Drought is a major abiotic stressor that causes yield losses and limits the growing area for most crops. Soybeans are an important legume crop that is sensitive to water-deficit conditions and suffers heavy yield losses from drought stress. To improve drought-tolerant soybean cultivars through breeding, it is necessary to understand the mechanisms of drought tolerance in soybeans. In this study, we applied several transcriptome datasets obtained from soybean plants under drought stress in comparison to those grown under normal conditions to identify novel drought-responsive genes and their underlying molecular mechanisms. We found 2168 significant up/downregulated differentially expressed genes (DEGs) and 8 core modules using gene co-expression analysis to predict their biological roles in drought tolerance. Gene Ontology and KEGG analyses revealed key biological processes and metabolic pathways involved in drought tolerance, such as photosynthesis, glyceraldehyde-3-phosphate dehydrogenase and cytokinin dehydrogenase activity, and regulation of systemic acquired resistance. Genome-wide analysis of plants’ cis-acting regulatory elements (CREs) and transcription factors (TFs) was performed for all of the identified DEG promoters in soybeans. Furthermore, the PPI network analysis revealed significant hub genes and the main transcription factors regulating the expression of drought-responsive genes in each module. Among the four modules associated with responses to drought stress, the results indicated that GLYMA_04G209700, GLYMA_02G204700, GLYMA_06G030500, GLYMA_01G215400, and GLYMA_09G225400 have high degrees of interconnection and, thus, could be considered as potential candidates for improving drought tolerance in soybeans. Taken together, these findings could lead to a better understanding of the mechanisms underlying drought responses in soybeans, which may useful for engineering drought tolerance in plants.

Biotic stresses are environmental factors that cause a variety of crop diseases and damages. In contrast, crops trigger specific transduction signaling pathways that the hormones are the central players. Integrative OMICS for systems genetic engineering approach contributes in the understanding of molecular mechanisms. In this research, the system biology approaches were applied to discover particular molecular interactions between biotic stresses and hormonal signaling in barley. The meta-analysis of the data identified a total of 1232 and 304 differentially expressed genes (DEGs) respectively so that were significantly involved in defense processes and hormone signaling. A total of 24 TFs belonged to 15 conserved families and 6 TFs belonged to 6 conserved families were identified for biotic and hormonal data respectively, whereas NF-YC, GNAT, and whirly families were the most abundant groups. The functional analysis of the upstream regions for over-represented cis-acting elements revealed that were involved activation of transcription factors in response to pathogens and hormones. Based on the co-expression analysis, 6 and 7 distinct co-expression modules related to biotic stresses and hormonal signaling were respectively uncovered. The gene network analysis also identified novel hub genes such as TIM10, DRT101, ADG1, and TRA2 which may be involved in regulating defense responses to biotic stresses. In addition, many new genes with unknown function were obtained. Since this study represents a first preliminary curated system biology analysis of barley transcriptomic responses to biotic stresses and hormone treatments, introduces important candidate genes that may be beneficial to crop biotechnologists to accelerate genetic engineering programs.

Biotic stresses are pests and pathogens that cause a variety of crop diseases and damages. In response to these agents, crops trigger specific defense signal transduction pathways in which hormones play a central role. To recognize hormonal signaling, we integrated barley transcriptome datasets related to hormonal treatments and biotic stresses. In the meta-analysis of each dataset, 308 hormonal and 1232 biotic DEGs were identified respectively. According to the results, 24 biotic TFs belonging to 15 conserved families and 6 hormonal TFs belonging to 6 conserved families were identified, with the NF-YC, GNAT, and WHIRLY families being the most prevalent. Additionally, gene enrichment and pathway analyses revealed that over-represented cis-acting elements were recognized in response to pathogens and hormones. Based on the co-expression analysis, 6 biotic and 7 hormonal modules were uncovered. Finally, the hub genes of PKT3, PR1, SSI2, LOX2, OPR3, and AOS were candidates for further study in JA- or SA-mediated plant defense. The qPCR confirmed that the expression of these genes was induced from 3 to 6 h following exposure to 100 μM MeJA, with peak expression occurring between 12 h and 24 h and decreasing after 48 h. Overexpression of PR1 was one of the first steps toward SAR. As well as regulating SAR, NPR1 has also been shown to be involved in the activation of ISR by the SSI2. LOX2 catalyzes the first step of JA biosynthesis, PKT3 plays an important role in wound-activated responses, and OPR3 and AOS are involved in JA biosynthesis. In addition, many unknown genes were introduced that can be used by crop biotechnologists to accelerate barley genetic engineering.