Crop Biotech Update

Transgenic Yellow Cassava to Address Vitamin A Deficiency

October 8, 2010

The roots of cassava (Manihot esculenta) serve as a primary carbohydrate source in the diets of people in the arid tropics. However, commercial cassava cultivars have limited amount of micronutrients in their roots, and micronutrient deficiencies, especially deficiency in vitamin A, are rampant in the arid tropic regions. Thus, Professor Peter Beyer of University of Freiburg, Germany, studied a naturally arising yellow-rooted cassava to investigate the synthesis of beta-carotene, which transforms into vitamin A when consumed. The yellow-rooted variety was compared with cultivars with white, cream, and yellow roots and they found out that the yellowish roots have more carotenoids. They traced the cause of higher carotenoid levels and found the answer in the single amino acid of phytoene synthase (PSY), an enzyme that works in the biochemical pathway that produces carotenoids. PSY genes improve the entry of carbon in the pathway, leading to the production of more beta-carotene in the roots. They were also able to turn a white-rooted cassava into a transgenic yellow-rooted cassava by overexpressing the PSY genes. The resulting transgenic cultivar contains more beta-carotene.

Read the abstract of this study at