Scientists at UC Riverside in California have discovered the genetic trigger for the Great Potato Famine in phytophthora, a genus of molds that infest potatoes, soybeans, tomatoes and avocados. It was known that phytopthora caused the potato rot but not how it took hold.

According to U-T San Diego,  microbes  in phytopthora shut down the defense system these plants use to repel infections, a process called RNA silencing, which uses fragments of RNA called "small RNAs" to suppress the activity of certain genes. Without RNA silencing the potato is open to attack.

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According to a new study, proteins made by Phytophthora called "effectors" block RNA silencing in these plants, reducing their immunity to infection and making them vulnerable,.

During the Great Potato Famine in the mid-19th century, Phytophthora infestans destroyed the potato leaves and tubers in Ireland. One million Irish died of starvation during the famine and many of the survivors emigrated to the U.S.

The molds still threaten agriculture crops, with billions of dollars lost worldwide.

RNA silencing is also found in humans and mammals and similar effectors are made by the Plasmodium genus of malarial parasites.

The study, which was published by Nature Genetics, was led by Wenbo Ma, a UCR associate professor of plant pathology and microbiology. In the study, researchers alluded to the larger implication of their research.

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"Our discovery warrants further efforts to identify and characterize RNA silencing suppressors produced by eukaryotic pathogens that infect mammals."

The researchers are already studying how to thwart the effectors, which could lead to the development of Phytopthera-resistant crops.

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"We are in the process of testing some plants to manipulate the RNA silencing pathway, and then infect them with Phytopthera pathogens to see whether there's enhanced resistance or enhanced susceptability," Ma said.

If their work is successful, the technology can be used to produce crop plants resistant to the various species of Phytopthora.