Some scientists and policy decision-makers have proposed that genetic engineering (GE), a modern form of crop modification, will help create a new generation of plants that will dramatically reduce our dependence on pesticides, enhance the health of our agricultural systems, and increase the nutritional content of food. They believe GE will be a dramatic step forward that will topple decades of criticism about the dangerous overuse of pesticides and toxic herbicides, leading us to a more ecological way of farming.

Or will it? While the public has generally accepted the application of GE for the production of new medicines, some consumers indicate grave unease over the consumption and production of GE food, viewing it as unnatural, potentially unsafe to eat and environmentally disruptive. Of these skeptics, the organic farming community has been particularly vocal in its criticism. Some consumers believe that because organic farmers have learned how to produce healthy nutritious food, GE plants are not needed.

Definition:

GE is not a farming method. It is a modern form of crop modification that differs from plant breeding in two basic ways:

1. Plant breeding allows gene transfer only between closely related species. With genetic engineering, genes from the same species or from any other species, even those from animals, can be introduced into a plant. Therefore genetic engineering creates a vast potential for crop alteration.

2. Plant breeding mixes large sets of genes of unknown function, whereas
genetic engineering generally introduces only one to a few well-characterized genes at a time.

History:
For thousands of years, farmers have deliberately selected and improved plants with desired characteristics from wild and cultivated plants.

For example, 10,000 years ago farmers in ancient Mesopotamia developed a hybrid between wild species of wheat and cultivated wheat that became the ancestor of our modern bread wheat. Today breeders manipulate plant species to create desired combinations of traits for specific purposes. In rice and corn, this artificial selection process is generally carried out using pollination. In this process the breeder transfers the male pollen grains to the female part of the flower.

Using these techniques, breeders have been highly successful in developing new varieties; so successful in fact that corn varieties only faintly resemble their predecessors and survive only in human-made environments.

Today, all of our principal food crops come from domesticated varieties. As with breeding, the goal of genetic engineering is to alter the genetic makeup of the crop.

The Process of plant genetic engineering
There are a couple of ways to genetically engineer a plant. One method is to use particle bombardment, or biolistics. In this process, millions of DNA-coated metal particles are shot at target cells or tissues using a biolistic device or gene gun. The DNA elutes off the particles that lodge inside the cells, and a portion may be stably incorporated in the host chromosomes.

Another method is called “Agrobacterium-mediated” transformation. For rice, the starting material is an immature and still doughy seed, which carries the precious embryo and the genetic material within. If left to mature, the embryo would become edible grain.

A quick dip in ethanol, followed by a soak in bleach and a spray of sterile water will protect the rice embryo from contaminants in the air—bacteria and fungi that are harmless to humans but can kill the delicate rice cells. The hulled grains are placed onto a freshly prepared plate carrying nutrients that will nourish the embryo and moved to a growth chamber that will supply adequate light and heat.

In about two weeks, the grain will grow into a glistening mass called a “callus,” a sort of stem cell open to direction, not yet having decided whether to develop into a particular organ, such as a leaf or root. The new callus is separated from the grain with tweezers. The next step is to introduce a new gene into the cells of the rice callus; to do this scientists rely on a soil bacterium called Agrobacterium. This bacterium can do something that virtually no other organism can do; it can form a bridge to the plant cell and then transfer some of its own genes across the plant cell wall, then across the membrane and into the nucleus.

This ancient process, known to biologists for a century, was only understood in detail over the last thirty years. It is now known that this gene transfer “transforms” the plants into food production units for the bacteria. You can tell if a plant is infected by the appearance of large tumors at the base of the plant. Sometimes the results are dramatic—one of the oak trees on the UC Davis campus has a crown gall tumor the size of a small car.

Biologists, faithful to their long tradition of manipulation and exploitation, have cleverly removed the bacterial genes that cause the tumor so that the bacteria can infect without disrupting plant growth. They have also figured out that it is possible to replace some of the bacterial genes with genes from other species. The bacteria, unaware that the genes have been swapped, will deliver the new genes into the plant. To carry out this subterfuge, biologists employ other tools of our trade: restriction enzymes that act like tiny scissors to cut out the bacterial genes and ligases that act like glue to insert the new genes into the genome of Agrobacterium.

This cutting and pasting method is used to introduce genes-of-interest, say a resistance gene or stress tolerance gene into Agrobacterium. The callus can then be dipped into a broth containing the engineered bacteria. At this point, the bacterium acts like a courier delivering the gene-of-interest into the genome of the cultivated rice species. The bacteria must first identify its target, then infect the cell, transfer its DNA across the rice cell membrane into the nucleus, and finally into DNA that is bundled into chromosomes in each nucleus. In nature and in the lab, the bacteria do the work of gene delivery.

Scientists cannot predict where the new gene will land beforehand, although it is straightforward to determine the location of the new gene after it is integrated into the crop DNA. Sometimes the gene will land in a spot that disrupts a critical function of the rice cell, in which case that cell will no longer grow. In most cases, however, the transformed cell will thrive and reproduce carrying a new bit of genetic material along with it.

How unnatural is this? If we insert genes into random sites in a genome, won’t we destabilize a structure that has evolved over millions of years? It turns out that plant genomes are used to this kind of abuse. It is now well documented that rice and other organisms contain pieces of DNA that move around (called transposable elements) in a seemingly erratic fashion. Not only do they insert themselves into new places, but sometimes they pick up pieces of other genes and take those fragments along for the ride as well. For example, a recent study showed that in the rice genome there are over 3000 of these pieces of DNA-containing fragments, called pack mules, from more than 1000 genes (Jiang et al. 2004). Sometimes several fragments are picked up from different genes, rearranged, fused, and then expressed as new proteins. By looking at the genome sequences, we also now know that plants have acquired genes from many different organisms. It seems then that the genetic engineering process we carry out in the lab has certain similarities to that which occurs in nature.

