November 21, 2006

RNA interference used to make cotton seed edible

From the New Scientist, cotton that has been genetically engineered so its seed is no longer toxic could provide protein-rich food for poor countries. The researchers say the technology used could make other toxic plants safe to eat.

Cottonseed contains about 22% protein, and the cotton already produced worldwide has enough protein to meet the requirements of 500 million people. But it also contains the toxin gossypol, making it poisonous to animals, including humans.

Rathore and his colleagues achieved this – after what he says has been a 10-year race with teams in China and Australia – using RNA interference (RNAi) technology.

The team chose to target an enzyme that is critical in the production of gossypol. They constructed a genetic sequence that would only be active in cotton seeds and which contained a portion of the enzyme’s gene, followed by the same sequence in reverse. They introduced their construct into cottonseed cells. There, it generated a strand of messenger RNA with two halves which stuck to each-other in a hair-pin shape.

In cells, this hairpin RNA gets chopped up into small bits by a "dicer enzyme" and, through a mechanism that is not completely understood, the small bits stick to the original enzyme’s messenger RNA. This tags the RNA, labelling it for destruction by a cellular mechanism known as the RISC complex. The net result is that the production of gossypol in the modified cottonseeds is interrupted.

Other crops can be amde safe to eat, such as Lathyrus sativus, also knows as grass pea, chickling vetch, or Indian pea. This legume is an emergency crop which farmers in Asia and Africa plant in times of drought because it is resists the toughest growing conditions.

It will be ten years of safety checks and other processes before the cottonseed is on sale.