Genome of Irish potato famine pathog...(toes and other related plants causing a ...)

Not only swift in its destruction, the pathogen is also remarkable in its ability to change. For example, it can quickly adapt to new plant hosts, attacking even genetically resistant potatoes that have been painstakingly bred to fend off P. infestans infection. How the pathogen can adapt so rapidly to these immune potatoes has long puzzled scientists.

To understand the genetic basis for the pathogen's adaptive success, the researchers, led by scientists at the Broad Institute and the Sainsbury Laboratory, decoded the P. infestans genome. They produced a high-quality genome sequence and compared it to the genomes of two relatives: P. sojae, which infects soybeans, and P. ramorum, which prefers oak and other trees and causes a condition known as sudden oak death.

One of the most striking findings to emerge from these comparisons is the expanded nature of the P. infestans genetic blueprint: It is two and a half to four times the size of its relatives' genomes.

But perhaps even more surprising than the genome's large size is the source of its added bulk. Nusbaum and his colleagues determined that the additional genomic real estate does not reflect more genes per se, but instead stems from a massive expansion in the amount of repetitive (once considered to be "junk") DNA. In fact, this type of DNA accounts for about 75% 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 Nusbaum. "As a genome biologist, I have to wonder how the organism benefits from having it."

The researchers gained some key insights into the potential advantages of carrying this glut of repetitive DNA by probing its genomic structure. They made three critical observations:

• The P. infesta
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