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This study aimed to discover the quantitative trait loci (QTL) associated with a high seed protein content in soybean and unravel the potential candidate genes. We developed two recombinant inbred line populations: YS and SI, by crossing Saedanbaek (high protein) with YS2035-B-91-1-B-1 (low protein) and Saedanbaek with Ilmi (low protein), respectively, and evaluated the protein content for three consecutive years. Using single-nucleotide polymorphism (SNP)-marker-based linkage maps, four QTLs were located on chromosomes 15, 18, and 20 with high logarithm of odds values (5.9–55.0), contributing 5.5–66.0% phenotypic variance. In all three experimental years, qPSD20-1 and qPSD20-2 were stable and identified in overlapping positions in the YS and SI populations, respectively. Additionally, novel QTLs were identified on chromosomes 15 and 18. Considering the allelic sequence variation between parental lines, 28 annotated genes related to soybean seed protein—including starch, lipid, and fatty acid biosynthesis-related genes—were identified within the QTL regions. These genes could potentially affect protein accumulation during seed development, as well as sucrose and oil metabolism. Overall, this study offers insights into the genetic mechanisms underlying a high soybean protein content. The identified potential candidate genes can aid marker-assisted selection for developing soybean lines with an increased protein content. [ABSTRACT FROM AUTHOR]

Globally, soybean is a major protein and oil crop. Enhancing our understanding of the soybean domestication and improvement process helps boost genomics-assisted breeding efforts. Here we present a genome-wide variation map of 10.6 million single-nucleotide polymorphisms and 1.4 million indels for 781 soybean individuals which includes 418 domesticated (Glycine max), 345 wild (Glycine soja), and 18 natural hybrid (G. max/G. soja) accessions. We describe the enhanced detection of 183 domestication-selective sweeps and the patterns of putative deleterious mutations during domestication and improvement. This predominantly selfing species shows 7.1% reduction of overall deleterious mutations in domesticated soybean relative to wild soybean and a further 1.4% reduction from landrace to improved accessions. The detected domestication-selective sweeps also show reduced levels of deleterious alleles. Importantly, genotype imputation with this resource increases the mapping resolution of genome-wide association studies for seed protein and oil traits in a soybean diversity panel. The accumulation of recombination events in selfing species may lead to a rapid fixation of both beneficial and deleterious mutations. Here, the authors resequence 781 soybean accessions, show purging of deleterious mutation during domestication, and report genome-wide associations for seed protein and oil traits. [ABSTRACT FROM AUTHOR]

Key message: Genotyping data of a comprehensive Korean soybean collection obtained using a large SNP array were used to clarify global distribution patterns of soybean and address the evolutionary history of soybean. Understanding diversity and evolution of a crop is an essential step to implement a strategy to expand its germplasm base for crop improvement research. Accessions intensively collected from Korea, which is a small but central region in the distribution geography of soybean, were genotyped to provide sufficient data to underpin population genetic questions. After removing natural hybrids and duplicated or redundant accessions, we obtained a non-redundant set comprising 1957 domesticated and 1079 wild accessions to perform population structure analyses. Our analysis demonstrates that while wild soybean germplasm will require additional sampling from diverse indigenous areas to expand the germplasm base, the current domesticated soybean germplasm is saturated in terms of genetic diversity. We then showed that our genome-wide polymorphism map enabled us to detect genetic loci underlying flower color, seed-coat color, and domestication syndrome. A representative soybean set consisting of 194 accessions was divided into one domesticated subpopulation and four wild subpopulations that could be traced back to their geographic collection areas. Population genomics analyses suggested that the monophyletic group of domesticated soybeans was likely originated at a Japanese region. The results were further substantiated by a phylogenetic tree constructed from domestication-associated single nucleotide polymorphisms identified in this study. [ABSTRACT FROM AUTHOR]

Soybean seed protein and oil concentrations are important traits that directly affect the quality of soyfoods. Many studies and breeding programmes have been conducted to find major quantitative trait loci (QTL) that regulate protein and oil concentrations and to develop soybean cultivars with high protein and/or oil content. The purpose of this study was to identify these QTL using a selected breeding population. The population was tested in field conditions over a period of 3 years. Seed protein and oil concentrations were measured each year. Single‐nucleotide polymorphisms (SNPs) were used to construct genetic map using a 180K SoyaSNP array, which identified 1,570 SNPs. We identified 12 QTL for seed protein, 11 for seed oil concentration and four for both traits. Among these, 17 QTL were closely mapped to previously reported QTL, whereas ten sites were novel. Several QTL were detected across at least two experimental years. These loci are good candidate QTL for optimal seed protein and oil concentrations. Our results demonstrate that favourable target QTL can be successfully identified using selected breeding populations. [ABSTRACT FROM AUTHOR]

