When a pathogen attacks a plant, infection usually follows after the plant’s immune system is compromised. A team of researchers at the University of California, Riverside focused on Phytophthora, the pathogen that triggered the Irish Famine of the 19th century, and deciphered how it succeeded in crippling the potato plant’s immune system.

The genus Phytophthora contains many notorious pathogens of crops. Phytophthora pathogens cause worldwide losses of more than $6 billion each year on potato (Phytophthora infestans) and about $2 billion each year on soybean (Phytophthora sojae).

The researchers, led by Wenbo Ma, an associate professor of plant pathology and microbiology, focused their attention on a class of essential virulence proteins produced by a broad range of pathogens, including Phytophthora, called “effectors.” The effectors are delivered to, and function only in, the cells of the host plants the pathogens attack. The researchers found that Phytophthora effectors blocked the RNA silencing pathways in their host plants (such as potato, tomato and soybean), resulting first in a suppression of host immunity and thereafter in an increase in the plants’ susceptibility to disease.

“Phytophthora has evolved a way to break the immunity of its host plants,” Ma explained. “Its effectors are the first example of proteins produced by eukaryotic pathogens—nucleated single- or multi-cellular organisms—that promote infection by suppressing the host RNA silencing process. Our work shows that RNA silencing suppression is a common strategy used by a variety of pathogens—viruses, bacteria and Phytophthora—to cause disease, and shows, too, that RNA silencing is an important battleground during infection by pathogens across kingdoms.”
 
Study results appeared online Feb. 3 in Nature Genetics.
 
Ma was joined in the study by UC Riverside’s Yongli Qiao, Lin Liu, Cristina Flores, James Wong, Jinxia Shi, Xianbing Wang, Xigang Liu, Qijun Xiang, Shushu Jiang, Howard S. Judelson and Xuemei Chen; Fuchun Zhang at Xinjiang University, China; and Qin Xiong and Yuanchao Wang at Nanjing Agricultural University, China.

SOURCE: University of California