Analysis of RNA role in spreading disease advances study of damaging plant ...(e of the journal The Plant Cell. Abo...)

About 30 species of viroids exist, affecting such plants as tomatoes, potatoes, palm trees and chrysanthemums. One type of viroid has been known to kill millions of palm trees, but more typical effects of the infection are low plant quality and reduced crop yield. The current way to treat viroids is to harvest and destroy infected crops and start over with new plants.

The effects of viroid infection were first noticed in the 1920s but the cause remained unknown until 1971.

The scientist who discovered the first viroid spent many years trying to find the pathogen, Ding said. Its not bacteria. Its not a virus. It is really its own kind of pathogen. It doesnt make any proteins or have any protein coat. Its just a piece of RNA.

Unlike the better-known DNA structure a double helix with base pairs of nucleotides connecting the strands many RNAs are formed by a single strand that folds back in on itself. As a result, the RNA structure has a series of loops that scientists have long assumed were empty holes with unclear roles in the RNA function.

Research from several labs has recently shown that many of those loops are not holes, but are actually the most important structural parts of the RNA.

Those loops interact with proteins, other RNAs and small molecules. That helped us decide to look at all of the loops of a viroid RNA and see how each one functions, Ding said.

The viroid model used for this research is called the Potato spindle tuber viroid, and its infection was studied in a tobacco-like plant called Nicotiana benthamiana for the experiment. Lead study author Xuehua Zhong, at the time a graduate student and now a postdoctoral researcher at Ohio State, led the work to introduce mutations to each of the 27 loops in this viroid to disrupt its structure and see how that disruption affected either viroid replication or the viroids ability to spread, or both actions in the
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