Cassava (Manihot esculenta Crantz) is an important tropical crop which provides a large portion of daily calories intake to hundreds of millions of people in Africa, Latin America, and tropical Asia. Cassava is grown for its starchy storage roots as staple food, as animal feed, and as industrial raw material. The utilisation of cassava is hindered by its characteristic physiological response, the post-harvest physiological deterioration (PPD). The inevitable wounding caused during harvesting and handling will trigger a series of physiological responses within 24 to 48 hours, which causes a blue-black discoloration in the storage roots, rendering these roots unmarketable and unpalatable in a few days. During the PPD response large amount of phenylpropanoid compounds, especially scopoletin and its glycoside, accumulate in the roots. Scopoletin may play an important role in PPD development but little work has been done on the possible relationship. Here we aim to examine the effects of altering scopoletin synthesis in cassava roots on the PPD response.In Arabidopsis thaliana, gene F6’H1 (feruloul CoA 6’-hydroxylase 1) is indispensable in the biosynthesis of scopoletin. Cassava F6’H1 candidate gene family involved in scopoletin synthesis were identified by their ability to functionally complement F6’H1 T-DNA insertion mutation in Arabidopsis thaliana that prevented synthesis of scopoletin. RNAi constructs targeting the identified cassava F6’H1 candidate gene family were designed, under the control of either constitutive CaMV 35S or root-specific StPAT promoters. These were used to transform wild-type cassava to down-regulate the expression of these scopoletin synthetic genes in F6’H1 gene family. The inhibition of cassava F6’H1 candidate gene expression and thus the scopoletin synthesis in transgenic cassava roots were confirmed by qRT-PCR and LC-MS, respectively. The RNAi transgenic cassava lines show less scopoletin accumulation and inhibited F6’H1 candidate genes expression during the PPD response. A reduced PPD discoloration development compared to that of the wild-type was also observed in the RNAi transgenic cassava lines.
|Date of Award||11 Jan 2017|
|Supervisor||John Beeching (Supervisor) & James Doughty (Supervisor)|