Researchers uncover how infections combat plant immune responses

Researchers at the University of California, Riverside, with colleagues at the University of Florida and at UC Davis, have uncovered how viruses circumvent the immune response of plants.

The findings were published in the Nov. 2 issue of the Proceedings of the National Academy of Sciences in a paper titled "Three Distinct Suppressors of RNA Silencing Encoded By a 20-kb Viral RNA Genome." UC Riverside Associate Professor of Plant Pathology Shou-Wei Ding, at the Center for Plant Cell Biology, and UCR colleagues Rui Lu, Wan-Xiang Li and Michael Shintaku, co-authored the paper with Bryce W. Falk at UC Davis and William O. Dawson at the University of Florida Citrus Research and Education Center.

RNA silencing is a recently discovered defense mechanism against virus infection in plants and invertebrates. For successful infection to occur, viruses must be able to suppress the RNA silencing's antiviral response.

"Our results demonstrate that citrus tristeza virus (CTV) produces three proteins that are suppressors of RNA silencing and each inhibits RNA silencing in a distinct manner," said Ding.

CTV is one of the most important virus pathogens affecting citrus worldwide, causing significant economic losses not only from disease, but also from the need to remove CTV-infected trees. Since viral suppressors are also known to interfere with plant development, further analyses of the CTV suppressors will explain why CTV is capable of such destructive effects. One approach for the control of CTV in a number of labs is to genetically engineer virus-resistant citrus trees.

"Our findings will help improving the efficacy of this approach, e.g., by directly targeting the CTV suppressor genes," Ding said.

"Our work indicates for the first time that viruses may have to produce more than one suppressor of RNA silencing to overcome the antiviral immunity," he added. "Secondly, one of the CTV suppressors identified is mechanistically novel as it inhibits spread of RNA silencing without interfering with intracellular RNA silencing."

As a result, that type of suppressor cannot be identified by the methods in wide use today by labs around the world.

The California Citrus Research Board, the UC-Biostar program and the U.S. Department of Agriculture funded the research.

---

---