Irish potato famine caused by crafty germ

By Sheilah Downey - sheilahd at foodconsuemr dot org  

The pathogen that triggered the Irish potato famine, and led to the deaths of 750,000 people, had a two-speed genomic strategy that allowed it to outwit plant hosts, according to a study released today.

"This pathogen has an exquisite ability to adapt and change, and that's what makes it so dangerous," said senior author Chad Nusbaum, of the Genome Sequencing and Analysis Program at the Broad Institute of MIT and Harvard, in a press release. "We now have a comprehensive view of its genome, revealing the unusual properties that drive its remarkable adaptability."

The organism boasts an "unusually large genome size, more than twice that of related species," and is the same one that now threatens many potato and tomato crops across much of the United States, according to the Broad Institute.

Researchers said in addition to its size, the genome has an extraordinary structure which enabled a rapid evolution of genes involved in plant infection. Data from the research exposed a mechanism that enables the pathogen to outsmart its plant hosts but may help researchers find a way to control it.

"Our findings suggest a two-speed genome, meaning that different parts of the genome are evolving at different rates," said co-lead author Sophien Kamoun, head of the Sainsbury Laboratory in Norwich, UK. "Future sequencing of additional strains and close relatives of this pathogen will help test this hypothesis and could transform our understanding of how it adapts to immune plants."

The organism responsible for the potato famine was called the Phytophthora infestans. Once considered a fungus, it is now known as a member of the "water molds," more closely related to a malaria parasite.

The parasite thrives in cool, wet weather causing a late blight disease that can decimate entire fields in just days.

Remarkably, the pathogen can quickly adapt to new plant hosts and attack even genetically resistant potatoes that have been bred to fend off infection, researchers said.

Nusbaum and colleagues determined that the massive size of the genome stemmed from "junk DNA," or repetitive DNA, which made up 75 percent of the genome.

The potato famine struck Ireland from 1845 to 1947 and left 750,000 people dead of starvation or disease. Hundreds of thousands more left the country.

Findings of the research were published in the Sept. 9 online issue of the journal Nature.