Trait stacking simultaneously enhances provitamin a carotenoid and mineral bioaccessibility in biofortified sorghum bicolor

Authors: Dzakovich, Michael; DEBELO, HAWI - North Carolina State University; ALBERTSEN, MARC - Corteva Agriscience; CHE, PING - Corteva Agriscience; JONES, TODD - Corteva Agriscience; SIMON, MARISSA - Corteva Agriscience; ZHAO, ZUO-YU - Corteva Agriscience; GLASSMAN, KIMBERLY - Corteva Agriscience; FERRUZZI, MARIO - Arkansas Children'S Nutrition Research Center (ACNC)

Submitted to: bioRxiv
Publication Type: Other
Publication Acceptance Date: 8/5/2022
Publication Date: 8/5/2022
Citation: Dzakovich, M.P., Debelo, H., Albertsen, M., Che, P., Jones, T., Simon, M., Zhao, Z., Glassman, K., Ferruzzi, M. 2022. Trait stacking simultaneously enhances provitamin a carotenoid and mineral bioaccessibility in biofortified sorghum bicolor. bioRxiv. https://doi.org/10.1101/2022.08.03.501587.
DOI: https://doi.org/10.1101/2022.08.03.501587

Interpretive Summary: Diets of people living in sub-Saharan Africa are often dominated by cereal grains, like sorghum, that lack sufficient vitamins and minerals. As a result, people in this region suffer from chronic diseases related to not getting enough vitamin A, iron, or zinc. Biofortification efforts to increase provitamin A carotenoids and reduce antinutrients like phytic acid that prevent minerals such as iron and zinc from being absorbed, have been tested in sorghum, but not simultaneously. Additionally, there is an established trade-off between how much provitamin A carotenoids are absorbed vs mineral elements reported in the literature. We created genetically engineered sorghum plants that have drastically higher amounts of provitamin A carotenoids as well as an enzyme (phytase) that breaks down phytic acid. Activating phytase significantly improved estimates of mineral absorption and did not negatively impact provitamin A carotenoid absoption. Porridges made from these sorghum plants would be able to provide both higher amounts of provitamin A carotenoids, iron, and zinc compared to typical cultivars. Our findings represent represent an important step forward to providing people in sub-Saharan Africa with crops that better meet their nutritional needs. Additionally, our study challenges the current dogma that higher concentrations of mineral elements will impact that amount of provitamin A carotenoids that can be absorbed. The sorghum varieties that we developed can also be used to test basic nutritional questions using animal or human studies.

Technical Abstract: Vitamin A, iron, and zinc deficiencies are major nutritional inadequacies in sub- Saharan Africa and disproportionately affect women and children. Biotechnology strategies have been tested to individually improve provitamin A carotenoid or mineral content and/or bio-accessibility in staple crops including sorghum (Sorghum bicolor ). However, concurrent carotenoid and mineral enhancement has not been thoroughly assessed and antagonism between these chemical classes has been reported. This work evaluated two genetically engineered constructs containing a suite of heterologous genes to increase carotenoid stability and pathway flux, as well as phytase to catabolize phytate and increase mineral bio-accessibility. Kernels from transformed sorghum events were processed into model porridges and evaluated for carotenoid and mineral content as well as bio-accessibility. Transgenic events produced markedly higher amounts of carotenoids (26.4 µg/g) compared to null segregants (4.2 µg/g) and wild-type control (Tx430; 3.7 µg/g). A 200 g serving of porridge made with these transgenic events represents a projected 53.7% of a 4–8-year-old child’s vitamin A estimated average requirement. Phytase activation by pre-steeping flour resulted in significant phytate reduction (9.4 to 4.2 mg/g), altered the profile of inositol phosphate metabolites, and reduced molar ratios of phytate to iron (16.0 to 4.1); and zinc (19.0 to 4.9) in engineered material; suggesting improved mineral bio-accessibility. Improved phytate: mineral ratios did not significantly affect micellization and bio-accessible provitamin A carotenoids were over 2300% greater in transgenic events compared to corresponding null segregants and wild-type controls. These data suggest that combinatorial approaches to enhance micronutrient content and bio-accessibility are feasible and warrant further assessment in human studies.