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Drink to genomics
By Kate Dalke

The next time you savor a glass of California wine, toast genomics. Thanks to new genomic information, wine growers may someday have new weapons against a microbe that destroys grape vines. The bacterium, called Xylella fastidiosa, can wipe out an entire vineyard.

The genome of the bacterium has been sequenced, and among the newly identified genes are some that are essential for infecting plants. Once inside the plant, the bacteria cut off water to the leaves, destroying the fruit and causing Pierce's disease.

"Pierce's is at the top of our list in terms of diseases," says Patrick Gleeson, executive director for the American Vineyard Foundation in Napa, California. Wine is a $33 billion industry in California.

Wine growers currently fight Pierce's disease using insecticides and by pruning diseased portions of a vine. Chardonnay and Pinot Noir grapes are particularly vulnerable to Pierce's disease, though it is not clear why.

Southern California has been hard hit by Pierce's disease. The region has been invaded by the glassy-winged sharpshooter, an insect that carries the bacteria in its gut. The sharpshooter transmits the bacteria directly into the grapevines.

Xylella fastidiosa is unique among plant pathogens because it infects a variety of plants, from grapes and almonds to oranges and oleander. It has destroyed crops from California to Argentina.

In fact, Pierce's disease was such a problem in South America that in 2000 Brazilian researchers sequenced the Xylella strain that attacks oranges. The USDA then asked the Brazilian team to sequence the strain that infects California grapevines.

In a new study, published in Journal of Bacteriology, the scientists compared the orange and grape strains. The genomes are similar, but certain segments have been rearranged, says Marie-Anne Van Sluys, who led the research at the University of São Paulo in Brazil.

The scientists found genes that may help the bacterium attach to plant cells and to the sharpshooter's gut.

Another group of researchers from the US Department of Energy's Joint Genome Institute in Walnut Creek, California, partially sequenced the genomes of the almond and oleander strains in September 2002.

The USDA is now comparing the genomes of the citrus and grape strains to the almond and oleander. The comparison may reveal clues about how the bacteria infect specific plants and lead to new anti-bacterial measures.

See related GNN articles
»New strains of plant and nut pathogen yield their genomes
»Genome of bacteria Xylella fastidiosa, a threat to fruit and nut crops, is sequenced

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Van Sluys, M.A. et al. Comparative analyses of the complete genome sequences of Pierce's disease and citrus variegated chlorosis strains of Xylella fastidiosa. J Bacteriol 185, 1018-1026 (February 2003).

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