Eliminating Cyanoglucosides from Cassava Tubers: Exploiting The Endogenous Turnover and Transporters

International Journal of Research and Innovation in Applied Science (IJRIAS) | Volume VI, Issue VI, June 2021|ISSN 2454-6194

Eliminating Cyanoglucosides from Cassava Tubers: Exploiting The Endogenous Turnover and Transporters

Samson Ugwuanyi*¹; Chika C. Nwadinigwe²; Chidiebere A. Adeosun³ and Hannah I⁴. Iwuoha^5
1,⁵Department of Plant Breeding, Justus Liebig University, Giessen, Germany.
²,³,⁴Department of Plant Science and Biotechnology, University of Nigeria, Nsukka, Nigeria.
Corresponding author

Abstract: Cassava (Manihot esculenta Crantz) is a major staple food in sub-Saharan Africa. Its efficient utilization for food is affected by the presence of cyanoglucosides in the tubers. Following the mapping of CYP79D1/D2 genes involved in the cyanoglucosides biosynthesis, the last two decades have witnessed intense research to develop cassava plants with insignificant level of cyanoglucosides via gene silencing. These concerted efforts are yet to produce satisfactory outcomes. However, research has revealed roles of cyanoglucosides in important metabolic pathways in cassava. Therefore, an alternative direction must be sought to conserve the functions of these metabolites while eliminating the compounds from the edible tubers. The endogenous turnover and transport pathways of cyanoglucosides could be interesting areas for future research. It is expected that the upregulation of the genes involved in the turnover pathway would result in increased synthesis of these turnover products, which would subsequently be incorporated into primary metabolism; thereby avoiding the accumulation of cyanoglucosides in the tubers. Similarly, the characterization of glucosinolate transporters in Arabidopsis presents an avenue to study the mechanisms and roles of transporters of defense compounds such as cyanoglucosides in cassava. Research has shown that the metabolic engineering of these compounds are possible by interfering with the expression of transport molecules, and holds the potential for developing plants with reduced accumulation of toxic compounds in the edible tissues or plant parts. The objective of this study was to document recent literature and highlight pathways that involve turning cyanoglucosides into useful intermediates which could be exploited in developing cyanoglucosides-free cassava tubers.

Keywords: Cyanogenic glucosides, RNA interference, endogenous turnover

INTRODUCTION

Cassava (Manihot esculenta Crantz) is a major staple in the developing countries, ranked 4th most important crop behind maize, rice and sugarcane [1]. Cassava is an important food crop to a large part of the population in the sub-Saharan Africa and it is primarily cultivated for its tuberous roots, which provide more than half of the daily calorie intake in sub-Saharan Africa where more than 80% of the harvest is consumed [2,3]. Unfortunately, the presence of a significant amount of cyanogenic glucosides (CNglcs) in all parts of the cassava plant is the major limitation to its efficient use for food across the world [4]. In the last two decades, eliminating CNglcs has been a major research priority in cassava breeding programmes. Andersen et al. [4] mapped two cytochrome P450 genes: CYP79D1 and CYP79D2 involved in the CNglcs biosynthesis, triggered interests in the application of different molecular techniques to interfere with the expression of these genes. Several reports have been published but there is still more work to be done in this area. However, findings from several of these researches have added to the evidence of the roles played by CNglcs in important metabolic pathways in cassava,

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