Keeping Genes Out of Pollen

Researchers have found a way to stick a gene into tobacco plants that protects them against a herbicide, with little risk of the foreign gene spreading to neighboring weeds. The technique, reported in the April issue of Nature Biotechnology, could be a boon for farmers who want to plant transgenic crops.

Protecting crops in this way would allow farmers to kill weeds more effectively. Earlier attempts to achieve this feat through genetic engineering relied on injecting foreign DNA into the nuclei of plant cells. But these genes end up in pollen, which may somehow cross-fertilize weeds. Henry Daniell, a microbiologist at Auburn University in Alabama, realized that there could be an alternative way to introduce foreign genes into plants: through their chloroplasts, organelles that act like tiny solar panels and have their own DNA. In many species, including tobacco, chloroplast DNA is not passed on during pollination, which means that new genes are far less likely to migrate to other species.

Daniell and his colleagues took a petunia's gene for EPSPS, a naturally occurring enzyme that inhibits the potent herbicide glyphosate. They shot the gene into tobacco chloroplasts with a "gene gun," which blasts DNA into cells with pressurized gas, then collected and planted the seeds. When they tested the doctored plants more than 4 months later, the researchers found a 10-fold increase in resistance to the toxic effects of glyphosate. Daniell attributes this high degree of protection to the huge number of EPSPS genes expressed in the engineered plants.

Applying the new method to maize, sunflower, soybean, and other staples grown in large fields vulnerable to weeds would be a significant boon for farmers looking to kill weeds but preserve crops, says Peter Bretting, a biologist with the USDA's Agricultural Research Service in Ames, Iowa. On the other hand, Bretting cautions, some plants--such as pines and alfalfa--do transmit chloroplasts in pollen and therefore would not be likely candidates for this approach.