Engineered Plants May Spread Genes To Weeds
Nature magazine (U.K.) Sept. 3, 1998
Crops engineered to contain genes that give them resistance to pests or
the ability to produce lots of seeds, could pass these genes to their weedier
cousins producing hybrid strains of super-weeds, says Joy Bergelson, assistant
professor of ecology and evolution at the University of Chicago. Her findings
will be reported in the September 3 correspondence pages of Nature.
Artificially created plants, like wild plants, can breed with closely
related species to produce hybrids in what is called out-crossing. For
example, corn, which is a grass, can cross with timothy grass, an abundant
weed. If the corn contains a gene that confers resistance to a pesticide, the
resultant "weedy" hybrid may become a pesticide-resistant nuisance that can
compete with crops for water and nutrients.
Farmers haven't worried about outcrossing because most crop plants are
self-fertilizing, so their genes were considered unlikely to migrate to other
species. But Bergelson has demonstrated that plants thought to be "selfing"
can outcross with closely related species, and that the rate of outcrossing
appears to be enhanced by the fact that they are transgenic.
To test the frequency of outcrossing in transgenic plants, Bergelson grew
three different kinds of Arabidopsis, a selfing mustard plant, and planted
them together on a plot in central Illinois. One type contained a point
mutation in the Csr1-1 gene making it resistant to chlorsulfuron, an
herbicide. The second variety of Arabidopsis was engineered with a mutated
Csr1-1 gene, producing a transgenic chlorsulfuron-resistant plant. The third
type were wild-type Arabidopsis with normal copies of the Csr1-1gene.
The plants were left alone, and their seeds were collected at the season's
end. Plants grown from the seeds were tested for resistance to chlorsulfuron.
Resistant plants were further tested to determine if they inherited the
resistance gene from Crs1-1 mutants or from the transgenic plants containing
the implanted Csr1-1 mutant gene.
Bergelson found that twenty times as many resistant progeny received their
resistance from the transgenic plants as from the mutant plants. "It is
unclear why the transgenic plants had such an abnormally high incidence of out
crossing," says Bergelson, "but the results demonstrate that genetic
engineering can substantially increase the incidence of outcrossing in a
She warns that the widespread use of transgenic crops may directly cause the
creation of weeds with traits intended to increase the fitness of crops,
spurring a need for new pesticides.
Contact: Sharon Parmet
University of Chicago Medical Center