Metabolic engineering of soybean seeds for enhanced vitamin E tocochromanol content and effects on oil antioxidant properties in polyunsaturated fatty acid-rich germplasm

Anji Reddy Konda; Tara J Nazarenus; Hanh Nguyen; Junsi Yang; Malleswari Gelli; Samantha Swenson; Jamie M Shipp; Monica A Schmidt; Rebecca E Cahoon; Ozan N Ciftci; Chunyu Zhang; Tom Elmo Clemente; Edgar B Cahoon

doi:10.1016/j.ymben.2019.10.005

Metabolic engineering of soybean seeds for enhanced vitamin E tocochromanol content and effects on oil antioxidant properties in polyunsaturated fatty acid-rich germplasm

Metab Eng. 2020 Jan:57:63-73. doi: 10.1016/j.ymben.2019.10.005. Epub 2019 Oct 23.

Authors

Affiliations

¹ Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA; Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA.
² Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA; Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA.
³ Department of Food Science and Technology, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA.
⁴ Systems and Innovations for Breeding and Seed Products, Corteva Agriscience, Johnston, IA, 50131, USA.
⁵ USDA-ARS Plant Genetics Research Unit, Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, Missouri, 63132, USA.
⁶ National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China.
⁷ Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA; Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA. Electronic address: ecahoon2@unl.edu.

PMID: 31654815
DOI: 10.1016/j.ymben.2019.10.005

Abstract

Soybean seeds produce oil enriched in oxidatively unstable polyunsaturated fatty acids (PUFAs) and are also a potential biotechnological platform for synthesis of oils with nutritional omega-3 PUFAs. In this study, we engineered soybeans for seed-specific expression of a barley homogentisate geranylgeranyl transferase (HGGT) transgene alone and with a soybean γ-tocopherol methyltransferase (γ-TMT) transgene. Seeds for HGGT-expressing lines had 8- to 10-fold increases in total vitamin E tocochromanols, principally as tocotrienols, with little effect on seed oil or protein concentrations. Tocochromanols were primarily in δ- and γ-forms, which were shifted largely to α- and β-tocochromanols with γ-TMT co-expression. We tested whether oxidative stability of conventional or PUFA-enhanced soybean oil could be improved by metabolic engineering for increased vitamin E antioxidants. Selected lines were crossed with a stearidonic acid (SDA, 18:4^Δ6,9,12,15)-producing line, resulting in progeny with oil enriched in SDA and α- or γ-linoleic acid (ALA, 18:3^Δ9,12,15 or GLA, 18:3^Δ6,9,12), from transgene segregation. Oil extracted from HGGT-expressing lines had ≥6-fold increase in free radical scavenging activity compared to controls. However, the oxidative stability index of oil from vitamin E-enhanced lines was ~15% lower than that of oil from non-engineered seeds and nearly the same or modestly increased in oil from the GLA, ALA and SDA backgrounds relative to controls. These findings show that soybean is an effective platform for producing high levels of free-radical scavenging vitamin E antioxidants, but this trait may have negative effects on oxidative stability of conventional oil or only modest improvement of the oxidative stability of PUFA-enhanced oil.

Keywords: Antioxidant; Homogentisate geranylgeranyl transferase; Oilseed; Soybean; Tocochromanol; Tocopherol; Tocotrienol; Vitamin E.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Fatty Acids, Unsaturated* / biosynthesis
Fatty Acids, Unsaturated* / genetics
Gene Expression Regulation, Plant*
Glycine max* / genetics
Glycine max* / metabolism
Metabolic Engineering*
Seeds* / genetics
Seeds* / metabolism
Soybean Oil / biosynthesis
Soybean Oil / genetics
Vitamin E* / biosynthesis
Vitamin E* / genetics

Substances

Fatty Acids, Unsaturated
Vitamin E
Soybean Oil