Pod shattering is an important reproductive process in many wild species. However, pod shattering at the maturing stage can result in severe yield loss. The objectives of this study were to discover quantitative trait loci (QTLs) for pod shattering using two recombinant inbred line (RIL) populations derived from an elite cultivar having pod shattering tolerance, namely "Daewonkong", and to predict novel candidate QTL/genes involved in pod shattering based on their allele patterns. We found several QTLs with more than 10% phenotypic variance explained (PVE) on seven different chromosomes and found a novel candidate QTL on chromosome 16 (qPS-DS16-1) from the allele patterns in the QTL region. Out of the 41 annotated genes in the QTL region, six were found to contain SNP (single-nucleotide polymorphism)/indel variations in the coding sequence of the parents compared to the soybean reference genome. Among the six potential candidate genes, Glyma.16g076600, one of the genes with known function, showed a highly differential expression levels between the tolerant and susceptible parents in the growth stages R3 to R6. Further, Glyma.16g076600 is a homolog of AT4G19230 in Arabidopsis, whose function is related to abscisic acid catabolism. The results provide useful information to understand the genetic mechanism of pod shattering and could be used for improving the efficiency of marker-assisted selection for developing varieties of soybeans tolerant to pod shattering. [ABSTRACT FROM AUTHOR]

Branch number is one of the main factors affecting the yield of soybean (Glycine max (L.)). In this study, we conducted a genome-wide association study combined with linkage analysis for the identification of a candidate gene controlling soybean branching. Five quantitative trait nucleotides (QTNs) were associated with branch numbers in a soybean core collection. Among these QTNs, a linkage disequilibrium (LD) block qtnBR6-1 spanning 20 genes was found to overlap a previously identified major quantitative trait locus qBR6-1. To validate and narrow down qtnBR6-1, we developed a set of near-isogenic lines (NILs) harboring high-branching (HB) and low-branching (LB) alleles of qBR6-1, with 99.96% isogenicity and different branch numbers. A cluster of single nucleotide polymorphisms (SNPs) segregating between NIL-HB and NIL-LB was located within the qtnBR6-1 LD block. Among the five genes showing differential expression between NIL-HB and NIL-LB, BRANCHED1 (BRC1; Glyma.06G210600) was down-regulated in the shoot apex of NIL-HB, and one missense mutation and two SNPs upstream of BRC1 were associated with branch numbers in 59 additional soybean accessions. BRC1 encodes TEOSINTE-BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS 1 and 2 transcription factor and functions as a regulatory repressor of branching. On the basis of these results, we propose BRC1 as a candidate gene for branching in soybean. [ABSTRACT FROM AUTHOR]

Soyasaponin is a type of glycoside such as steroids, steroidal alkaloids or triterpenes, which enhance the body immunity. In order to efficiently identify genes and markers related to the soyasaponin, we used a 180K Axiom® SoyaSNP array and whole genome resequencing data from the Korean soybean core collection. As a result of conducting GWAS for group A soyasaponin (Aa and Ab derivatives), 16 significant common markers associated with Aa and Ab derivatives were mapped to chromosome 7, and three candidate genes including Glyma.07g254600 were detected. The functional haplotypes for candidate genes showed that Aa and Ab contents were mainly determined by alleles of AX-90322128, the marker of Glyma.07g254600. In addition, 14 novel SNPs variants closely associated with Aa and Ab derivatives were discovered for Glyma.07g254600. Therefore, the results of this study that identified soyasaponin-associated markers and useful genes utilizing various genomic information could provide insight into functional soybean breeding. • Group A soyasaponin induces a bitter and astringent taste in soy products, but function to prevent liver damage. • Aa and Ab derivatives of group A soyasaponins were highly associated with genetic factors. • Aa and Ab derivatives of group A soyasaponins were determined by Glyma.07g254600. • Combination of SNP chip with resequencing whole genome enables the identification of markers associated with major traits. [ABSTRACT FROM AUTHOR]