Washington, July 1 : An international team of scientists has engineered how to fortify the cassava plant - a staple root crop - with enough vitamins, minerals and protein so that it can provide a day's worth of nutrition in a single meal.
The team has further engineered the cassava plant so that it can resist the crop's most damaging viral threats and are refining methods to reduce cyanogens, substances that yield poisonous cyanide if they are not properly removed from the food before consumption.
The reduction of cyanogens also can shorten the time it takes to process the plant into food, which typically requires three to six days to complete.
The international team, led by Richard Sayre, a professor of plant cellular and molecular biology at Ohio State University, hopes to translate the greenhouse research into a product that can be field tested in at least two African nations by 2010.
Sayre presented an update on the BioCassava Plus project June 30 at the American Society of Plant Biologists meeting in Merida, Mexico.
"This is the most ambitious plant genetic engineering project ever attempted," Sayre said.
"Some biofortification strategies have the objective of providing only a third of the daily adult nutrition requirements since consumers typically get the rest of their nutritional requirements from other foods in their diet. But global food prices have recently gone sky high, meaning that many of the poorest people are now eating just one meal a day, primarily their staple food," Sayre added. The roots of cassava can be banked in the ground for up to three years, providing food security, but the plant must undergo time-consuming processing immediately after harvest to remove compounds that generate cyanide. Unprocessed roots also deteriorate within 48 hours after harvest, limiting the food's shelf life.
Sayre and colleagues from multiple institutions set out to tackle virtually all of cassava's problems to make the plant more nutritious and to increase the crop's revenue-producing potential for farmers.
The labs in the project have used a variety of techniques to improve on the model cassava plant used for the research. They used genes that facilitate mineral transport to produce a cassava root that accumulates more iron and zinc from the soil.
To fortify the plants with a form of vitamin E and beta-carotene (also called pro-vitamin A because it converts to vitamin A in the body), the scientists introduced genes into the plant that increase terpenoid and carotenoid production, the precursors for pro-vitamin A and vitamin E. They achieved a 30-fold increase in pro-vitamin A, which is critical for human vision, bone and skin health, metabolism and immune function.
Adding protein to the cassava plant has posed a challenge, Sayre said. The scientists discovered that most of the nitrogen required to make the amino acids used for protein synthesis in roots is derived from the cyanogens that also cause cyanide toxicity.
So their strategy for increasing protein levels in roots focuses on accelerating the conversion of cyanide-containing compounds into protein rather than completely eliminating cyanogen production, which would hinder the efforts to increase protein production, Sayre explained.
To further address the cyanide problem, the scientists have also developed a way to accelerate the processing methods required to remove cyanide - a days-long combination of peeling, soaking and drying the roots before they are eaten.
To strengthen the cassava plant's resistance to viruses, the scientists introduced a protein and small interfering RNA molecules that interfere with the viruses' ability to reproduce.