Background: Cultivated soybean (Glycine max) is a major agricultural crop that provides a crucial source of edible protein and oil. Decreased amounts of saturated palmitic acid and increased amounts of unsaturated oleic acid in soybean oil are considered optimal for human cardiovascular health and therefore there has considerable interest by breeders in discovering genes affecting the relative concentrations of these fatty acids. Using a genome-wide association (GWA) approach with nearly 30,000 single nucleotide polymorphisms (SNPs), we investigated the genetic basis of protein, oil and all five fatty acid levels in seeds from a sample of 570 wild soybeans (Glycine soja), the progenitor of domesticated soybean, to identify quantitative trait loci (QTLs) affecting these seed composition traits.Results: We discovered 29 SNPs located on ten different chromosomes that are significantly associated with the seven seed composition traits in our wild soybean sample. Eight SNPs co-localized with QTLs previously uncovered in linkage or association mapping studies conducted with cultivated soybean samples, while the remaining SNPs appeared to be in novel locations. Twenty-four of the SNPs significantly associated with fatty acid variation, with the majority located on chromosomes 14 (6 SNPs) and seven (8 SNPs). Two SNPs were common for two or more fatty acids, suggesting loci with pleiotropic effects. We also identified some candidate genes that are involved in fatty acid metabolism and regulation. For each of the seven traits, most of the SNPs produced differences between the average phenotypic values of the two homozygotes of about one-half standard deviation and contributed over 3% of their total variability.Conclusions: This is the first GWA study conducted on seed composition traits solely in wild soybean populations, and a number of QTLs were found that have not been previously discovered. Some of these may be useful to breeders who select for increased protein/oil content or altered fatty acid ratios in the seeds. The results also provide additional insight into the genetic architecture of these traits in a large sample of wild soybean, and suggest some new candidate genes whose molecular effects on these traits need to be further studied.

Amino acids play vital roles in the central metabolism of seeds. They are primarily utilized for the synthesis of seed-storage proteins, but also serve as precursors for the biosynthesis of secondary metabolites and as a source of energy. Here, we aimed at describing the knowledge accumulated in recent years describing the changes occurring in the contents of free amino acids (FAAs) during seed development. Since several essential amino acids are found in low levels in seeds (e.g., Lys, Met, Thr, Val, Leu, Ile and His), or play unique functional roles in seed development (e.g., Pro and the non-proteinogenic γ-aminobutyrate [GABA]), we also briefly describe studies carried out in order to alter their levels in seeds and determine the effects of the manipulation on seed biology. The lion share of these studies highlights strong positive correlations between the biosynthetic pathways of FAAs, meaning that when the levels of a certain amino acid change in seeds, the contents of other FAAs tend to elevate as well. These observations infer a tight regulatory network operating in the biosynthesis of FAAs during seed development.Copyright © 2018 Elsevier B.V. All rights reserved.

Wild soybean (Glycine soja) is a valuable genetic resource for soybean improvement. Seed composition profiles provide beneficial information for the effective conservation and utilization of wild soybeans. Therefore, this study aimed to assess the variation in free amino acid abundance in the seeds of wild soybean germplasm collected in Japan. The free amino acid content in the seeds from 316 accessions of wild soybean ranged from 0.965 to 5.987 mg/g seed dry weight (DW), representing a 6.2-fold difference. Three amino acids had the highest coefficient of variation (CV): asparagine (1.15), histidine (0.95) and glutamine (0.94). Arginine (0.775 mg/g DW) was the predominant amino acid in wild soybean seeds, whereas the least abundant seed amino acid was glutamine (0.008 mg/g DW). A correlation network revealed significant positive relationships among most amino acids. Wild soybean seeds from different regions of origin had significantly different levels of several amino acids. In addition, a significant correlation between latitude and longitude of the collection sites and the total free amino acid content of seeds was observed. Our study reports diverse phenotypic data on the free amino acid content in seeds of wild soybean resources collected from throughout Japan. This information will be useful in conservation programmes for Japanese wild soybean and for the selection of accessions with favourable characteristics in future legume crop improvement efforts.

