Sybeans have been grown by plant breeding for decades. As soybeans have very limited genetic variation, it is difficult for soybean breeders to find new genetic resources for abiotic stressors. Recently, soybeans have been exposed to flooding stress from intensive summer rainfall owing to climate change. Glycine soja, a wild soybean, is known to have greater genetic variation and greater resistance to a variety of biotic and abiotic stresses than ordinary soybeans. In this study, high-throughput transcriptome analysis was performed using flood-treated Glycine soja. Differentially expressed genes (DEGs) were analyzed using reads mapped to reference sequences, and gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed using selected DEGs. In addition, RT-qPCR analysis was performed to further analyze the expression of specific candidate genes. Several novel genes that could explain various mechanisms related to water stress were identified as related transcripts and adaptation mechanisms through cell wall expansion, alcoholic fermentation under anaerobic conditions, and structural changes. In addition, most of the isoflavonoid daidzein pathway genes exhibited upregulated expression under flooding stress. Interestingly, expression of the DIR (dirigent protein 1-like) gene, which is known to decrease in response to flooding stress in soybeans (Glycine max), was upregulated in Glycine soja. The expression of DIR revealed that DIR may play a key role in conferring flooding stress resistance in Glycine soja. This study provides useful information regarding the genes and comprehensive adaptation mechanisms related to flooding stress tolerance that can be utilized for cultivated soybeans through the Korean wild soybean.

Flooding stress causes a significant reduction in soybean yield. The development of flood-tolerant cultivars is an effective way to minimize yield loss due to flooding. Information on candidate genes for flooding tolerance is useful for developing tolerant lines. The
objective
of this study was to identify potential candidate genes for flooding tolerance in soybean by integrating the results of a quantitative trait locus analysis and RNA sequencing. A total of 19 genes showed good amplification in capillary electrophoresis and were further analyzed through a reverse transcription quantitative polymerase chain reaction (qRT-PCR); two of these genes showed differential expression among tolerant and susceptible lines. The expression of Glyma.12g030900 and Glyma.10g050300 in leaf and root tissues, respectively, was higher in several tolerant lines than in the susceptible lines under flooding stress. The chlorophyll index of the tolerant lines was also consistently higher than that of the susceptible lines over two years, supporting the qRT-PCR results. This study provides useful information on flooding tolerance in soybeans.

Soybean [Glycine max. (L.) Merr] is one of the most important legumes in the world. However, soybean varieties are sensitive to flooding stress and their seed yields are substantially reduced in response to the flooding stress. 192 soybean germplasm collection was screened to identify flooding tolerant germplasm at an early vegetative growth stage (V1). Soybean plants at V1 stage were waterlogged for 4 to 10 days. To evaluate flooding tolerance, survival rate were investigated as a time dependent manner. Jangbaegkong, Danbaegkong, Sowonkongkong, Socheong2 and Suwon269 showed flooding tolerance, while Shillog, T201, T181, NTS1116 and HP-963 showed flooding sensitivity. We also investigated effects of flooding stress on soybean morphology. The adventitious root development was greatly increased in flooding tolerant plants compared to it in flooding sensitive plants. In addition, root length and root number were analyzed. The significant reduction of root length and root number was observed in flooding sensitive plants. Thus, these results indicate that the morphological changes in roots are important for acclimation to flooding stress. Taken together, the relationship between the morphological changes in the roots and flooding tolerance may be useful in selecting a flooding tolerant soybean germplasm.