Not all of the bacteria will be successful in transferring their DNA to the cell; only a very few of the rice cells will receive the new gene and be “transformed.” How then does the biologist distinguish the genetically engineered cell from the thousands of rice cells lacking the genes? In fact, this would not be possible without another tool, called the marker gene. In early experiments of plant transformation, the commonly used marker was a gene that encoded resistance to an antibiotic. In this process, not only is the new gene transferred to the cell, but the marker gene is as well. Today, other markers are available, such as those that allow the transformed plant to grow on high levels of particular sugars; in essence this marker is a sugar enablement gene that allows it to grow on sugars it cannot otherwise use. By placing the infected rice cells on the “selection” (sugar or antibiotic) media only the transformed cells will survive, inhibiting growth of the rest of the plant cells. In other words, the marker genes bestow properties of survival only to those cells that are genetically engineered, allowing biologists to pluck the newly transformed cells from a lawn of dying, untransformed cells.

In two more weeks the newly transformed cells will give rise to new cells carrying the marker gene and the gene-of-interest. These new cells appear as tiny clumps of whitish, nearly translucent globs about the size of small beads. These cells are genetically identical to the starting material (the rice seed), except that they also possess the desired gene-of-interest and the marker gene. Once transferred to nutrient plates containing plant hormones, the cells will produce roots and shoots. The GE seedlings can be transplanted into soil-filled pots. They will reproduce and produce seed like any other rice plant.

Today, one billion acres of GE crops have been grown; hundreds of millions of people have eaten GE food for more than a decade without a single verifiable case of adverse side effects to the environment or to human health. Still, GE provokes controversy, and, sometimes, violent protests.

Potential for using GE to boost crop yields

One way to boost yields is to develop crops that can survive harsh conditions such as drought, cold, heat, salt, and flooding. Many of the world’s poorest people farm in areas that are far from ideal, and freshwater sources are decreasing in quantity and quality throughout the world. New crop varieties designed to survive in difficult environments will have a significant human and ecological impact. In the future this is where genetic engineering will likely play an important role. Crops with enhanced tolerance to drought, for instance, would allow farmers to produce more food using less water. Already there are varieties of genetically engineered wheat that can tolerate drought, as well as rice that can tolerate flooding and tomato plants that can tolerate salt.
Another important challenge is to fight pests and disease, which take an estimated 20 to 40 percent bite out of agricultural productivity worldwide. Reducing this loss would be equivalent to creating more land and more water. But current pesticide use is a health and environmental hazard, and organic and genetic engineering offer complementary solutions. Genetic engineering can be used to develop seeds with enhanced resistance to pests and pathogens; organic farming can manage the overall spectrum of pests more effectively. Genetically engineered crops have already enjoyed major success against pests. For example, on farm field trials carried out in central and southern India, where small-scale farmers typically suffer large losses because of pests, average yields of genetically engineered crops exceeded those of conventional crops by 80 percent. In Hawaii, the 1998 introduction of an engineered papaya plant that could resist the papaya ringspot virus virtually saved the industry. There was no organic approach available then to protect the papaya from this devastating disease, nor is there now.

Genetic engineering can also help achieve other goals of the ecological farming movement. By reducing the use of pesticides and by reducing pests and disease, it can make farming more affordable and thus keep family farmers in business and assure local food security. It can also make food more nutritious: In 2011, plant breeders expect to release “golden rice,” a genetically engineered variety that will help fight Vitamin A deficiency in the developing world, a disease that contributes to the deaths of hundreds of thousands of young children each year.

Opposition to GE crops
To many people, genetically altering crops feels fundamentally wrong or unnatural. They believe that farmers already have enough tools for a productive and healthy farming system.

On an environmental level, many worry that genetically engineered crops will cross-pollinate nearby species to create a new kind of weed that could invade pristine ecosystems and destroy native plant populations. On a personal level, many consumers worry that genetically engineered foods are unsafe or unhealthy to eat.
So far, however, it appears those concerns are driven more by technological anxiety than by science. Virtually all scientific panels that have studied this matter have concluded that pollen drift from genetically engineered varieties currently grown in the United States does not pose a risk of invasiveness. (Although this does not mean that future crop varieties will also be harmless: each new crop variety must be considered on a case-by-case basis.) And in terms of food safety, a report by the National Academy of Sciences concluded that the process of adding genes to our food by genetic engineering is no riskier than mixing genes by conventional plant breeding.

Today 70 percent of all processed foods in the United States have at least one ingredient from genetically engineered corn, cotton, canola, or soybean. Unlike the well-documented adverse effects of some pesticides, there has not been a single case of illness associated with these crops.

Intellectual property
Many opponents of genetic engineering fear that a blizzard of patents on genetically engineered plants and seeds will put control of agriculture in the hands of a few giant companies that produce the seeds.

Yet there are many new and imaginative methods that businesses and universities are now using to ensure that breakthroughs and useful technologies benefit less developed countries and small-acreage farmers. For example, the nonprofit initiative Public Intellectual Property Resource for Agriculture brings together intellectual property from more than 40 universities, public agencies, and nonprofit institutes and makes these technologies available to developing countries around the world for humanitarian purposes.