...and virus-resistant genes appear.

Scientists have boosted the ability of plants to ward off single viruses by giving them powerful foreign genes. Now, researchers say they are engineering plants to resist multiple viruses.

A Japanese team has inserted into tobacco plants human genes that express two enzymes that together kill common crop viruses and their host cells, report Toshiya Ogawa and his colleagues at Kirin Brewery's Central Laboratory for Key Technology in Yokohama.

The enzymes, 2',5'-oligoadenylate synthetase and ribonuclease L, target RNA viruses (SN: 6/15/96, p. 381), plants' main viral enemies, the scientists report in the November Nature Biotechnology. These enzymes also guard against viral infections in mammals.

Earlier this year, a team at the Cleveland Clinic Research Institute in Ohio carried out a similar experiment. Together, the groups have demonstrated that the enzymes have "a substantial impact on the replication and accumulation of viruses that belong to four different taxonomic groups and likely will have similar effects on other viruses," Roger N. Beachy of the Scripps Research Institute in La Jolla, Calif., notes in an accompanying article. The viruses commonly attack cucumbers, tomatoes, tobacco, and other crops.

The engineered plants aren't immune to infection, but they resist it well enough to control the spread of the virus, Ogawa and his colleagues assert. They plan to test the technique on chrysanthemums and carnations in the field in the near future, says coauthor Isao Ishida. The researchers plan to use similar enzymes obtained from cows, not humans.