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
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.