title: Genetic variation of γ-tocopherol methyltransferase gene contributes to elevated α-tocopherol content in soybean seeds.
abstract: BACKGROUND
  Improvement of α-tocopherol content is an important breeding aim to increase the nutritional value of crops. Several efforts have been conducted to improve the α-tocopherol content in soybean [Glycine max (L.) Merr.] through transgenic technology by overexpressing genes related to α-tocopherol biosynthesis or through changes to crop management practices. Varieties with high α-tocopherol content have been identified in soybean germplasms. The heritability of this trait has been characterized in a cross between high α-tocopherol variety Keszthelyi Aproszemu Sarga (KAS) and low α-tocopherol variety Ichihime. In this study, the genetic mechanism of the high α-tocopherol content trait of KAS was elucidated.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Laboratory of Plant Genetics and Evolution, Graduate School of Agriculture, Hokkaido University, Kita 9 Nishi 9, Sapporo 060-8589, Hokkaido, Japan.
authors: Maria S
authors: MS
authors: Dwiyanti
authors: Tetsuya
authors: T
authors: Yamada
authors: Masako
authors: M
authors: Sato
authors: Jun
authors: J
authors: Abe
authors: Keisuke
authors: K
authors: Kitamura
mesh_terms: D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005838:Genotype; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic; D040641:Quantitative Trait Loci; D012639:Seeds / Q000737:chemistry*; D030262:Soybean Proteins / Q000235:genetics / Q000378:metabolism*; D013025:Glycine max / Q000201:enzymology / Q000235:genetics*; D024502:alpha-Tocopherol / Q000032:analysis*
chemical_list: D018744:DNA, Plant; D030262:Soybean Proteins; D008780:Methyltransferases; C047259:gamma-tocopherol methyltransferase; D024502:alpha-Tocopherol