The real promise of plant genetic engineering
In the last decade the United States has undergone a revolution in agriculture. Genetically modified crops of corn, cotton, and soybeans are now commonplace -- in 1999, over half of the 72 million acres planted with soybeans in the United States were planted with seeds genetically modified to be herbicide resistant, with the result that less tillage has been needed, and as a consequence soil erosion has been greatly lessened. These benefits, while significant, have been largely confined to farmers, making their cultivation of crops cheaper and more efficient. The food that the public gets is the same, it just costs less to get it to the table.
Like the first act of a play, these developments have served mainly to set the stage for the real action, which is only now beginning to happen. With Monday's ground-breaking for the Danforth Center, the stage is set for St. Louis to play a significant role in realizing the real promise of plant genetic engineering, which is to produce genetically-modified plants with desirable traits that directly benefit the consumer. Research reported yesterday at the International Botanical Congress (IBC) gives us a hint of what is to come.
One genetic advance, arguably the most important paper of the IBC, describes Ingo Potrykus's transgenic rice. In developing countries large numbers of people live on simple diets that are poor sources of vitamins and minerals (what botanists called "micronutrients"). Worldwide, the two major micronutrient deficiencies are iron, which affects 1.4 billion women, 24% of the world population, and vitamin A-deficiency, affecting 40 million children, 7% of the world population. The deficiencies are especially severe in developing countries where the major staple food is rice. In research described Tuesday, Swiss bioengineer Ingo Potrykus and his team at the Institute of Plant Sciences, Zurich, have gone a long way towards solving this problem. Supported by the Rockefeller Foundation and with results to be made free to developing countries, the work is a model of what plant genetic engineering can achieve.
To solve the problem of dietary iron deficiency among rice eaters, Potrykus first asked why rice is such a poor source of dietary iron. The problem, and the answer, proved to have three parts:
1. Too little iron. The proteins of rice endosperm have unusually low amounts of iron. To solve this problem, a ferritin gene was transferred into rice from beans. Ferritin is a protein with an extraordinarily high iron content, and so greatly increased the iron content of the rice.
2. Inhibition of iron absorption by the intestine. Rice contains an unusually high concentration of a chemical called phytate, which inhibits iron reabsorption in the intestine -- it stops your body from taking up the iron in the rice. To solve this problem, a gene encoding an enzyme that destroys phytate was transferred into rice from a fungus.
3. Too little sulfur for efficient iron absorption. Sulfur is required for iron uptake, and rice has very little of it. To solve this problem, a gene encoding a particularly sulfur-rich metallothionin protein was transferred into rice from wild rice.