Cyanogenesis in cassava and its molecular manipulation for crop improvement

Abstract

While cassava is one of the most important staple crops worldwide, it has received the least investment per capita consumption of any of the major global crops. This is in part due to cassava being a crop of subsistence farmers that is grown in countries with limited resources for crop improvement. While its starchy roots are rich in calories, they are poor in protein and other essential nutrients. In addition, they contain potentially toxic levels of cyanogenic glycosides which must be reduced to safe levels before consumption. Furthermore, cyanogens compromise the shelf life of harvested roots due to cyanide-induced inhibition of mitochondrial respiration, and associated production of reactive oxygen species that accelerate root deterioration. Over the past two decades, the genetic, biochemical and developmental factors that control cyanogen synthesis, transport, storage, and turnover have largely been elucidated. It is now apparent that cyanogens contribute substantially to whole plant nitrogen metabolism and protein synthesis in roots. The essential role for cyanogens in root nitrogen metabolism, however, has confounded efforts to create acyanogenic varieties. This review proposes alternate molecular approaches that integrate accelerated cyanogen turnover with nitrogen reassimilation into root protein that may offer a solution to creating a safer, more nutritious cassava crop.

Breeding for postharvest physiological deterioration in cassava: problems and strategies

“…CYP79D1 and CYP79D2 encode for enzymes that hydroxylates valine (95%) and isoleucine (5%) to form the N-hydroxyl derivative, linamarin, a toxic cyanogenic glucoside (Schmidt et al 2018). Cyanogenic glycosides shorten the shelf-life of harvested cassava storage roots via cyanide inhibition of mitochondrial respiration, and associated cellular production of ROS that accelerates PPD (McMahon et al 2022). More recently, transgenic cassava lines with silenced MeAPL3 gene displayed a substantial decrease in storage root starch and dry matter contents.…”

De novo genome assembly of white clover (Trifolium repens L.) reveals the role of Copy Number Variation in rapid environmental adaptation

“…After demonstrating the existence of both Ac and Li CNVs in all three white clover whole genomes, we sought to test the hypothesis that CNVs at the Ac and Li loci directly affect the cyanogenesis phenotype. To do this, we focused on the Ac locus because synthesis of cyanogenic glucosides, mediated by the Ac gene cluster, is predicted to be directly correlated with the cyanogenic response [37]. We performed qPCR of genomic DNA and mRNA to estimate the correlation between CNV counts and expression in the Ac gene cluster (CYP79D15, CYP736A187, UGT85K17).…”

The Cyanogenic Potential of Certain Cassava Varieties in Uganda and Their Fermentation-Based Detoxification

“…The physiology and the biochemistry of cyanogenesis (Figure 1) in cassava have been well studied [14,15]. Cyanogenesis in cassava starts when there is damage in the plant tissue.…”

“…Cyanogenesis in cassava starts when there is damage in the plant tissue. When the vacuole is raptured, linamarin is released, and it is hydrolyzed by a cell wall-associated β-glycosidase, linamarase [14]. Linamarin hydrolyzes producing an unstable hydroxynitrile intermediate, acetone cyanohydrin, and glucose.…”