27 May 2009

Genetically engineering a complete meal

Scientists have genetically modified white corn to increase the levels of three different vitamins — bringing closer crops that can deliver full nutritional requirements.
Vitamin rich corn

Deep orange elite inbred South African corn accumulating high levels of beta carotene (pro vitamin A) in addition to vitamin C and folic acid (vitamin B9). Credit: PNAS

LONDON: Scientists have for the first time genetically modified white corn to increase the levels of several different vitamins — bringing closer the prospect of crops that can deliver full nutritional requirements.

The team increased the levels of beta-carotene, the precursor of vitamin A, 170-fold; levels of vitamin C six-fold; and also doubled the folic acid in the African staple.

White corn normally contains only trace amounts of beta-carotene. Diseases caused by low consumption of vitamin A, vitamin C and folate are widespread in Africa, says lead researcher Paul Christou of the University of Lleida in Spain.

Bombarded with genes

Until recently researchers had struggled to introduce multiple genes into a plant simultaneously to create several different traits, he said.

His team developed a method that transfers the desired genes into plant embryos by bombarding them with gene-coated metal particles. The resulting plants are then screened for those containing the required genes.

The method can introduce an unlimited number of transgenes into any plant, says Christou. The method is quicker than others and the genes persist in subsequent generations.

Most researchers do it “the hard way” by putting individual genes into plants and then crossing and breeding them sexually. Those containing two different traits are crossed again and so on. “It would take years … we can do it in one shot,” he says.

The team is now trying to introduce genes for other vitamins into the corn along with microelements such as calcium, iron, selenium, and zinc, and genes for resistance to insects and the parasitic plant striga. The researchers are also introducing genes into varieties of rice.

Tri-vitamin crop

They aim to have prototype plants containing 25 to 30 transgenes in five years, but getting them past GM regulatory processes and into the field will be the difficult part, say Christou.

After field trials in the United States next year, the team will use conventional breeding to cross the tri-vitamin crops with local varieties.

The research shows the value of biotechnology for simultaneously improving multiple nutritional traits, says Ed Cahoon of the U.S.-based University of Nebraska and part of the BioCassava Plus project, an initiative to engineer cassava into a complete meal.

The project has so far introduced genes for increased nutrient content, virus resistance and decreased cyanide content individually into cassava and field trials will be carried out in Nigeria.

He says the method of “stacking” genes has been used commercially before — to confer resistance to herbicides and insects in maize, for example — and that this research extends the technology to have direct value to consumers.

The research was published last month in the Proceedings of the National Academy of Sciences.

More information:
The study in PNAS

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