Researchers Reach a Breakthrough for Protein Levels in Key Staple Crop

ST. LOUIS, MO January 27, 2011—  Researchers working at The Donald Danforth Plant Science Center’s International Laboratory for Tropical Agricultural Biotechnology (ITLAB), have made an another advancement in their efforts to improve the root crop cassava which is a major source of calories to 700 million people worldwide, primarily living in the developing world.  A study conducted Dr. Claude Fauquet, Principal Investigator and Director of ITLAB, established a method to provide more dietary protein in cassava.  The results of this research are published in the recent article, "Transgenic biofortification of the starch staple cassava (Manihot esculenta) generates a novel sink for protein," in the PloS One journal

Cassava has many properties that make it an important food source across much of Africa and Asia, it also has many limitations.  For example, cassava has poor nutritional content because it is lacking protein among other micronutrients. 

Although calorie dense, the starchy, tuberous roots of cassava provide the lowest sources of dietary protein among the major staple food crops.  The starchy roots total protein content ranges from 0.7 to 2.5% dry weight compared with 7 to 14% in cereals such as wheat, rice and corn.  Insufficient protein intake often leads to protein energy malnutrition (PEM), which is estimated to affect one in four children in Africa.  Cassava has the lowest protein to energy ratio (P:E) of any staple food, making resource-poor populations that rely on cassava as their major source of calories at high risk of PEM which can lead to permanent physical and mental disabilities and related pathological disorders.

“The ILTAB lab strives to improve cassava productivity and quality through genetic transformation to help less developed countries and we are a step closer to that reality,” said Dr. Claude Fauquet, principal investigator and director of ITLAB at The Donald Danforth Plant Science Center.  “This study will contribute to efforts to end the very real and scary reality that a child dies every six seconds from malnutrition.”

The cassava used in the study was genetically modified to express zeolin, a nutritionally balanced storage protein resulting in total protein levels of 12.5% dry weight within the tissue, a fourfold increase as compared to the non-transgenic controls.  This breakthrough demonstrates that it is possible to increase the PE ratio for cassava to be close that of cereals, and that it is possible to improve essential amino acid composition to directly benefit children.  Initially Fauquet and his team had concern that the modified cassava would have a disrupted physiology and altered phenotype of the transgenic plants.  Greenhouse and field studies revealed this not to be the case, with similar levels of protein accumulation recorded across more than three years of testing in three different locations.

A two-year-old child consuming 50% of his/her dietary energy as wild type cassava would receive about 3 g dietary protein, equivalent to 20% of their daily protein requirement.  The same child consuming the same amount of modified cassava accumulating storage protein at levels achieved in the study would obtain approximately 16 g of dietary protein, or more than 100% of their daily requirement.  This illustrates that genetic modification of cassava has the potential to deliver enhanced nutrition to at-risk populations.

The results prove a concept towards the potential transformation of cassava from a starchy staple, devoid of storage protein, to one capable of supplying inexpensive, plant-based proteins for food, feed and industrial applications.