Doctor of Philosophy
Date of Defense
Cassava (Manihot esculenta Crantz.) is a member of the Euphorbiaceae family, cultivated in the tropics and subtropical areas as a staple food crop for more than 700 million people around the world. The starchy storage roots of cassava are rich in calories and deficient in all other nutrients, cassava meals has the lowest of all sources of dietary protein. Severe protein deficiencies and malnutrition problems are common among those who rely on cassava as their daily meal. Although cassava is ranked the fifth most important crop in the world, the research on this crop is very limited. Among the limited number of reports on cassava genetic transformation, only one attempt was concerned in nutritional enhancement of cassava storage roots. In this thesis, methodologies of improving the protein content in cassava storage roots are demonstrated. I investigated the possibility of accumulating storage proteins and studied the limitation of this process in the storage roots of cassava. Tissue and subcellular-targeted protein expressions are found to concentrate the expressed proteins and improve the amino acid profile in cassava storage roots. Fusing targeting signal peptides, which stabilize the expressed proteins in protective subcellular environments, enhances the storage protein accumulation in cassava root cells. In addition, establishing a strong protein sink in the storage roots redirects the nitrogen flow from cyanogen biosynthesis towards the protein synthesis machinery. On the other hand, the ability to increase the protein content indirectly by modifying metabolic pathways, such as the pro-vitamin A pathway, illustrates the huge potential of cassava and the wealth of its genetic resources. I also clearly demonstrated that protein accumulation in the roots and pro-Vitamin A enhancement are inducing a number of changes in several biochemical pathways. All these modifications have been tested in field trials, where transgenic plants are evaluated for their phenotype and yield productivity. The objective of all the experiments performed in this study is to increase the protein content in cassava storage roots and provide solutions to the malnutrition problems for those who cannot afford to supplement their cassava meals with other nutritious foods.
Abhary, Mohammad, "Development of a methodology to attain high levels of storage proteins in cassava tuberized roots and its implications" (2010). Dissertations. 446.