Abstract
BackgroundSoybean is one of the most important crop sources of tocopherols (Toc). However, the content of α-Toc, an isoform with the highest vitamin E activity in humans, is low in most cultivars. With the aim of broadening genetic variability, we performed quantitative trait locus (QTL) analysis for a high seed α-Toc trait detected in a wild soybean and characterized the sequence polymorphisms and expression profiles of γ-tocopherol methyltransferase (γ-TMT) genes as potential candidates.ResultsA recombinant inbred line population was developed from a cross between the low α-Toc breeding line TK780 and the high α-Toc wild accession B04009. The α-Toc content in seeds correlated strongly with the ratio of α-Toc to γ-Toc contents. QTL analysis using a high-density map constructed with 7710 single nucleotide polymorphisms (SNPs) generated by restriction site-associated DNA sequencing detected six QTLs involved in α-Toc biosynthesis. Of these, three in chromosomes (Chr) 9, 11, and 12 produced consistent effects during a 2-year trial. B04009 allele at QTLs in Chr9 and Chr12 and TK780 allele at the QTL in Chr11 each promoted the conversion of γ-Toc to α-Toc, which elevated the seed α-Toc content. SNPs and indels were detected between the parents in three γ-TMT genes (γ-TMT1, γ-TMT2, and γ-TMT3) co-located in the QTLs in Chr9 and Chr12, of which some existed in the cis-regulatory elements associated with seed development and functions. In immature cotyledons, γ-TMT3 was expressed at higher levels in B04009 than TK780, irrespective of two thermal conditions tested, whereas the expression of γ-TMT2 was markedly upregulated under higher temperatures, particularly in B04009.ConclusionsWe identified QTLs consistently controlling α-Toc biosynthesis in wild soybean seeds in 2-year trials. The QTL on Chr9 had been previously identified in soybean, whereas the QTLs on Chr11 and Chr12 were novel. Further molecular dissections and characterization of the QTLs may facilitate the use of high α-Toc alleles from wild soybean in soybean breeding and an understanding of the molecular mechanisms underlying α-Toc biosynthesis in soybean seeds.
Highlights
Soybean is one of the most important crop sources of tocopherols (Toc)
Tocopherol contents and ratios of parental soybean lines under different thermal conditions Toc contents and compositions were compared between seeds matured at 20 °C and 30 °C, and TK780 and B04009 were shown to have different seed Toc biosynthesis characteristics
TK780 produced seeds with tocopherol contents approximately two-fold higher than B04009, irrespective of the temperature during seed development (Table 1)
Summary
Soybean is one of the most important crop sources of tocopherols (Toc). There are four isoforms of tocopherols, α-, β-, γ-, and δ-tocopherol, of which α-tocopherol (α-Toc) has the highest vitamin E activity in humans because of its highest affinity with the hepatic tocopherol transfer protein [1, 2]. As well as vitamin E activity, α-Toc plays a Soybean (Glycine max Merr.) is one of the most important agricultural crops worldwide because it is a major source of oil, protein, starch, dietary fiber, minerals, and vitamins, and is used as a material in the production of biodiesel, feed, and cosmetics. Considering that soybean is a major oil source providing 30% of the total worldwide oil consumption, increasing the seed α-Toc
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