*This page was produced by Ashley Cain as part of an assignment for an undergraduate course at Davidson College*
After working with genetically modified organisms for over twenty years, Ingo Potrykus of the Swiss Federal Institute of Technology began focusing his research on golden rice. In the 1970s and 80s Potrykus worked with a variety of plants, beginning with an attempt to transfer genes into the Petunia. With the help of fellow researcher Swappan Datta, Potrykus was able to make the first transgenic rice in the late 1980s. Datta and Potrykus developed hygromycin resistant Indica Rice and later insect-resistant rice. While working on these developments, Potrykus realized the need for increased nutrient levels in the foods of developing countries. Potrykus then began investigating the possibility of transgenic rice that could produce the nutrients needed by the malnourished people in developing countries (Potrykus, 2001).
In 1992 Potrykus met with Peter Beyer, an expert on the biochemistry of the daffodil. Process at a Rockefeller foundation sponsored brainstorming session.(Nash, 2000). Following their meeting, these researchers began the project of creating Golden Rice. They received $100,000 from the Rockefeller foundation and were also supported by the Swiss government and the European Union. All total the researchers spent seven years and $2.6 million on the development of Golden Rice (Nash, 2000).
In the initial meeting between the scientists the possibility of accomplishing the golden rice goal seemed unlikely. To begin their work Peter Burkhardt, a graduate student working with Potrykus, began the process of gaining information on “isoprenoid biosynthesis in rice endosperm” (Burkhardt et al., 1997). Using radioactively labeled carbon the investigators determined that no carotenoids were produced in rice endosperm. They then discovered the presence of geranly geranly disphosphate (GGPP), “the substrate specific for the first carotenoid-specific biosynthetic reaction” (Burkhardt et al., 1997). In order to synthesize beta-carotene from GGPP four enzymes would be needed. These enzymes included phytoene synthase which catalyzes the conversion of GGPP to phytoene. Next, phytoene desaturase converts phytoene to gamma carotene. Then gamma carotene desaturase catalyzes the formation of lycopene from gamma carotene. Finally, lycopene cyclase catalyzes the formation of beta carotene from lycopene. cDNA coding for each of these specific enzymes must be inserted into the rice endosperm in order to complete the biosynthetic pathway (Burkhardt et al., 1997). Potrykus claims that “There were hundreds of scientific reasons why the introduction and coordinated function of these enzymes would not be expected to work and that it may cause problematic side effects” (Potrykus, 2001). Although the challenge seemed impossible to anyone with a scientific background, the overall goal of saving children's lives and preventing blindness was too important (Potrykus, 2001).
In 1997 Peter Burkhardt, working at the Swiss Federal Institute of Technology developed the first major breakthrough in the quest for golden rice. Using cDNA that encoded for the daffodil psy gene, a nuclear gene encoding phytoene synthase, Burkhardt transformed the rice endosperm. This transformation was conducted using microprojectile bombardment (see genetic modification techniques) (Burkhardt et al., 1997). From this transformation Burkhardt obtained phenotypically normal rice endosperm which produced phytoene synthase. This development demonstrated the ability to alter the biosynthetic pathways of rice endosperm with no physiological or developmental consequences (Potrykus, 2001).
Following this breakthrough Potrykus and his lab continued working toward their goal. The researchers' hope was to create transgenic plants for each enzyme and then cross them to create a plant with cDNA coding for all four enzymes. Their attempts to create a transgenic plant producing phytoene desaturase lead to phenotypically irregular plants (Potrykus, 2001). Following the work of Burkhardt and other scientists, Xudong Ye began working on the golden rice project. In contrast to previous experiments ye utilized agrobacterium (see genetic modification techniques) in order to transfer cDNA into the rice endosperm. Ye also chose to introduce the cDNA of all four genes in a single transformation effort (Ye et al., 2000). From this transformation event Ye produced ten fertile and phenotypically normal plants, each producing all four genes. The endosperm of these plants' seeds were isolated and appeared yellow, indicating carotenoid production (Ye et al., 2000). Ye and his group had developed golden rice. Many of his plants showed up to 85% carotenoid synthesis being beta-carotene. The plants also showed an increase in lutein and zeaxanthin production, two additional nutritious substances (Potrykus, 2001).