Genetic variation of γ-tocopherol methyltransferase gene contributes to elevated α-tocopherol content in soybean seeds

Through QTL analysis and fine mapping in populations from a cross between KAS and a Japanese variety Ichihime, we identified γ-TMT3, which encodes γ-tocopherol methyltransferase, as a candidate gene responsible for high α-tocopherol concentration in KAS. Several nucleotide polymorphisms including two nonsynonymous mutations were found in the coding region of γ-TMT3 between Ichihime and KAS, but none of which was responsible for the difference in α-tocopherol concentration. Therefore, we focused on transcriptional regulation of γ-TMT3 in developing seeds and leaves. An F5 line that was heterozygous for the region containing γ-TMT3 was self-pollinated. From among the progeny, plants that were homozygous at the γ-TMT3 locus were chosen for further evaluation. The expression level of γ-TMT3 was higher both in developing seeds and leaves of plants homozygous for the γ-TMT3 allele from KAS. The higher expression level was closely correlated with high α-tocopherol content in developing seeds. We generated transgenic Arabidopsis plants harboring GUS gene under the control of γ-TMT3 promoter from KAS or Ichihime. The GUS activity assay showed that the activity of γ-TMT3 promoter from KAS was higher than that of Ichihime.The genetic variation in γ-TMT3, which plays a major role in determining α-tocopherol concentration, provides significant information about the regulation of tocopherol biosynthesis in soybean seeds. This knowledge will help breeding programs to develop new soybean varieties with high α-tocopherol content.The vitamin E family comprises tocopherols (α, β, γ, and δ forms) and tocotrienols (α, β, γ, and δ forms). All isoforms possess lipid antioxidant activity, and α-tocopherol possesses the highest vitamin E activity in mammals [1,2]. Vitamin E is widely used as an antioxidant in foods and oils, as a nutrient additive in poultry and cattle feeds to improve meat quality, and as a supplement in the human diet to help prevent diseases such as cancer and cardiovasc