Seed composition, including the protein, lipid and sucrose contents of 334 accessions of wild soybean (Glycine soja) collected in Japan, was evaluated using near-infrared reflectance spectroscopy (NIRS) technology. The distribution of protein, lipid and sucrose contents and correlations among these three classes of seed components were determined. Protein, lipid and sucrose levels ranged in accessions from 48.6 to 57.0, 9.0 to 14.3 and 1.24 to 3.53%, respectively. Average levels of protein, lipid and sucrose in the accessions were 54, 11 and 2.5%, respectively. High negative correlations were observed between the protein and lipid contents, and the protein and sucrose contents. Mean levels of the three constituents were compared among collection sites classified by climatic conditions. The total protein content of accessions from regions with a high annual mean temperature was high. The protein content of accessions from the II-1 region was higher than those from the III-3 region, and the sucrose content from the II-1 region was lower than those from regions III-2 and IV-3. The lipid content of plants from the II-1 region was lower than those from other regions, and the accessions in region II had a higher protein content and lower sucrose and lipid contents than the other regions. These results provide diverse and wide-ranged protein, lipid and sucrose contents information of Japanese wild soybean resources according to climatic region; thus, providing a foundation for the future development and selection of new soybean varieties with desired traits in global environmental changes.

Soybean [Glycine max (L.) Merr.] produces a high‐quality protein that provides an appropriate balance of amino acids for monogastric animals. It has been reported that the relative abundance of some essential amino acids may be reduced in soybean with high protein concentration. A dilution of essential amino acids in soybean protein would lead to a reduction in the value of that protein to the end user, and undefined variation in amino acid balance of soybean would lead to poorly balanced animal rations. The objective of this work was to determine whether amino acid balance is affected by seed protein concentration and to characterize any putative changes in the relative abundance of each amino acid across a range of soybean protein concentrations. We created a wide range of protein concentrations in soybean seed by imposing managed stress treatments previously shown to lower or raise protein concentration. We found that the amino acid composition of soybean protein was affected by protein concentration. The relative abundance of amino acids that are often limiting for animal growth, such as lysine, methionine, cysteine, tryptophan, and threonine, were reduced with increasing seed protein concentrations, whereas arginine and glutamic acid were increased. However, treatments used in this study uncovered a potential role for the availability and source of reduced C and N to impact the relative abundance of each amino acid independently, highlighting the complexity of this interrelationship.

Amino acids are essential for proper growth and development in plants. Amino acids serve as building blocks for proteins but also are important for responses to stress and the biosynthesis of numerous essential compounds. In seed, the pool of free amino acids (FAAs) also contributes to alternative energy, desiccation, and seed vigor; thus, manipulating FAA levels can significantly impact a seed's nutritional qualities. While genome-wide association studies (GWAS) on branched-chain amino acids have identified some regulatory genes controlling seed FAAs, the genetic regulation of FAA levels, composition, and homeostasis in seeds remains mostly unresolved. Hence, we performed GWAS on 18 FAAs from a 313-ecotype Arabidopsis (Arabidopsis thaliana) association panel. Specifically, GWAS was performed on 98 traits derived from known amino acid metabolic pathways (approach 1) and then on 92 traits generated from an unbiased correlation-based metabolic network analysis (approach 2), and the results were compared. The latter approach facilitated the discovery of additional novel metabolic interactions and single-nucleotide polymorphism-trait associations not identified by the former approach. The most prominent network-guided GWAS signal was for a histidine (His)-related trait in a region containing two genes: a cationic amino acid transporter (CAT4) and a polynucleotide phosphorylase resistant to inhibition with fosmidomycin. A reverse genetics approach confirmed CAT4 to be responsible for the natural variation of His-related traits across the association panel. Given that His is a semiessential amino acid and a potent metal chelator, CAT4 orthologs could be considered as candidate genes for seed quality biofortification in crop plants.© 2017 American Society of Plant Biologists. All Rights Reserved.

