Constitutive overexpression of Qui-Quine starch gene simultaneously improves starch and protein content in bioengineered Cassava (Manihot Esculenta Crantz)

Authors: HANKOUA, BERTRAND - Delaware State University; DIAO, MARIEME - Reckitt Benckiser, Inc; LIGABA-OSENA, AYALEW - University Of North Carolina Greensboro; Garcia, Rafael; HARUN, SARAHANI - Universiti Kebangsaan Malaysia; AHLAWAT, YOGESH - Chitkara University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cassava is a root crop that is a critical staple for large populations in sub-Saharan Africa; for very poor segments of the population cassava may be the only food available. On its own, cassava does not contain enough protein to sustain good health. Past efforts to increase cassava protein content have been unsatisfactory. This study demonstrates the successful application of a novel genetic engineering approach which results in cassava plants that accumulate increased protein and carbohydrate in their roots and leaves. The results suggest that this technique can be applied to improve the individual varieties of cassava grown in different regions.

Technical Abstract: Cassava serves as a crucial source of daily calorie intake for millions of people in sub-Saharan Africa (SSA), providing starch but lacking protein, leading to significant mortality and illness among impoverished populations in developing nations who rely solely on this crop for sustenance. Despite numerous attempts utilizing both traditional and biotechnological methods, efforts to address protein deficiency in cassava have met with little success. Our objective is to leverage modern technologies to enhance the nutritional value of cassava, thus improving the health outcomes of millions of consumers through the creation of genetically engineered cassava strains with elevated protein content. In this study, we utilized Qui-Quine Starch (QQS), a novel orphan gene unique to Arabidopsis thaliana, to develop transgenic cassava plants with increased protein accumulation in their tissues. QQS functions as a transcription factor, influencing the allocation of carbon and nitrogen within plants, thereby impacting the levels of protein, carbohydrates, and even oils when expressed heterologously in transgenic plants. A total of 10 transgenic cassava lines expressing QQS were successfully regenerated in this study, among which line R7 (F) demonstrated superior growth vigor. Expression of QQS gene in the transgenic lines was verified by quantitative RT- PCR. Our findings reveal that heterologous expression of the QQS gene into cassava plant increased leaf protein content by 36% in line R’’’ (LA) L2 and root protein by 17% for the same line compared to their wild- type control plants and the empty vector control. Moreover, leaf soluble total carbohydrate increased by 51.76% in line R (G) L2 and root soluble total carbohydrate increased by 46.75% in line R7 (F). The novel function of QQS in increasing the starch content in the transgenic biomass is demonstrated in the study. No significant change in the content of specific amino acids was observed among the lines and various plant parts. In addition, QQS expression revealed an increase in biomass, plant vigor, and early In vitro mini-tubers production for line R7 (F). However, it will be very critical to validate the observed changes in nutritional profiles of these young cassava plants expressing QQS by biochemically profiling these plants at maturity, especially once these novel matured cassava plants expressing the QQS are established in the field. Gene interaction study between AtQQS and 59 interacting partners, generated 184 interactions or edges. Most of this established gene network consisted of several functional categories related to the regulation of the starch metabolic process and the regulation of the auxin biosynthetic process. As this study validated the role of QQS in transgenic cassava plant cv60444 in imparting starch and protein content, the transferability of this technology to consumer-preferred plant parts (tuberous roots and leaves) of economically important cassava cultivars and local landraces grown by many farmers in SSA is the next logical step which should be attempted. This is the first biotechnological report demonstrating a simultaneous increase of starch and protein content in bioengineered cassava overexpressing a transcription factor modulating biochemical and physiological processes.