For the first time a commercially useful gene has been transplanted and shown to be active in an important corp plant, reports William Hiatt of CAlgene, Inc., a plant biotechnology company in Davis, Calif. After a bacterial gene was introduced into tobacco plants, the plants showed an increased tolerance to the widely used herbicide glyphosate. A problem currently limiting the usefulness of herbicides is that they must distinguish between the crop and the pest — plants that often have biochemical similarities. Thus researches have looked for more and more specific herbicides to kill the pest but spare the crop. But genetic engineering has made more practical another approach–the tailoring of the crop plant to make it less susceptible to a particular herbicide.
The gene that Calgene scientists have transplanted into tobacco originally arose in mutagenized bacteria. A form of the gene aroA, it encodes an enzyme in which one amino acid is different from its natural counterpart. The mutant enzyme has a lower affinity for the herbicide than either the plant or normal bacterial enzyme. In the leaves of tobacco plants containing the transplanted gene, the mutant gene provides 25 percent of the total activity of the enzyme that normally is inhibited by glyphosate. Calgene now plans to extend this work to other crop plants.
According to science team leader Luca Comai, the scientists have already introduced the mutant aroA gene into soybean, tomato and oilseed rape cells in laboratory culture and are currently working on corn cells. Calgene also plans to develop and market glyphosate-tolerant varieties of corn, in collaboration with Phytogen of Pasadena, Calif., and forest trees, in collaboration with the U.S.