Where's the Super Food?

Scientists have genetically engineered several biofortified food plants to tackle a scourge of developing countries—micronutrient malnutrition. The crops have yet to be planted on a wide scale, but that may be about to change.

© Lynn Johnson / National Geographic Image Collection

ight now, one billion people are starving. That’s one in every six people on this planet. The number of these hungry people is roughly equivalent to the populations of the United States, Indonesia, Brazil, Pakistan, and Bangladesh combined.

The world reached this bleak milestone in the middle of June this year. With the global human population continuing to explode and resources being stripped at an increasing rate, the outlook is not good. More people will go hungry. Less will have access to the nutrients their bodies need. And more will succumb to the illnesses that take advantage of the malnourished body. More people will...

But this is only half the story. The insidious corollary to the global hunger crisis is that even more people—at least half the world’s population, according to a 2004 United Nations report—suffer from micronutrient malnutrition. People suffering from this “hidden hunger” may consume sufficient calories, but lack suitable amounts of essential nutrients, vitamins, and minerals. These legions of nutrient-starved people largely reside in developing countries. Their plight is dire. Even mild micronutrient deficiencies can increase infant mortality rates and lead to cognitive impairment and immune system problems in children, among other serious health issues.

In addressing global hunger and micronutrient malnourishment, biotechnology holds potential solutions: specifically, nutritionally enhanced, transgenic crops. The technology that makes these plants possible took center stage in January 2000 with the publication of a brief but high-impact Science paper on the creation of a prototype that would become known as “Golden Rice,” packed with beta-carotene (also called pro-vitamin A), the precursor to vitamin A and an essential component of healthy diets.1 Genetically modified (GM) crop plants were already becoming commonplace, but existing genetic changes mostly endowed plants with desirable producer traits, such as herbicide or pest resistance in soybeans or cotton plants. To create Golden Rice, European scientists, with funding from the Rockefeller Foundation, inserted bacterial transgenes into the latent pro-vitamin A biosynthesis molecular pathways in wild-type rice, which contains no pro-vitamin A. This modification transformed the normally nutrient-poor endosperm—or kernel—of milled rice into a source of beta-carotene.

Their work was trumpeted on the cover of TIME magazine with the headline: “This rice could save a million kids a year,” preventing night blindness and other disorders caused by low vitamin A, a nutrient often lacking in developing world diets. While it got people talking and thinking about the potential of genetic engineering to salve the world’s hunger pangs, Golden Rice also set up a contentious debate that still rages today. “[Golden Rice] was something that attracted the attention of both opponents and proponents in the same way,” recalls Peter Beyer, a plant biochemist at the University of Freiburg in Germany and one of Golden Rice’s inventors.

Nutritionists took Beyer and his co-inventor, now-retired biologist Ingo Potrykus, to task, pointing out that Golden Rice could do little to address vitamin A deficiencies in the developing world because its beta-carotene content was too low. Beyer says that anti-GM groups “hijacked” the issue and used Golden Rice as a springboard to rail against all GM crops. Largely due to this controversy, along with political and technological obstacles, nearly 10 years after it was unveiled, Golden Rice has yet to make its wide debut in the paddies of the developing (and vitamin A–deficient) world. “Once [the science] is there, your initial belief is that your work is done, but by far it is not,” says Beyer.

But Beyer, Potrykus, and several collaborators have continued to forge on, refining the technology that made Golden Rice possible and amassing a larger consortium to try to get the enhanced staple crop into the dinner bowls of the people who most need it. And the failure of Golden Rice to leap directly into the world’s rice paddies has not dissuaded scientists from trying the same with other enhanced crops: carrots with twice the calcium, tomatoes with 20% more antioxidants, cassava boosted with additional iron, protein, and vitamins. There are dozens of reports in the scientific literature of common food plants that have been engineered to produce increased levels of one nutrient or another. One cannot yet find vast paddies of Golden Rice waving in the tropical sun or fields of super-cassava blanketing African farmland, but this may be about to change.

More than 250 million sub-Saharan Africans rely on the cassava, a starchy tuber native to South and Central America, as their staple food. Cassava supplies 38.6% of the caloric requirements in some parts of Africa, where hunger and nutrient deficiencies grip the populace and more than 40% of global cassava production takes place.

