Cassava, a staple crop for about 40% of Africans, is a starchy tuber that can prevail in poor soils and despite drought. However, cassava produces toxic compounds, especially in conditions with little water. This is especially concerning in the face of global warming.

Cassava naturally contains cyanogenic glucosides, which are converted into cyanide as they are processed by the human body. The tuber can be treated after harvesting to eliminate cyanogenic glucosides, but existing processing methods can take days to complete. Industrial systems for removing the cyanide from cassava also spark health and environmental concern, as contaminants can enter surrounding air and water. If processing is not available, the subsequent exposure to cyanide in significant quantities poses serious health risks, especially in those with diets low in protein. Even in commercial products, cyanide levels have been detected above recommendations set by the World Health Organization, emphasizing the prevalence of this issue. Especially in regions especially affected by food insecurity, decreasing the barriers to food access is critical, so researchers set out to decrease cyanogen concentrations in raw cassava.

In cassava, cyanogenic glucoside production is started by two enzymes, CYP79D1 and CYP79D2. Using CRISPR/Cas9 and Agrobacterium, researchers knocked out the genes encoding these enzymes in two popular cultivars, along with a variety engineered for resistance to cassava mosaic disease from previous research. To investigate the roles of each gene, they made mutants with various combinations of edits to the genes. They found that one of the enzymes, CYP79D2, resulted in a greater reduction in cyanogenic glucoside when disabled (by a factor of 3-10), but editing both made a staggering difference. In the two popular cassava varieties, they recorded the abundances of linamarin (the cyanogenic glucoside that makes up over 90% of cassava’s cyanogens) in the leaves. In the lines with both genes knocked out, they found no linamarin in the leaves. This dramatic reduction was reflected across all three cultivars tested, both in cyanogenic glucosides and evolved cyanide, and in both leaves and roots. Additionally, disrupting these genes did not have a substantial impact on crop appearance, as all types were visually indistinguishable.

Outside of human consumption, cyanogens might play other roles. They are thought to initiate the production of reactive oxygen species in harvested tubers, which leads to their deterioration, so their removal could possibly lengthen the shelf life of cassava. However, it has been considered that cyanogen elimination might negatively impact protein synthesis. Cyanogens are hypothesized to play an important role in the production of proteins by transporting reduced nitrogen to the roots. If this is the case, though, increasing nitrogen reductase activity might make up for the loss. However, when researchers grew the knockouts with no detected cyanogens in a low-nitrogen environment, they did not observe a difference between the wild types under the same conditions. Further research on this pathway is required to make a definitive conclusion on the implications of these mutant lines, however these findings are optimistic for their success.

I covered a type of GM cassava last August, and little did I know my current PI at the Danforth Center, Dr. Nigel Taylor, worked on that very project! His lab, though it also focuses on other plants, is mostly known for cassava, so I wanted to familiarize myself with its more recent research. Even though I’m not on this project, I am definitely curious about it, and I still get to work with cassava plants through micropropogation and whatnot here and there.

The main reason I chose this article in particular, though, is it’s also a featured publication for the Plant Genomics and Transformation Facility at the Innovative Genomics Institute. AKA my future PI is on this paper as well, how cool is that!? It’s almost like the researchers I’m interested in are doing research I’m interested in…

I remember developing a serious distaste for summarizing scientific articles over the course of my mosquito projects, but these last few papers have been really enjoyable to cover. I’m not sure if I’ve developed as a reader, or I just know more about this subject, or maybe these specific articles happen to be written in a more digestable manner, but I’m very excited to be learning a lot about these projects without having to spend ten hours reading each paper, and another five writing about it. Ya girl just doesn’t have time for that every week!

One of the great things about entering the research world is following different labs, so instead of aimlessly looking for news in genetically modified organisms, I can read the publications of my favorite researchers. It tells me what they’re up to and gives me questions to ask them, which is an opportunity I won’t have forever. It does take a considerable amount of time, but I’d like to cover more papers like these so I can talk to the PIs at the Danforth Center about them before I leave. What an exciting opportunity. Stay tuned to learn with me!

https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1079254/full