Perspectives Online

Irish potato famine pathogen takes gun to knife fight

An international team of researchers – including Dr. Jean Beagle Ristaino, professor of plant pathology at North Carolina State University – has completed the genome sequence of one of the most destructive and rapidly evolving pathogens in the world.

The research shows that Phytophthora infestans, the fungus-like pathogen responsible for the Irish potato famine in the 1840s as well as “late blight” disease currently decimating tomatoes and potatoes across the United States, has a larger and more complex set of genes than previously sequenced cousin Phytophthora genomes. The P. infestans genome – two-and-a-half to four times bigger than its cousins – contains contrasting regions. Some regions are densely packed with genes that don’t seem to change much, while some regions are sparsely populated with genes that seem to change rapidly.

Knowing more about how the pathogen infects plants – including the ways it learns to evade resistance genes specifically employed to halt its progress – and the mechanisms behind its rapid evolution can help scientists devise new ways of protecting plants.

The research is published in the Sept. 10 online edition of Nature.

The genome sequence shows that in the metaphorical “arms race” of pathogens versus their hosts, P. infestans seems to have an upper hand in its interactions with potatoes and tomatoes due to its large number of so-called effector genes. These effector genes – which appear to be located in the large genome’s sparsely populated regions – change quickly and have remarkable success at breaking down a host plant’s defenses, Ristaino says, including plants that have been specifically bred to withstand the pathogen’s attacks.

“The expanded regions appear to give the effector genes the ‘plasticity’ they need to evolve rapidly,” Ristaino says. “That allows them to overcome plant defenses.”

P. infestans is a particularly destructive pathogen that can destroy a field of potatoes or tomatoes within days. There are a number of strains, or types, of P. infestans; Ristaino has spent much of her research career as a “spud sleuth” who has identified the specific strain of the pathogen that caused the Irish potato famine in the 1840s. Her lab is currently working on collecting, archiving and genotyping this year’s outbreaks of late blight disease. Epidemics first occurred in the Southeast in May, but also spread rapidly in the Northeast on home garden tomato plants. NCSU News Services