RNAi-Mediated Downregulation of Cyano-Glycoside Biosynthesis in Kenyan Cassava (Manihot esculenta Crantz) Genotypes

Abstract

Cassava (Manihot esculenta Crantz) is an important perennial tropical crop for millions of people globally, particularly in sub- Saharan Africa. It is preferred due to its agronomical attributes such as ability to grow in poor soils and drought resistance. Cassava storage roots are a good source of starch. Further, cassava leaves and shoots are eaten as vegetables and are an excellent source of vitamins, minerals and protein. Cassava is also used in the production of ethanol for fuel, animal feed, and as a raw material for the starch industry. Cassava has high photosynthetic rates and its roots can persist in the soil for 8-24 months without decaying, thereby making it an ideal food security crop. In Kenya, cassava is a major source of subsistence and cash income to farmers in agroclimatically- disadvantaged regions and high potential areas of coast, Central and Western regions of Kenya. Sadly, cassava leaves and roots contain potentially toxic levels of cyanogenic glycosides. Cassava is largely propagated clonally making it an ideal plant for improvement through genetic engineering. This study was designed to produce transgenic acyanogenic cassava plants in which the expression of the cytochrome P450 genes (CYP79D1/D2) is downregulated through RNAi. Three Kenyan cassava genotypes; Adhiambo lera, Kibanda meno and Serere along with an exotic model cultivar TMS 60444 were used. The transformable lines were then taken through Agrobacterium-mediated transformation with an RNAi cassette harbouring cytochrome P450 genes (CYP92D1) to down regulate production of cyanoglycosides. Molecular analysis by PCR and RT-PCR confirmed transformation of the putative transformants.