But cassava is not a particularly nutrient-rich food. It lacks much of the iron, zinc, and vitamins A and E that healthy bodies need to grow. University of Nebraska–Lincoln biochemist Ed Cahoon has worked for several years as part of the BioCassava Plus program, which aims to improve the nutritional profile of cassava through genetic engineering.

Launched in July 2005 with $7.5 million from the Bill and Melinda Gates Foundation’s Grand Challenges in Global Health Initiative, the program’s overarching goal is to develop what essentially amounts to a super-charged cassava plant variety—one with increased levels of iron, zinc, protein, vitamins, and resistance to the cassava mosaic and brown streak viruses plaguing African farmers.

The program has started by developing separate GM cassavas with each of these nutritional improvements one by one. Cahoon and his colleagues have produced a beta-carotene–enhanced cassava by inserting genes that impart higher levels of the pro-vitamin (and give an orangey glow to the normally pallid root). They inserted a gene called phytoene synthase (psy) originally derived from the soil bacterium Erwinia herbicola (and also used to develop Golden Rice), which codes for an enzyme that catalyzes a crucial step in the beta-carotene biosynthetic pathway.

The researchers packaged psy into the plasmid of a disarmed Agrobacterium—the workhorse of plant genetic engineering—together with a root-specific promoter derived from potatoes, a 5´ leader sequence consisting of plant DNA that shuttles the protein into root-bound plastids, and the standard 3´ untranslated region (UTR) from mRNA. Cahoon recalls the first time he saw the successfully engineered cassava root (the part of the plant that’s eaten), in 2007. “It was a good day,” Cahoon says. “[The cassava] was noticeably orange.”

Cassava ß-Carotene is a dietary precursor of vitamin A that is synthesized by the methylerythritol phosphate (MEP) pathway in plastids of some plant cells. Conventional cassava roots lack some of the essential enzymes necessary to produce ß-carotene. The initial step in the pathway is controlled by deoxyxylulose-5-phosphate synthase (DXS), which is added to Cahoon’s cassava via the gene dxs , originally sourced from a different plant species. Additional steps generate the C5 isopentenyl diphosphate (IPP) that is used as the building block for the synthesis of the C20 geranylgeranyl diphosphate (GGDP). Phytoene synthase (PSY), the product of an introduced gene (psy) from a bacterial source, combines two molecules of GGDP to form phytoene, which is converted to ß-carotene via lycopene through a series of desaturation, isomerization, and cyclization reactions. The end result is a noticeably more orangey cassava root.

Meanwhile, Cahoon decided to try inserting the Arabidopsis gene, 1-deoxy-d-xylulose 5-phosphate synthase (dxs), which regulates the isoprenoid pathway, a set of biochemical reactions further upstream from the biosynthetic step in which psy is involved. Inserting dxs, which increases the amount of chemical precursors to beta-carotene, was “like turning up the whole isoprenoid pathway,” Cahoon says. He found that inserting both the psy and dxs genes resulted in a cassava even more orange than the roots with only the psy modification—and with 30 times more beta-carotene than normal roots.

“It’s an informal chain of influence that discourages African farmers from planting any GM crops at all.”

After running more greenhouse trials on plants with both the single and double genetic modifications and choosing the cassava with the most beta-carotene, Cahoon and his team sent tissue samples to Puerto Rico, where scientists propagated clonal offspring. Now, the cassava plants are growing in field trials, which Cahoon recently visited. “They’re looking good,” he says. “For the most part they look like the control plants,” which contain normal levels of beta-carotene.

Eventually, the BioCassava Plus program hopes to move into its second phase—set to commence in 2010 with an additional infusion of funding—in which nutritional modifications to increase iron, zinc, protein, vitamins, and virus resistance will be combined into one cassava plant. “We would actually address all of the deficiencies in cassava in a single cultivar,” says Richard Sayre, a molecular biologist at the Danforth Plant Science Center in St. Louis and director of the BioCassava Plus program. But, as he and Cahoon learned from Golden Rice, getting the science right is just the first step.

Ed Cahoon examines cassava plants at field trials in Puerto Rico in May
Photo By Nigel Taylor, PHD

There are reasons Cahoon and his colleagues picked Puerto Rico as the site of field tests for the beta-carotene–boosted cassava. Puerto Rico enjoys a tropical climate like much of the core cassava growing areas of Africa but, equally important, the island territory operates under the laws and regulations of the United States, not Africa. “It’s not Africa, but getting in the field in Puerto Rico is a much simpler process than getting through the regulatory processes in Africa,” Cahoon says.

