Metabolic engineering of soybean seeds for enhanced vitamin E tocochromanol content and effects on oil antioxidant properties in polyunsaturated fatty acid-rich germplasm |
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Affiliation: | 1. Departamento de química, Universidade Estadual de Londrina Rodovia Celso Garcia Cid, PR 445, Km 380, Campus Universitário Cx. Postal 6001 CEP 86055-900 Londrina, PR, Brazil;2. EMBRAPA-Centro Nacional de Pesquisa de Soja (CNPSo), Caixa Postal 231, CEP 86001-970 Londrina, PR, Brazil;3. Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, CEP 87020-900, Maringá, Paraná, Brazil;4. Departamento de química, Universidade Tecnológica Federal do Paraná, Rua Marcílio Dias, 635, CEP 86812-460, Apucarana, Paraná, Brazil;1. USDA-ARS, Crop Genetics Research Unit, Jackson, TN, USA;2. USDA-ARS, Crop Production Systems Research Unit, Jackson, TN, USA |
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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, 18:4Δ6,9,12,15)-producing line, resulting in progeny with oil enriched in SDA and α- or γ-linoleic acid (ALA, 18:3Δ9,12,15 or GLA, 18:3Δ6,9,12), 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. |
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Keywords: | Vitamin E Tocochromanol Tocopherol Tocotrienol Oilseed Antioxidant Homogentisate geranylgeranyl transferase Soybean HGGT" },{" #name" :" keyword" ," $" :{" id" :" kwrd0055" }," $$" :[{" #name" :" text" ," _" :" homogentisate geranylgeranyl transferase HPT" },{" #name" :" keyword" ," $" :{" id" :" kwrd0065" }," $$" :[{" #name" :" text" ," _" :" homogentisate phytyltransferase γ-TMT" },{" #name" :" keyword" ," $" :{" id" :" kwrd0075" }," $$" :[{" #name" :" text" ," _" :" γ-tocopherol/tocotrienol methyltransferase ALA" },{" #name" :" keyword" ," $" :{" id" :" kwrd0085" }," $$" :[{" #name" :" text" ," _" :" α-linolenic acid GLA" },{" #name" :" keyword" ," $" :{" id" :" kwrd0095" }," $$" :[{" #name" :" text" ," _" :" γ-linolenic acid SDA" },{" #name" :" keyword" ," $" :{" id" :" kwrd0105" }," $$" :[{" #name" :" text" ," _" :" stearidonic acid PUFA" },{" #name" :" keyword" ," $" :{" id" :" kwrd0115" }," $$" :[{" #name" :" text" ," _" :" polyunsaturated fatty acid |
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