Genetic analysis of high α-tocopherol content in soybean seeds

Tocopherols, known as members of vitamin E, are the major lipophilic antioxidants in soybean. Since soybean seeds contain a low concentration of alpha-tocopherol (alpha-Toc), the tocopherol isoform with the highest vitamin E activity, some breeding efforts have been implemented to increase the alpha-tocopherol content in the seeds. In the present study, we used F-2 seed and F-2 plant (173 seeds) populations derived from a cross between a variety with a high alpha-tocopherol content, Keszthelyi A.S. (alpha-Toc 20-30%) and a Japanese cultivar, Ichihime (alpha-Toc < 10%) for genetic analysis of the high alpha-tocopherol concentration. There was no significant correlation between the alpha-tocopherol and total tocopherol contents in the F-2 plant (173 seeds) population, suggesting that the alpha-tocopherol and total tocopherol contents were regulated independently in the seeds. Therefore, it may be possible to increase the alpha-tocopherol concentration without affecting the total tocopherol content. Broad-sense heritability value for the alpha-tocopherol concentration trait was estimated to be 0.645 in the F-2 seeds, suggesting that the gamma-tocopherol concentration trait was highly heritable. Chi-square goodness-of-fit test for evaluating the relationship between genotype of certain SSR markers and the alpha-tocopherol concentration showed that the Sat_243 and Sat_167 markers (linkage group K) were significantly associated with the alpha-tocopherol concentration (P < 0.05). These markers could be used for marker-assisted selection to breed soybean cultivars with high alpha-tocopherol concentrations. Analysis of the F-2 seeds and the F-2 plants (173 seeds) for tocopherol composition showed that there was a significantly negative correlation between the alpha-tocopherol and gamma-tocopherol concentrations, suggesting that the activity of gamma-tocopherol methyltransferase, the enzyme that converts gamma-tocopherol to alpha-tocopherol, is high in individuals with a high alpha-tocopherol concentration.