It’s this regulatory tangle facing GM crops in much of the world, including Africa, that largely explains why many transgenic plants that could address widespread nutrient deficiencies are trapped in laboratories instead of growing in soil.

According to Val Giddings, president of Prometheus Agricultural Biotech, most of the restrictions stem from European politics, as influenced by vocal anti-GM groups. Giddings, who helped craft the US Department of Agriculture’s GM crop regulations in the early 1990s as a geneticist at the agency’s Animal and Plant Health Inspection Service (APHIS), says that European countries have effectively exported their restrictive regulations by “making their overseas development programs a slave to their domestic political policies.” In 2004, American officials entreated EU officials to reassure three African nations—Zimbabwe, Zambia and Mozambique—that the hundreds of thousands of tons of GM food aid they had rejected was in fact safe; the EU refused. Add to this the influence that European importers and governments have over food producers in Asia and Africa, and the developing world’s soil is rendered pretty infertile for GM crops. Robert Paarlberg, a Harvard political scientist and author of the book Starved for Science, concurs about the difficulties in getting biotech crops into developing nations. “It’s an informal chain of influence,” he says, “that discourages African farmers from planting any GM crops at all.”

Even in the United States, GM regulations are cumbersome and require a team of people to navigate. Agricultural biotech entrepreneurs, like drug developers, often cite a 10-year time frame to go from initial discovery to saleable product. But compared to the European system, the US regulatory system is manageable. For the beta-carotene–fortified cassava to gain approval from the Department of Agriculture (USDA), for instance, the agency would require data indicating that the introduced genetic construct stably integrated, that the introduced gene does not cause plant disease or produce an infectious agent, and that the cassava was not modified using a gene derived from human or animal pathogens, among other criteria. “It may feel cumbersome to people, but I don’t think [the regulations] are unreasonable,” says Mark Manary, a pediatrician at Washington University in St. Louis who collaborates on the BioCassava Plus program and spends more than half the year working with aid groups in the African nation of Malawi.

However, even if scientists get past the regulatory hurdles associated with any GM foods, there is another practical obstacle that stands in the way of fields full of nutrient-packed cassava or carrots: These foods will cost more than the non-modified versions, and the people who most need them are also the least able to afford them.

In a basement lab at a DuPont research facility, a technician loads bright green soybean tissue samples into a “gene gun,” an unassuming contraption that looks more like a toaster oven than a firearm, and shoots gold nanoparticles coated with DNA molecules into soybean cells at more than 1500 kilometers per hour. The machine makes a muffled pop and the deed is done. DNA will incorporate into the soybean genome and inhibit the activity of fatty acid saturase-2, an enzyme that normally catalyzes the biochemical conversion of oleic to linoleic acid in the soybean plant. Plant molecular biologist Ted Klein stands by, watching. “If we knock out the expression of that enzyme, specifically, in the seed at the right time, then there’s no detrimental impact on the whole plant,” he says.

Cathie Martin's purple tomatoes have 20% more anthocyanins than conventional ones.
Photo by Andrew Davis and Sue Bunnewell

Elsewhere in DuPont’s Wilmington, Del.–based experimental station, giant walk-in coolers feature lines of bright fluorescent bulbs glowing above rows of the modified soybean plants that grew from tissues earlier shot with the gene gun. While they may not address nutrient deficiencies in poverty-stricken corners of the globe, these plants may one day reduce the need to use hydrogenated oils—AKA the dreaded trans fats—in frying, for example. For now, the plants simply stretch to gather as much of the light as possible; eventually, they will produce oil that is more stable in storage and cooking conditions, with 20% less saturated fat and a higher proportion of oleic acid than normal soy oil. The company will screen these soybeans in the grow room looking for the best phenotypes, which develop after several semi-random gene gunshots. DuPont and Pioneer Hi-Bred, the DuPont company that managed the research and development of the technology behind the plants, known as Plenish, hopes to sell “high oleic oil” from the beans to food processing companies, restaurant chains, and other industrial customers around the world as early as the end of this year. With such a market, the company isn’t too concerned about finding customers who can afford the technology.

