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and vegetables (such as melons or carrots) make beta-carotene in a series of steps in which precursor molecules are converted to beta-carotene by specific enzymes (which are proteins), one for each step. Rice endosperm lacks three of the required enzymes. To insert beta-carotene, researchers Ingo Potrykus and Peter Beyer and their colleagues in Switzerland and Germany obtained genes for the missing enzymes from daffodils and bacteria. They also isolated genes or regulatory DNA segments from peas, viruses, and other bacteria to help the recombinant enzymes function in rice endosperm. After a decade of effort during the 1990s, the techniques worked. The scientists made rice that contained beta-carotene and identified it immediately by its yellow color (hence: Golden Rice). They published this work in 2000. Figure 13 illustrates the pathway of biosynthesis of beta-carotene and the enzymes replaced by genetic engineering. The pathway illustrates an important distinction: beta-carotene is not the same as vitamin A but is a precursor of the actual vitamin. We (and other mammals) have enzymes that convert beta-carotene to vitamin A in our bodies.19

The technical challenges involved in moving genes from one organism to another—daffodils and bacteria to rice, for example—are daunting, even to experts. Scientists must find the genes for the missing enzymes, reproduce them, and make them function. The “make function” part is particularly challenging. Genes do not work independently. They have to be regulated, which means in this case that the rice needs to be “told” when, where, and for how long the genes for making beta-carotene should do so. Scientists must also find, duplicate, and transfer the genes or DNA segments for these regulatory functions into the rice along with the genes for the missing enzymes. Accomplishing these tasks is a technical tour de force—an art as well as a science—not least because of the extraordinary number of genes and factors required, each requiring its own separate bioengineering step carried out in just the right order. As an illustration of the complexity of this work, table 17 in the appendix (page 302) summarizes the less complicated of the two approaches used to insert beta-carotene genes into rice.

Complicated as they are, the genetic engineering steps are only the first part of realizing the humanitarian benefits of Golden Rice. The inserted genes must be transmitted to seeds; the rice must continue to make beta-carotene when taken out of the laboratory and grown in fields; people must accept, buy, and eat the rice; and the beta-carotene must be absorbed, split into vitamin A, and function in the human body. Table 12 lists these requirements in greater detail. These additional tasks also can be difficult to accomplish. One production problem, for example, is the relative instability of transgenic plants with multiple inserted genes; such plants tend to lose the transgenic traits over several generations. Another is that the scientists engineered beta-carotene into a variety of rice that grows best in temperate zones. To succeed in developing countries, the technology must be transferred to locally grown varieties.

TABLE 12. Research steps required to genetically engineer and to produce and use Golden Rice containing beta-carotene, a precursor of vitamin A

Basic Research (see table 17 in appendix for further details)

Isolate the desired genes and regulatory DNA segments from daffodils, bacteria, peas, and viruses.

Transfer the genes and segments to rice embryos.

Grow the embryos; select the rare embryos that accept the desired genes and segments.

Grow the transgenic embryos into plants.

Harvest seeds from the plants.

Test the seeds for beta-carotene.

Repeat the procedures in rice strains able to grow in tropical climates.

Production Research

Grow the transgenic rice for several generations to ensure the stability of the beta-carotene trait.

Evaluate the plants for environmental effects, presence of allergens, changes in nutrient composition, or unwanted effects on yield.

Obtain regulatory