Turning a Rice Virus Against Itself

The rice yellow mottle virus (RYMV), endemic in Africa, can destroy just about every plant in a field. Although native African rice strains are resistant to the virus, it can wreak havoc in fields of higher yielding varieties imported from Asia, which have no natural resistance. Because resistance depends on several genes and it's difficult to cross the African and Asian varieties, no one has been able to introduce RYMV resistance through traditional breeding. But in the current issue of Nature Biotechnology, researchers describe a way to defeat the virus using its own genes.

Several research teams have shown that inserting a viral gene into a plant's DNA gives the plant a kind of immunity to the virus. Although no one yet understands the exact mechanism, researchers suspect that a plant carrying the viral gene somehow recognizes the same gene when the virus invades. It then seems to degrade the gene's RNA transcript, preventing the virus from growing.

Plant geneticist David Baulcombe of the John Innes Center in Norwich, U.K., and his colleagues took RYMV's replicase gene--which allows the virus to make copies of itself--and inserted it into a strain of virus-susceptible rice. The resulting strains had varying degrees of resistance to the strain of virus that donated the gene, but several withstood the virus almost completely. They were even resistant to a variety of other RYMV strains. The resistance lasted through at least three generations.

Most African countries do not yet have regulations governing the introduction of transgenic organisms, and the researchers are waiting until regulations are in place before they conduct field trials. But molecular biologist Roger Beachy of the Donald Danforth Plant Science Center in St. Louis says the initial success offers hope for fighting what the West African Rice Development Association has called one of its top concerns. "Having a single gene ... that will give resistance is quite important," he says. "Right now, there is no other solution."