

“The whole community jumped on [the genome] and created a momentum that was really special,” says Alan Collmer of Cornell University, who co-led the project with Robin Buell of The Institute for Genomic Research in Rockville, Maryland, where the sequencing was done.

The tomato pathogen also infects another plant, called Arabidopsis thaliana, which was the first plant to be sequenced. Now, with the genomes of both species, researchers can study the genetics of infection from the perspective of both pathogen and host.

The project was funded by the National Science Foundation’s Plant Genome Research Program and came in under budget. TIGR researchers are using the extra money to sequence the genome of a different strain that infects beans.

“In effect, the National Science Foundation will have gotten two genomes for the price of one,” says Collmer.

The genome of the strain that infects beans is expected in early 2004.

—Related Information—

Pseudomonas syringae Genome Biology Resource

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Buell, C. R. et al. The complete genome sequence of the Arabidopsis and tomato pathogen Pseudomonas syringae pv. tomato DC3000. Proceedings of the National Academy of Sciences USA 100

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