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Feeding Future Populations with Nutritionally Complete Crops

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Sonia Gomey-Galera, et al., ISB News Report, January, 2010

It sounds too much to hope for when we look around the real world and see that up to half the population lacks access to a balanced diet. The best way to provide adequate supplies of essential vitamins and minerals is to eat a varied diet, including fresh fruit and vegetables, fish, and dairy products. In the West, an adequate diet can be achieved by visiting the supermarket or grocery store, but in developing countries many people subsist on monotonous diets of staple cereals, such as rice, corn, and wheat. Although they provide calories, cereal grains are poor sources of most vitamins and minerals; a diet comprised mostly from cereals will address hunger, but not malnutrition. Micronutrient deficiency diseases are therefore rife in the developing world, causing millions of needless deaths and adding to miserable socio-economic conditions.

Many strategies have been proposed to address nutrient deficiencies, including supplement distribution, fortification programs, and attempts to make crops more inherently nutritious.4 Unfortunately, such programs have had limited success: first, because they require significant funds and a good organizational infrastructure, both of which tend to be lacking in developing countries; and second, because they rely on compliance from farmers and consumers. Fortification programs have been successful in some cases, e.g., salt iodization, but these are rare exceptions and merely shift the problem onto the remaining nutrient deficiencies. Biofortification is the most ambitious approach, as it attempts to address the problem at the source. For example, the levels of several mineral nutrients in crops can be improved by including mineral salts in fertilizers. As above, however, there has only been limited success, and only when there is a good infrastructure and enough money to pay for fertilizers. This excludes a significant proportion of the most malnourished people in the world, who cannot afford the technical measures to improve the nutrient content of their own crops.

A relatively new approach is to create novel crop varieties that are more nutritious, thereby removing the onus of compliance from producers and consumers alike. There is significant genetic variation in the quantity of some nutrients, so breeding crops and selecting those with higher levels of vitamins and minerals seems like a logical approach.1 Unfortunately, trying to enhance nutrient levels by conventional breeding is a very long-term venture, particularly when the aim is to transfer nutrient-rich traits into locally-adapted breeding varieties. Even if this could be achieved in a reasonable time scale, the complexity of breeding for several different nutrients at once would be insurmountable, and some nutrients are simply not present at high enough levels to make breeding a viable option. Conventional breeding is therefore a dead end when constructing a visionary strategy for generating nutritionally complete cereal crops.

What can be done? An important principle of nutrition is that minerals and vitamins are very different beasts. Minerals are inorganic compounds. They cannot be synthesized from other molecules and must be obtained from the environment. To make plants rich sources of minerals, those plants must be persuaded to remove minerals from the soil and stockpile them.5 In contrast, vitamins are organic molecules that can be synthesized from basic organic compounds like sugars and amino acids, given appropriate enzymes. To make plants rich sources of vitamins, those plants must be endowed with the ability to synthesize them.4 The key is to take the part of the plant that is eaten (for cereals this would be endosperm of the seed) and modify it to increase its ability to store minerals and capacity to synthesize vitamins.

The idea of metabolically engineering plants to produce high levels of vitamins is not new. Many research papers have been published that describe plants with sometimes astonishing levels of key nutrients, and there have been several widely publicized successes such as Golden Rice, containing such high levels of the vitamin A precursor ß-carotene that rice grains appear golden yellow in color.

 Although these successes have advanced the field significantly and provided hope that individual deficiency diseases can be eliminated or reduced, the enhancement of single nutrients still leaves a massive gap in the nutritional welfare of populations targeted with such crops. To avoid the disappointing yet inevitable outcome of such strategies, which could be to solve one deficiency problem only for another to arise in its absence, the focus for metabolic engineering strategies of the future should be to provide nutritionally complete crops.