Plant pathologists will be getting their first look at the complete genome of two species of Phytophthora, a funguslike pathogen that harms a wide array of plants. On 10 June, sequencers unveiled the genome of Phytophthora ramorum, the cause of sudden oak death, and also of Phytophthora sojae, which rots the roots of soybeans. The new sequences should provide insights into basic tricks of the pathogens and could provide new tools in the fight against sudden oak death, which has been spreading across the country (Science, 26 March, p. 1959).
The nearly $4 million effort, funded by the U.S. Department of Energy, the U.S. Department of Agriculture, and the National Science Foundation, began in 2002 and was carried out by DOE's Joint Genome Institute in Walnut Creek, California, and the Virginia Bioinformatics Institute (VBI) in Blacksburg. P. sojae was chosen because it's well studied and has a relatively compact genome. It turned out to be 95 megabases long, while P. ramorum, discovered only in 2000, was an even smaller 65 megabases.
VBI's Brett Tyler says that similarities between the two species tend to break down in regions that contain host-specific genes, suggesting extensive specialization. Another initial finding is that genes for proteins used to attack plant defenses are particularly abundant. "They seem to be undergoing very rapid evolution," Tyler says.
The sequence will help researchers find out much more about how the pathogen and its hosts interact, and that could lead to disease-resistant plants, says Chuanxue Hong, a plant pathologist at Virginia Tech's Agricultural Research and Extension Center in Virginia Beach. "In the long term, [the genomes] will be very significant," Hong says.
The most immediate payoff of the genome will be better ways to identify and track P. ramorum, and new tests could be available within a year, Tyler predicts. The genome will also help determine whether the two mating types of P. ramorum are sexually active in North America, which would raise the specter of increased virulence and greater host ranges, says Matteo Garbelotto of the University of California, Berkeley, whose lab provided the pathogen for sequencing. "We'll really be able to nail down the biology of the organism." He adds that new detection methods, based on a plant's response to Phytophthora's attack proteins, would also greatly simplify testing.