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.

Discovery of new germplasm sources and identification of haplotypes for the durable Soybean mosaic virus resistance gene, Rsv 4, provide novel resources for map-based cloning and genetic improvement efforts in soybean. The Soybean mosaic virus (SMV) resistance locus Rsv4 is of interest because it provides a durable type of resistance in soybean [Glycine max (L.) Merr.]. To better understand its molecular basis, we used a population of 309 BC3F2 individuals to fine-map Rsv4 to a ~120 kb interval and leveraged this genetic information in a second study to identify accessions 'Haman' and 'Ilpumgeomjeong' as new sources of Rsv4. These two accessions along with three other Rsv4 and 14 rsv4 accessions were used to examine the patterns of nucleotide diversity at the Rsv4 region based on high-depth resequencing data. Through a targeted association analysis of these 19 accessions within the ~120 kb interval, a cluster of four intergenic single-nucleotide polymorphisms (SNPs) was found to perfectly associate with SMV resistance. Interestingly, this ~120 kb interval did not contain any genes similar to previously characterized dominant disease resistance genes. Therefore, a haplotype analysis was used to further resolve the association signal to a ~94 kb region, which also resulted in the identification of at least two Rsv4 haplotypes. A haplotype phylogenetic analysis of this region suggests that the Rsv4 locus in G. max is recently introgressed from G. soja. This integrated study provides a strong foundation for efforts focused on the cloning of this durable virus resistance gene and marker-assisted selection of Rsv4-mediated SMV resistance in soybean breeding programs.

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As a predominant plant protein and oil source for both food and feed, soybean is unique in that both domesticated and wild types are predominantly selfing. Here we present a genome-wide variation map of 781 soybean accessions that include 418 domesticated (Glycine max) and 345 wild (Glycine soja) accessions and 18 of their natural hybrids. We identified 10.5 million single nucleotide polymorphisms and 5.7 million small indels that contribute to within-and between-population variations. We describe improved detection of domestication-selective sweeps and drastic reduction of overall deleterious alleles in domesticated soybean relative to wild soybean in contrast to the cost of domestication hypothesis. This resource enables the marker density of existing data sets to be increased to improve the resolution of association studies.

A high-resolution genetic map that was constructed for the Lf1 -residing region will provide valuable information for map-based cloning and genetic improvement efforts in soybean. Changes in leaf architecture as photosynthesis factories remain a major challenge for the improvement of crop productivity. Unlike most soybeans, which have compound leaves comprising three leaflets, the soybean Lf1 mutant has a high frequency of compound leaves with five leaflets in a partially dominant manner. Here, we generated a fine genetic map to determine the genetic basis of this multifoliolate leaf trait. A five-leaflet variant Dusam was found in a recently collected landrace cultivar. Phenotypic data were collected from the F population of a cross between the Dusam and three-leaflet cultivar V94-5152. The mapping results generated using public markers indicated that the five-leaflet determining gene in Dusam is an allele of the previously studied Lf1 gene on chromosome 8. A high-resolution map delimited the genomic region controlling the leaflet number trait to a sequence length of 49 kb. AP2 domain-containing Glyma.08g281900 annotated in this 49 kb region appeared to be a strong candidate for the Lf1-encoding gene, as members of the AP2-type transcription factor family regulate lateral organ development. Dusam additionally exhibits visually distinct phenotypes for shattering and seed-coat cracking traits. However, the two traits were clearly unlinked to the Lf1 gene in our mapping population. Interestingly, the mapping results suggest that the Lf1 gene most likely exerts a pleiotropic effect on the number of seeds per pod. Thus, our results provide a strong foundation towards the cloning of this compound leaf development gene and marker-assisted selection of the seeds per pod trait.