Engineering Cassava for High Beta Carotene and Understanding the Impact of Other Metabolic Genes in Carotenoid Pathway

Hundreds of millions of people in tropical climates depend on cassava as a major source of caloric intake. However, a diet based mainly in cassava does not supply the necessary intake of essential nutrients and vitamins, resulting in chronic and widespread malnutrition. As published by the World Health Organization, 250 million children suffer from vitamin A deficiency, and this malnutrition leads to blindness, infection, disability and death in about 250,000 to 500,000 children yearly. These “orphan” crops such as cassava do not receive much attention due to lack of commercial markets or low profitability. However, they are extremely important for human subsistence. This work emphasizes improvement of cassava, which is important for food security of smallholder farmers in developing economies. The “Golden” Cassava being developed as part of the BioCassava Plus program will contain enough beta-carotene, which the human body uses to make Vitamin A, to significantly combat the results of malnutrition in Sub-Saharan Africa. A time course experiment was conducted under greenhouse conditions for wild type cassava plants and transgenic cassava expressing introduced genes encoding deoxyxylulose-5-phosphate synthase (DXS) and phytoene synthase (CrtB). Transgenic cassava at different time points of root growth resulted in total carotenoids ranging up to 76-86 µg/g DW while wild type cassava produce low levels of total carotenoids ranging from 0.9-2.0 µg/g DW. Change in expression levels of other genes in the isoprenoid biosynthetic  pathway in response to the accumulation of beta-carotene and expression of DXS and CrtB will be discussed.