Biofortification of field-grown cassava by engineering expression of an iron transporter and ferritin

Authors: NARAYANAN, NARAYANAN - Danforth Plant Science Center; BEYENE, GETU - Danforth Plant Science Center; CHAUHAN, RAJ DEEPIKA - (NCE, CECR)networks Of Centres Of Exellence Of Canada, Centres Of Excellence For Commercilization A; GAITAN-SOLIS, ELIANA - Danforth Plant Science Center; GEHAN, JACKSON - Danforth Plant Science Center; BUTTS, PAULA - Danforth Plant Science Center; SIRITUNGA, DIMUTH - University Of Puerto Rico; OKWUONU, IHUOMA - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - Nigeria; WOLL, ARTHUR - Cornell University; JIMENEZ-AGUILAR, DULCE - Baylor College Of Medicine; BOY, ERICK - International Food Policy Researc Institute (IFPRI); Grusak, Michael; ANDERSON, PAUL - Danforth Plant Science Center; TAYLOR, NIGEL - Danforth Plant Science Center

Submitted to: Nature Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2018
Publication Date: 1/28/2019
Citation: Narayanan, N., Beyene, G., Chauhan, R., Gaitan-Solis, E., Gehan, J., Butts, P., Siritunga, D., Okwuonu, I., Woll, A., Jimenez-Aguilar, D.M., Boy, E., Grusak, M.A., Anderson, P., Taylor, N.J. 2019. Biofortification of field-grown cassava by engineering expression of an iron transporter and ferritin. Nature Biotechnology. 37:144-151. https://doi.org/10.1038/s41587-018-0002-1.
DOI: https://doi.org/10.1038/s41587-018-0002-1

Interpretive Summary: Cassava is an important root crop that serves as a staple food for human populations, especially in developing countries where food security is a concern. Cassava roots also contain low concentrations of iron and zinc, which can lead to micronutrient deficiencies in humans who consume this staple food. Scientists have looked for cassava varieties with higher levels of micronutrient minerals, but these have not been found. Therefore, to improve the nutritional value of this food source, we tested the impact of a biotech approach in which genes for iron transport or iron storage were transferred into cassava varieties. We found that the modified varieties not only absorbed and stored more iron in the storage root, but zinc levels were also increased. Additional tests to determine whether these minerals would be readily absorbed from cooked cassava products demonstrated a high level of mineral availability. These modified varieties, when consumed in quantities typical for certain African populations, could provide significant amounts of iron and zinc to children and women. This biotech approach with cassava could be used with other staple food crops to help alleviate micronutrient deficiencies in at-risk human populations.

Technical Abstract: Less than 10% of the estimated average requirement (EAR) for iron and zinc is provided by consumption of storage roots of the staple crop cassava (Manihot esculenta Crantz) in West African human populations. We used genetic engineering to improve mineral micronutrient concentrations in cassava. Overexpression of the Arabidopsis thaliana vacuolar iron transporter VIT1 in cassava accumulated three- to seven times-higher levels of iron in transgenic storage roots than nontransgenic controls in confined field trials in Puerto Rico. Plants engineered to coexpress a mutated A. thaliana iron transporter (IRT1) and A. thaliana ferritin (FER1) accumulated iron levels 7–18 times higher and zinc levels 3–10 times higher than those in nontransgenic controls in the field. Growth parameters and storage-root yields were unaffected by transgenic fortification in our field data. Measures of retention and bioaccessibility of iron and zinc in processed transgenic cassava indicated that IRT1 + FER1 plants could provide 40–50% of the EAR for iron and 60–70% of the EAR for zinc in 1- to 6-year-old children and nonlactating, nonpregnant West African women.