Brazil Scientists Help Calfornia Wine

A scientific team from Brazil has cracked the genetic code for a bacterial menace that causes Pierce's disease in grapevines, one of the most serious threats facing the California wine industry. Despite various attempts to halt the disease, which is spread by the eating habits of the glassy-winged sharpshooter, the parasite known as Xylella fastidiosa continues to decimate vineyards throughout California, causing upwards of $40 million in damages so far.

The complete blueprint of the bacteria's DNA, published in the February issue of the Journal of Bacteriology, provides important insights on how the pest may one day be brought under control.

"To restrict the development of a plant pathogen you need to know how the disease is established," said the lead author of the study, Dr. Marie-Anne Van Sluys, who is with the Department of Botany at the University of Sao Paulo. "The genetic sequence of Xylella may help us attack this pathogen without harming other bacteria that plants need to survive."

Xylella is a particularly damaging bacterium that grows in the gut of small winged insects, which then spread the disease when they feed off plants. Once infected, the leaves' water supply gets cut off, causing the plant to wither and die.

Two years ago, Brazilian scientists created a stir by genetically sequencing a strain of Xylella that causes a similar disease in citrus groves, the first time a bacterial plant pathogen had ever been decoded. Xylella, which harms a large variety of crops--including fruits, nuts, and coffee, among others--has left a trail of destruction from California to Argentina.

With two different strains to compare, scientists now have a better chance to combat the pest. The Brazil team found that the citrus and grapevine Xylella organisms share identical metabolic functions and it seems likely that they both use the same set of genes to destroy plants.

"The two Xylella strains are very similar genetically," said Dr. Van Sluys. "We suspect that they use the same strategy to colonize the plant vessels, and if we can identify a common mechanism, it might be possible to use one strategy to combat both diseases."

Already, lab experiments demonstrate that Xylella's relatively small genome is ill-equipped to take advantage of a nutrient-rich environment, with the bacteria preferring a constant source of the same nutrients, rather than any additional ones. As the name implies, Xylella fastidiosa appears highly fastidious about what it infects, suggesting that simply changing how crops are planted could offer one possible route for fighting the disease.

On the genetic front, Xylella possesses complex proteins that can repair damaged DNA, the same mechanism that seemingly allows Salmonella to turn more virulent. The two Xylella strains also have distinct genomic islands, areas where genes are transferred so that an organism can adapt to its environment and evolve.

Although the functions of these genomic islands are not yet clear, they may represent another opportunity to defeat the pest. All told, the complete genome of Xylella adds to a growing list of scientific findings that may help California wine growers, as well as many other farmers throughout the world.

"This is a good example of how scientists from developing and advanced countries can work together to solve mutual problems," said Dr. Andrew Simpson of the Ludwig Institute for Cancer Research, who helped coordinate the Xylella genomic program in Brazil.

The Ludwig Institute, along with the Sao Paulo scientific foundation FAPSEP, initiated the first Xylella genome project in Brazil in 1997. This pioneering work led to funding from the United States Department of Agriculture (USDA), the American Vineyard Foundation, and the California Department of Food and Agriculture to sequence the strain of Xylella found in California. (The DNA of the California strain of Xylella was provided by the USDA's Agricultural Research Service.)

The Ludwig Institute for Cancer Research is an international not-for-profit organization that originates and conducts long-term research programs directed to the ultimate goal of controlling cancer. With little genetic research experience before, Brazil is now considered a world leader in both plant and cancer genomics.

Note to Editors: A fact sheet on the importance of supporting science in developing countries can be found on the Ludwig Institute's Web site (www.licr.org) at: http://www.licr.org/07_spot/012903_genomics.htm