Tomato Anthocyanins are types of antioxidants, which have been linked to many health benefits. Adding two genes (Del and Ros1) originating from the snapdragon genome to conventional tomatoes, leads to the upregulation of several key enzymes in the pathway, including phenylalanine ammonia lyase (PAL), anthocyanidin synthase (ANS), flavonoid 3-O-glucosyltransferase (3-GT), flavonoid 3-O-glucoside-rhamnosyltransferase (RT), anthocyanin acyltransferase (AAC), flavonoid-5-glucosyltransferase (5-GT), and glutathione S-transferase (GST) and putative anthocyanin transporter (PAT), which may be involved in transport of anthocyanins into the vacuoles of cells within the tomato's flesh. The end result is a tomato with a threefold increase in antioxidants and very empurpled flesh.

The oil has already been approved by Mexican and Canadian regulatory agencies. “Now we’re just waiting for the USDA,” says Susan Knowlton, a DuPont research manager.

Other scientists are also trying to tweak the nutritional content of common foods. Kendal Hirschi, a Baylor University pediatrician and geneticist, has genetically engineered a carrot that contains twice the calcium of normal carrots by upping the expression of a plant calcium transporter (sCAX1) in the roots with the addition of an Arabidopsis gene construct. He’s even performed a pilot nutritional study, which was funded by the National Institutes of Health, where subjects absorbed about 40% more calcium from his carrots than they did from normal carrots.2 Feeding studies are essential if nutritionally enhanced GM foods are going to have a real-world impact, Hirschi says. “None of these improvements are any good until we actually show they’re good in the food supply.”

In order to ensure that the technology has a buyer, that could perhaps compensate for the expense of distributing it free or below cost to the developing world, Hirschi is trying to attract attention from large food company General Mills, which has expressed some interest in his carrots as a way to make thicker canned soups. (Calcium chloride is often added to foods as a thickener.)

Cathie Martin, a geneticist at the John Innes Centre in Norwich, UK, has developed a tomato variety that may prove useful to consumers worldwide, not just the malnourished. Martin’s deep purple tomato has 20% higher levels of anthocyanins, antioxidants that may guard the body against chronic diseases and cancer. She and colleagues recently showed that mice consuming a diet that includes her GM tomatoes, whose boosted antioxidant profile is thanks to two transcription factors from snapdragons, lived an average of 30% longer than mice that consumed regular tomatoes.3 Western countries—where people tend not to get the recommended 5 fruits and vegetables per day, and the giant food companies that operate therein—can play a role in moving these types of GM foods closer to a widespread reality, Martin says. “You’ve got to get the food companies interested in sowing better foods,” she says. “If you can improve tomatoes, then you can get the good things in fruit and vegetables into something that people actually eat.”

“We know how this story ends,” says Val Giddings—nutritionally fortified, GM foods will get into the global marketplace and the mouths of the people who need them. “You can’t stop the tide. Biotech will, in time, become the new conventional agriculture. The question is how long will it be until that happens, and what, if anything, can we do to accelerate the process.”

There are hints now emerging that bear out Giddings’ prediction. Since first introducing the world to Golden Rice in 2000, Beyer’s collaborators have developed new versions of the beta-carotene–enhanced grain. Golden Rice 2, which Beyer says will be available on the market in the Philippines and in Bangladesh within the next 2 or 3 years, contains 30–35 micrograms of beta-carotene/gram—more than 30 times more beta-carotene than the original kernel introduced in 2000.4 Beyer and his colleagues accomplished this massive increase by tinkering with the promoter sequences used in the genetic modification, by changing the source of one of the gene inserts from daffodils to maize (which boosts beta-carotene production), and other subtle tweaks to the science behind Golden Rice. This new version recently completed feeding trials5 and is now growing in experimental plots in the Philippines and Bangladesh.

Golden Rice Wild-type white rice produces geranylgeranyl-diphosphate (GGPP), a precursor of ß-carotene. However, the grain endosperm lacks phytoene synthase, which catalyzes the conversion of GGPP to phytoene. Golden Rice 1 was engineered to express daffodil phytoene synthase, while Golden Rice 2 uses a more efficient maize version of the gene. Zeta-carotene desaturase, an enzyme expressed by a gene from the soil bacterium Erwinia uredovora, further increases ß-carotene levels in the grain.

