How to turn cotton into a food crop

The world is currently home to 6.5 billion people and over the next 50 years, this number is set to grow by 50%. With this massive planetary overcrowding, Band Aid’s plea to feed the world seems increasingly unlikely. Current food crops seem unequal to the task, but scientists at Texas University may have developed a solution, a secret ace up our sleeves – cotton.

Cotton is famed for its use in clothes-making and has been grown for this purpose for over seven millennia. We do not think of it as a potential source of food, and for good reason. The seeds of the cotton plant are rife with a potent poison called gossypol that attacks both the heart and liver. Only the multi-chambered stomachs of cattle and other hooved animals can cope with this poison, relegating cottonseed to a role as animal feed.

Getting rid of gossypol could contribute towards reducing the world’s hunger crisis. A fifth of a cottonseed’s weight is made up of oil, and a quarter of high-quality protein, and for every kilogram of fibre, each cotton plant produces 1.65 kg of seed. The plant is a worldwide crop, grown in over 80 countries by some 20 million farmers, the majority of whom live in the poorest parts of the world where starvation is an ever-looming threat. If only the seeds could be made edible.

In 1954, scientists attempted to launched a programme to cross-breed normal cotton plants with a mutant strain that lacked the glands that make gossypol. Unfortunately, they discovered that cotton creates the poison for a reason – it protects the plant’s tissues from insect pests and infections alike. The programme’s seeds were safe for human consumption, but the weakened plants readily succumbed to insect attacks, destroying their commercial potential.

Ganesan Sunilkumar and colleagues at the Institute for Plant Genomics and Biotechnology have solved the problem. They used a technique called RNA interference, or RNAi, to turn off a gene which is essential for gossypol production, called delta-cadinene synthase. But their trick was to put their system under the control of a genetic switch used only in cotton seeds, and not the rest of the plant. As a result, levels of gossypol plummeted in the plant’s seeds and these alone. The rest of its tissues remained as resistant as ever to attackers.

Sunilkumar ran his special plants through a series of tests to make sure that the RNAi’s effects never spread from the seeds to other organs. The plants passed every one and best of all, they stably passed on their characteristics to their daughters. This study is testament to both the power and the precision of modern genetic technology. The researchers identified a very specific point in a biochemical pathway and blocked it in a single part of the plant. The result is a variant that retains the original’s survival abilities, but is suddenly fit for human consumption.

Their approach has tremendous potential for opening up other food sources. For example, the beans of the tropical grass pea, Lathyrus sativus, are often eating by poor people in Africa and Asia in times of dire need. As the beans contain a potent neurotoxin – a nerve poison – those eating them often contract a neurological disease called lathyrism. With Sunilkumar’s technique, lathyrism could become a thing of the past.

For those who feel that the use of such technology is tantamount to playing God, consider this. Every year, 44 million tons of cottonseed are wasted. With this new technology, the engineered seed could provide enough protein for half a billion people every year.

Reference: G. Sunilkumar, L. M. Campbell, L. Puckhaber, R. D. Stipanovic, K. S. Rathore (2006). From the Cover: Engineering cottonseed for use in human nutrition by tissue-specific reduction of toxic gossypol Proceedings of the National Academy of Sciences, 103 (48), 18054-18059 DOI: 10.1073/pnas.0605389103