For the first time, scientists have reported mapping the genes of a plant disease, an advance that could lead to new approaches to fighting a bacterial scourge that ravages orange groves and other crops.
The work also sheds light on the way bacteria infect both humans and plants and thwart their defenses.
"This sort of information is going to open up crop protection strategies the way genome sequencing is opening up new pharmaceutical strategies to control infectious diseases" in people, said Charles J. Arntzen, president of the Boyce Thompson Institute at Cornell University.
Sponsored by the State of Sao Paolo Research Foundation in Brazil, 200 scientists in 34 molecular biology labs worked for two years to sequence the genome of the bacteria Xylella fastidiosa.
The scientists reported in Thursday's issue of the journal Nature that they were able to identify the function of 47 percent of the bacteria's 2,904 genes, offering researchers targets for developing cheaper ways of controlling the disease, known as citrus variegated chlorosis, or CVC.
Joao Carlos Setubal, who led the study as coordinator of the Bioinformatics Laboratory at the University of Campinas in Brazil, said the project made Brazil a new force in the international genome arena, after starting from a position of practically no local expertise.
The scientists also reported finding at least 83 genes in Xylella fastidiosa that came from other bacteria, including some that help fight off a plant's natural defenses.
"This is the strongest story we have had in the plant biology area or non-human medicine for gene transfer across bacteria," Arntzen said. It gives scientists a better understanding of how germs and evolve along with the plants they infect, he said.
The finding also sheds light on how bacteria that cause human diseases develop resistance to antibiotics, he added.
"It really is fascinating to see how many similarities there are between plant and human pathogens," Arntzen said. "That is what is coming out of a lot of genome sequencing. We can study one organism and learn something about another one."
Carried by insects called sharpshooter leafhoppers, the bacteria infest the xylem, the tubes under the bark of a tree that transport water. By blocking water absorption, the disease causes the fruit to be small, hard and commercially worthless. Related strains of the bacteria attack coffee, almonds, pecans, grapevines, alfalfa, peaches and other plants.
The disease was first identified in Brazil in 1987 and causes $50 million a year in damage to orange groves there, which produce half the orange juice concentrate in the world, Setubal said.
The strain of bacteria was chosen for the genome project because it is expensive to combat with current means, which include insecticides, pruning and replacing trees.
With this new knowledge of the genetic processes in the bacteria, it may be possible to create a simple drug that would either kill it or make it harmless to the plant, he added.
Though 23 other bacteria genomes have been mapped, this marks the first time scientists have publicly reported sequencing a free-living type of bacteria that causes disease in plants, Michael Bevan of the John Innes Centre in England wrote in an accompanying editorial.
"With the importance of plant pathogens limiting our food supply, it is really quite shocking that this is the first time a complete genome sequence has been produced," Arntzen said. "When you consider how many human pathogens have been completely sequenced, it tells us where we put our
priorities in terms of research investment."
by Associated Press