Scientists Decipher Genome of Irish Potato Famine Pathogen

An international team of scientists has unraveled the genetic code of Phytophthora infestans, the notorious pathogen that triggered the Irish potato famine in the mid-19^th century. The pathogen continues to ravage tomato and potato crops, and costs farmers around the world more than USD 6 billion a year.

Long considered a fungus, Phytophthora is a member of the oomycetes or water molds, which are more related to brown algae and diatoms. The pathogen is remarkable for its ability to change, according to scientists. It can quickly overcome the defenses, for instance, of genetically resistant potatoes that have been painstakingly bred to fend off infection. The genome, published in the journal Nature, provides clue to the tactics employed by P. infestans to rapidly adapt to host plants.

According to the researchers, P. infestans has an expanded genome that is two and a half to four times the size of its relatives' genomes. They also found that repetitive DNA or transposons, genetic elements that can jump around the genome, account for about 75 percent of the entire P. infestans genome. "Such a large amount of repetitive DNA is pretty surprising, since there is a metabolic cost to maintain it," said Chad Nusbaum, leader of the study and researcher at the Broad Institute of Harvard and MIT.

Nusbaum and colleagues believe that carrying this excess of repetitive DNA provides advantage for the pathogen. According to Brian Haas, co-author of the paper and also a researcher at the Broad Institute, "repeat-rich regions change rapidly over time, acting as a kind of incubator to enable the rapid birth and death of genes that are key to plant infection. As a result, these critical genes may be gained and lost so rapidly that the hosts simply can't keep up."

The paper is available at http://dx.doi.org/10.1038/nature08358 For more information, read http://www.harvardscience.harvard.edu/foundations/articles/genome-irish-potato-famine-pathogen-decoded