The mitochondrial glycine decarboxylase multienzyme system, connected to serine hydroxymethyltransferase through a soluble pool of tetrahydrofolate, consists of four different component enzymes, the P-, H-, T- and L-proteins. In a multi-step reaction, it catalyses the rapid destruction of glycine molecules flooding out of the peroxisomes during the course of photorespiration. In green leaves, this multienzyme system is present at tremendously high concentrations within the mitochondrial matrix. The structure, mechanism and biogenesis of glycine decarboxylase are discussed. In the catalytic cycle of glycine decarboxylase, emphasis is given to the lipoate-dependent H-protein that plays a pivotal role, acting as a mobile substrate that commutes successively between the other three proteins. Plant mitochondria possess all the necessary enzymatic equipment for de novo synthesis of tetrahydrofolate and lipoic acid, serving as cofactors for glycine decarboxylase and serine hydroxymethyltransferase functioning.

The aromatic amino acids phenylalanine, tyrosine, and tryptophan in plants are not only essential components of protein synthesis, but also serve as precursors for a wide range of secondary metabolites that are important for plant growth as well as for human nutrition and health. The aromatic amino acids are synthesized via the shikimate pathway followed by the branched aromatic amino acids biosynthesis pathway, with chorismate serving as a major intermediate branch point metabolite. Yet, the regulation and coordination of synthesis of these amino acids are still far from being understood. Recent studies on these pathways identified a number of alternative cross-regulated biosynthesis routes with unique evolutionary origins. Although the major route of Phe and Tyr biosynthesis in plants occurs via the intermediate metabolite arogenate, recent studies suggest that plants can also synthesize phenylalanine via the intermediate metabolite phenylpyruvate (PPY), similarly to many microorganisms. Recent studies also identified a number of transcription factors regulating the expression of genes encoding enzymes of the shikimate and aromatic amino acids pathways as well as of multiple secondary metabolites derived from them in Arabidopsis and in other plant species.

The relatively low genetic variation of current US soybean [Glycine max (L.) Merr.] cultivars constrains the improvement of grain yield and other agronomic and seed composition traits. Recently, a substantial effort has been undertaken to introduce novel genetic diversity present in wild soybean (Glycine soja Siebold & Zucc.) into elite cultivars, in both public and private breeding programs. The objectives of this research were to evaluate the phenotypic diversity within a collection of 80 G. soja plant introductions (PIs) in the USDA National Genetic Resources Program and to analyze the correlations between agronomic and seed composition traits. Field tests were conducted in Missouri and North Carolina during 3 yr (2013, 2014, and 2015) in a randomized complete block design. The phenotypic data collected included plant maturity date, seed weight, and the seed concentration of protein, oil, essential amino acids, fatty acid, and soluble carbohydrates. We found that genotype was a significant (P < 0.0001) source of variation for maturity date, seed weight, seed protein and amino acids, seed oil and fatty acids, and seed carbohydrates, and significant correlations were observed between numerous traits. The G. soja PIs generally had lower seed weight, higher seed contents of protein, linolenic acid, raffinose, and stachyose, and lower seed contents of oil and oleic acid than the cultivated soybean G. max lines. The information and data collected in this study will be invaluable in guiding soybean breeders and geneticists in selecting promising G. soja PIs for research and cultivar improvement.

A fundamental goal in evolutionary biology is to understand how various evolutionary factors interact to affect the population structure of diverse species, especially those of ecological and/or agricultural importance such as wild soybean (Glycine soja). G. soja, from which domesticated soybeans (Glycine max) were derived, is widely distributed throughout diverse habitats in East Asia (Russia, Japan, Korea, and China). Here, we utilize over 39,000 single nucleotide polymorphisms genotyped in 99 ecotypes of wild soybean sampled across their native geographic range in northeast Asia, to understand population structure and the relative contribution of environment versus geography to population differentiation in this species. A STRUCTURE analysis identified four genetic groups that largely corresponded to the geographic regions of central China, northern China, Korea, and Japan, with high levels of admixture between genetic groups. A canonical correlation and redundancy analysis showed that environmental factors contributed 23.6% to population differentiation, much more than that for geographic factors (6.6%). Precipitation variables largely explained divergence of the groups along longitudinal axes, whereas temperature variables contributed more to latitudinal divergence. This study provides a foundation for further understanding of the genetic basis of climatic adaptation in this ecologically and agriculturally important species.