Identification of quantitative trait loci for increased α-tocopherol biosynthesis in wild soybean using a high-density genetic map - PubMed (original) (raw)

Identification of quantitative trait loci for increased α-tocopherol biosynthesis in wild soybean using a high-density genetic map

Cheolwoo Park et al. BMC Plant Biol. 2019.

Abstract

Background: Soybean 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.

Results: A 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.

Conclusions: We 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.

Keywords: Functional food; Glycine max; Quantitative trait loci; Soybean; Tocopherol; Vitamin E; Wild germplasm.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Fig. 1

Tocopherol biosynthesis pathway. Enzymes are shown in green boxes. Phytyl-DP, phytyl-diphosphate; HGA, homogentisic acid; MPBQ, 2-methyl-6-phytyl-1,4-benzoquinol; DMPBQ, 2,3-dimethyl-6-phytyl-1,4-benzoquinol; MPBQMT, 2-methyl-6-phytyl-1,4-benzoquinol methyltransferase; TC, tocopherol cyclase; γ-TMT, γ_-_tocopherol methyltransferase

Fig. 2

Fig. 2

Tocopherol content variation in seeds in RILs of the cross between TK780 and B04009. Closed arrow: B04009, Open arrow: TK780.

Fig. 3

Fig. 3

Scatter diagrams showing relationship between seed α-Toc contents with total tocopherol (Toc) contents and Toc ratios in RILs of the cross between TK780 and B04009. Correlations between the seed α-Toc content and the total Toc contents in 2016 (a) and in 2017 (b). Correlations between the seed α-Toc contents and the (α + γ)/δ-Toc ratios in 2016 (c) and 2017 (d). The (α + γ)/δ-Toc ratio is the ratio of the sum of α- and γ-Toc contents to the total δ-Toc content. Correlations between the seed α-Toc content and the α/γ-Toc ratios in 2016 (e) and 2017 (f). The α/γ-Toc ratio is the ratio of the α-Toc content to the γ-Toc content. **, P < 0.01; ns, non-significant.

Fig. 4

Fig. 4

Variation in tocopherol ratios in seeds in RILs of the cross between TK780 and B04009. (α + γ)/total ratio: the ratio of the sum of α- and γ-Toc contents to the total Toc content. α/γ ratio: the ratio of the α-Toc content to the γ-Toc content. Closed arrow: B04009, Open arrow: TK780.

Fig. 5

Fig. 5

Location of QTLs for tocopherol contents and ratios in RILs of TK780 and B04009 cross

Fig. 6

Fig. 6

Additive effects of three QTLs for the seed α/γ ratio in RILs of the cross between TK780 and B04009. B04009 and TK780 are designated as WS and CS, respectively

Fig. 7

Fig. 7

Expression profiles of three γ-TMT genes in immature cotyledons matured in 20 °C and 30 °C. The immature cotyledons were obtained from plants grown under 20 °C and 30 °C. The relative expression is presented using actin (Glyma.18G222800.1) expression as an internal control. The experiments were repeated four times using independently synthesized cDNAs. Error bars; standard errors, Different alphabets indicate statistically significant (at 5% level) differences between mean values tested by Tukey’s HSD.

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