But the research was relatively easy—to create a GM product that regulators and citizens would accept, Beyer needed help. Funding came from philanthropic organizations, such as the Bill and Melinda Gates Foundation, the Rockefeller Foundation, and government aid agencies, such as the United States Agency for International Development. A private-public partnership between Golden Rice’s inventors and the agrichemicals company Syngenta, along with several collaborations with research institutions throughout Asia, made the imminent market introduction of Golden Rice possible, Beyer says. The project is now conducting the social marketing research and local rice variety back-crosses, which will blend the beta-carotene trait into locally popular rice varieties—both necessary to successfully and safely introduce the crop and get farmers to grow the plants.

The BioCassava Plus program has also recently seen significant progress in its goal to introduce biofortified foods into the developing world. Director Richard Sayre says that the program’s pro-vitamin A cassava plants have been approved for field trials in Nigeria, the world’s number one consumer of the food. In July, the country planted between 4000 and 8000 m2 with Cahoon’s two-gene GM cassava, the first GM product Nigeria has field tested. “We are quite proud of that,” Sayre says. To advance the BioCassava Plus program to the next stage, Sayre says that more donor money will be needed. He says that the program is “planning on approaching other donors,” but declined to name them.

Navigating through Nigeria’s regulatory approval process was no small task, Sayre says, for which the BioCassava Plus program enlisted the help of Nigeria’s National Root Crop Research Institute (NRCRI) and a Nigerian product developer who was a former member of the county’s National Biosafety Committee. “We think that was an important part of our strategy,” Sayre says, “because it meant that the government was buying into the process.” The Nigerian regulations, for example, required experimenters to dig a fence around the experimental plots a meter deep into the soil to prevent burrowing animals from carrying off bits of the GM cassava. The Nigerian regulations were “redundancies upon redundancies of protection,” according to Sayre.

“You can’t stop the tide. Biotech will, in time, become the new conventional agriculture.”

To ensure the cassava gets where it needs to go, the project will again call upon the infrastructure and local knowledge of national agriculture research institutions such as the NRCRI and nongovernmental organizations to distribute the cassava plants to poor farmers for free or for a nominal fee. The BioCassava Plus project will utilize the traditional dissemination scheme—where farmers share cuttings of their successful plants with friends and neighbors—to further disseminate their enhanced cassava. (The Gates Foundation, in fact, requires that the technology come with royalty-free humanitarian license.) Poor farmers can get and share cuttings for free, while those who make more than $10,000 per year must pay a royalty fee to companies like Monsanto that donated enabling technologies (patented Agrobacterium transformation systems, and gene promotors, for example) to the project. Sayre also says that a “very critical” part of the BioCassava project is to eventually transfer research and production capabilities and responsibilities to African labs, scientists, and countries. “I put myself out of business in many ways,” he says.

Golden Rice 2 contains more than 30 times more beta-carotene than the first Golden Rice.
Photo courtesy of Golden Rice Humanitarian Board

Other GM advocates say they hope cassava is not the only biofortified food to be planted in Nigeria. “What I’d like to see is hundreds of millions of very poor people improving their nutritional status and improving their health status,” says Lawrence Kent, senior program officer of agricultural development at the Bill and Melinda Gates Foundation, which funds genetic research in biofortification, but also donates money to efforts aimed at conventional fortification, supplementation, and dietary diversification. “We’re hoping some initial successes are going to trigger additional interest, especially from national governments. If we can help get more nutrients into these staple foods, we really can help millions of people improve their lives.

The original version of "Where's the Super Food?" included a photo caption stating that Golden Rice 2 has more than 30% more beta-carotene than the first Golden Rice. It should have read that Golden Rice 2 has more than 30 times more beta-carotene than the first Golden Rice. Also, the article gives the title of Robert Paarlberg's book as Starving for Science, when it is in fact Starved for Science. The Scientist regrets these errors.

1. X. Ye et al., “Engineering the provitamin A (beta-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm,” Science, 287:303–5, 2000.
2. J. Morris et al., “Nutritional impact of elevated calcium transport activity in carrots,” PNAS, 105:1431–35, 2008.
3. E. Butelli et al., “Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors,” Nat Biotech, 26:1301–8, 2008.
4. J.A. Paine et al., “Improving the nutritional value of Golden Rice through increased pro-vitamin A content,” Nat Biotech, 23:482–87, 2005.
5. G. Tang et al., “Golden Rice is an effective source of vitamin A,” Am J Clin Nutr, 89:1776–83, 2009.

Interested in reading more?

Magaizne Cover

Become a Member of

Receive full access to digital editions of The Scientist, as well as TS Digest, feature stories, more than 35 years of archives, and much more!
Already a member?