GENETIC ENGINEERING OF PLANTS
The first step in genetically engineering a plant is to identify a gene that will confer a specific desirable trait on the plant. In some ways, this is the hardest part of genetic engineering. The most desirable traits for a crop are increases in the amount of seed, grain, or other plant products. Increased resistance to disease or drought is also very useful. Finding the genes responsible is difficult, because multiple interacting genes usually control such traits. In addition, such genes may play other roles in plant physiology or development.
So far, most successful genetic engineering of plants has relied on inserting one or a few genes that supply simple, yet useful, properties. For example, resistance to the herbicide glyphosate is due to a single gene. Making a crop such as soybean resistant to glyphosate allows the farmer to kill the weeds in the field without harming the soybeans (see later discussion). Another desirable trait often due to a single gene is the production of toxins that kill harmful insects (see later discussion). Both these cases rely on transgenes derived from bacteria. As more research into plant physiology occurs, more genes can be identified that increase the value of a crop. For example, a two-gene pathway was engineered into rice to make it more resistant to drought (see later discussion).
Plants can also be engineered for novel products. Thus, golden rice expresses the biosynthetic pathway for vitamin A precursors. This rice was developed for people who rely on rice as the one main food in their diet. The addition of vitamin A precursors can prevent deficiencies that cause blindness or premature death in children in developing countries. Researchers have also engineered the human insulin gene for expression in Arabidopsis and safflower.
At present, insulin is produced by engineered bacteria. However, plant-produced insulin is easier to isolate and purify in bulk and should cost much less. Further research will identify new genes and useful pathways that can be engineered into plants. Perhaps engineered plants will be used to clean up oil spills or other pollutants by growing them on contaminated soil.