Metabolomic understanding of pod removal effect in soybean plants and potential association with their health benefit.

Since natural materials, such as phytochemicals in plants, are increasingly being used for foods and skincare due to their beneficial functions, it is important for developing the cultivation practices to increase the contents of phytochemicals. We here explored metabolite perturbations in the leaves of soybean plants when their pods were removed during growth through 1H NMR-based metabolomics approach. There were obvious metabolic differences in the leaves between normal and pod-removed soybean plants. High amounts of primary metabolites in pod-removed soybean leaves, including amino acids, sugars, and fatty acids, reflected a delay of leaf senescence caused by pod removal. In particular, amounts of isoflavones, coumestrol, and apigenin derivatives in pod-removed soybean leaves were substantially increased. These were considered as distinct metabolic influences of pod removal in soybean plants. These results indicate that pod removal of soybean plants can induce significant perturbations of various metabolites in their soybean leaves, providing useful information to improve the quality of soybean leaves by increasing amounts of bioactive components.

Metabotyping of different soybean genotypes and distinct metabolism in their seeds and leaves.

The metabolome of three soybean genotypes, Glycine max Hwangkeum (elite or domesticated cultivar), Glycine max Napjakong (landrace or semi-wild cultivar) and Glycine soja Dolkong (wild cultivar), were characterized in seeds and leaves using a 1H NMR-based metabolomics approach. Expression of primary and secondary metabolites were different in seeds and leaves as well as amongst soybean genotypes. Different kaempferol glycosides were observed in the leaves but not in the seeds, and quercetin derivatives were found only in G. max Napjakong and G. soja Dolkong. Moreover, epicatechin was found only in the seeds of G. max Napjakong and G. soja Dolkong. These results demonstrate distinct adaptations of different soybean genotypes to given environmental conditions. The current study, therefore, provides useful information on global metabolic compositions that might be used to develop soybean-based products through better understanding of the metabolic phenotypes of existing soybean genotypes.

Comprehensive RNA sequencing and co-expression network analysis to complete the biosynthetic pathway of coumestrol, a phytoestrogen.

Coumestrol (CMS), a coumestan isoflavone, plays key roles in nodulation through communication with rhizobia, and has been used as phytoestrogens for hormone replacement therapy in humans. Because CMS content is controlled by multiple genetic factors, the genetic basis of CMS biosynthesis has remained unclear. We identified soybean genotypes with consistently high (Daewonkong) or low (SS0903-2B-21-1-2) CMS content over 2 years. We performed RNA sequencing of leaf samples from both genotypes at developmental stage R7, when CMS levels are highest. Within the phenylpropanoid biosynthetic pathway, 41 genes were tightly connected in a functional co-expression gene network; seven of these genes were differentially expressed between two genotypes. We identified 14 candidate genes involved in CMS biosynthesis. Among them, seven were annotated as encoding oxidoreductases that may catalyze the transfer of electrons from daidzein, a precursor of CMS. Two of the other genes, annotated as encoding a MYB domain protein and a MLP-like protein, may increase CMS accumulation in response to stress conditions. Our results will help to complete our understanding of the CMS biosynthetic pathway, and should facilitate development of soybean cultivars with high CMS content that could be used to promote the fitness of plants and human beings.

Metabolomics approach for understanding geographical dependence of soybean leaf metabolome.

The soybean plant (Glycine max) is widely used as an ingredient in various foods, nutraceuticals and cosmetics, due to their diverse bioactive compounds. Their metabolic compositions are likely affected by environmental conditions during growth. To investigate the influence of different environmental conditions on the metabolite composition of soybean leaves, we cultivated soybean (G. max Sinhwa) in the southernmost island and volcanic region of Korea, and in the central section and limestone region of the Korean peninsula. Comprehensive metabolite variations of their leaves were analyzed through 1H NMR-based metabolomics approach. With marked differences in soil compositions and climatic conditions between the two growing areas, differences in accumulations of pinitol and diverse flavonoids were noted between the soybean leaves, reflecting the distinct metabolism of soybean plants for physiological adaptation toward different environmental conditions. Therefore, the current study highlights the geographical dependences of diverse soybean leaf metabolites for developing biofunction-enhanced soybean products.

Transcriptomic variation in proanthocyanidin biosynthesis pathway genes in soybean (Glycine spp.).

BACKGROUND: Proanthocyanidins are oligomeric or polymeric end products of flavonoid metabolic pathways starting with the central phenylpropanoid pathway. Although soybean (Glycine spp.) seeds represent a major source of nutrients for the human diet, as well as components for the cosmetics industry as a result of their high levels of flavonoid metabolites, including isoflavonoids, anthocyanins and proanthocyanidins, the genetic regulatory mechanisms underlying proanthocyanidin biosynthesis in soybean remain unclear. RESULTS: We evaluated interspecific and intraspecific variability in flavonoid components in soybean using 43 cultivars, landraces and wild soybean accessions. We performed transcriptomic profiling of genes encoding enzymes involved in flavonoid biosynthesis using three soybean genotypes, Hwangkeum (elite cultivar), IT109098 (landrace) and IT182932 (wild accession), in seeds. We identified a Glycine max landrace, IT109098, with a proanthocyanidin content as high as that of wild soybean. Different homologous genes for anthocyanidin reductase, which is involved in proanthocyanidin biosynthesis, were detected as differentially expressed genes between IT109098 and IT182932 compared to Hwangkeum. CONCLUSION: We detected major differences in the transcriptional levels of genes involved in the biosynthesis of proanthocyanidin and anthocyanin among genotypes beginning at the early stage of seed development. The results of the present study provide insights into the underlying genetic variation in proanthocyanidin biosynthesis among soybean genotypes. © 2017 Society of Chemical Industry.

Distinctive Metabolism of Flavonoid between Cultivated and Semiwild Soybean Unveiled through Metabolomics Approach.

Soybeans are an important crop for agriculture and food, resulting in an increase in the range of its application. Recently, soybean leaves have been used not only for food products but also in the beauty industry. To provide useful and global metabolite information on the development of soy-based products, we investigated the metabolic evolution and cultivar-dependent metabolite variation in the leaves of cultivated (Glycine max) and semiwild (G. gracilis) soybean, through a (1)H NMR-based metabolomics approach, as they grew from V (vegetative) 1 to R (reproductive) 7 growth stages. The levels of primary metabolites, such as sucrose, amino acids, organic acids, and fatty acids, were decreased both in the G. gracilis and G. max leaves. However, the secondary metabolites, such as pinitol, rutin, and polyphenols, were increased while synthesis of glucose was elevated as the leaves grew. When metabolite variations between G. gracilis and G. max are compared, it was noteworthy that rutin and its precursor, quercetin-3-O-glucoside, were found only in G. gracilis but not in G. max. Furthermore, levels of pinitol, proline, ß-alanine, and acetic acid, a metabolite related to adaptation toward environmental stress, were different between the two soybean cultivars. These results highlight their distinct metabolism for adaptation to environmental conditions and their intrinsic metabolic phenotype. This study therefore provides important information on the cultivar-dependent metabolites of soybean leaves for better understanding of plant physiology toward the development of soy-based products.