X.S. Ding, Yi Li and Rick Nelson looking at rice plants infected with Brome mosaic virus.

Dr. Yi Li of Peking University in Beijing, China, recently completed a multi-year collaborative project with Rick Nelson's lab in which the researchers studied the molecular and cell biology of Rice dwarf virus (RDV). Li became interested in working with the Foundation after learning of the confocal microscopy work done here to study the cell-to-cell movement of plant viruses. Funding for the project came from a Rockefeller Foundation grant to Li, which was administered by the Noble Foundation. The grant allowed Li to spend extended periods of time working at the Foundation's campus in Ardmore.

RDV, which is spread by insects, is one of the most economically damaging viruses of rice in southern Asia. It is a member of the genus Phytoreovirus, which consists of viruses with segmented double-stranded RNA genomes. This type of virus is difficult to manipulate because of its structure.

During the initial work of the collaboration, researchers sought to understand how RDV moved from cell to cell in plants, because that movement is required for the systemic infection of the plant to take place. Using clones of RDV's 12 separate segments of double-stranded RNA, they analyzed the proteins produced by each segment for their ability to help a virus defective in cell-to-cell movement, Potato virus X (PVX), move through the plant Nicotiana benthamiana, a relative of tobacco and a favorite host for viruses. Out of the 12, only the protein produced by segment 6 (S6) restored the cell-to-cell movement of PVX. In addition, the protein produced by S6 in infected rice was located in the tunnels, called plasmodesmata, that connect plant cells and are the route viruses use to move between cells.

So, through the collaboration, a previously unknown protein encoded by RDV that supports virus movement was identified. A paper detailing the findings was published in the May 2004 issue of Journal of Virology.

The work in conjunction with Li has been expanded to look for plant proteins that interact with RDV proteins, using Li's host proteins and the Noble Foundation's Brome mosaic virus (BMV) vector to determine the host proteins' functions. The technique, called virus-induced gene silencing (VIGS), to date has not been used to study gene function in rice because no rice-infecting virus amenable to the procedure was known. As part of a collaboration with Forage Improvement Division personnel (Rouf Mian and John Zwonitzer), Xin Shun Ding in Nelson's lab cloned and altered a fescue- and rice-infecting Brome mosaic virus strain, F-BMV, for use as a vector during VIGS studies.

"The collaborative work with Dr. Li has yielded novel and important findings about the method RDV uses to move cell to cell in plants," Nelson said. "With this information, it is now possible to study host factors that interact with the S6 protein from RDV and to devise schemes to prevent virus movement, leading to virus-resistant plants.

"It is great that we are able to utilize another technology developed here at the Foundation, namely the use of our Brome mosaic virus vector to study host protein functions, to help in Dr. Li's studies," he said. "The information obtained through this continuing interaction could have significant importance for those growing grasses for forage or grain.

"We thank the Rockefeller Foundation for the seed money that allowed this collaboration to occur."