Legume Genomics and Genetics 2024, Vol.15, No.5, 257-269 http://cropscipublisher.com/index.php/lgg 262 promoters of drought-responsive genes provides potential targets for developing synthetic promoters to drive the expression of transgenes under drought conditions (Tripathi et al., 2016). 4.2 Signal transduction pathways Abscisic acid (ABA) is a key hormone involved in the regulation of drought stress responses. ABA-dependent pathways play a significant role in mediating drought tolerance in soybeans. The AREB/ABF transcription factors, including AREB1, AREB2, and ABF3, are master regulators of ABA signaling and are required for the full activation of ABA-responsive genes under drought conditions (Yoshida et al., 2010). These TFs interact with SnRK2 protein kinases, such as SRK2D/SnRK2.2, to regulate the expression of downstream genes involved in drought tolerance. Additionally, the circadian clock components GmLHYs have been shown to negatively control drought tolerance by repressing ABA responses, highlighting the complex interplay between circadian regulation and ABA signaling (Wang et al., 2020). In addition to ABA-dependent pathways, ABA-independent pathways also contribute to drought tolerance in soybeans. The DREB transcription factors, such as GmDREB1 and GmDREB2, play a crucial role in ABA-independent drought responses by binding to DREs in the promoters of stress-responsive genes (Figure 3) (Chen et al., 2007; Kidokoro et al., 2015). These TFs activate the expression of numerous genes involved in various abiotic stress responses, including cold, drought, and high salt, independently of ABA signaling (Kidokoro et al., 2015). Furthermore, the TGA transcription factors, such as GmTGA17, have been shown to enhance drought tolerance through ABA-independent mechanisms, including the regulation of chlorophyll and proline contents and the modulation of ABA-responsive marker genes (Li et al., 2019). 4.3 Genomic and proteomic studies Genomic studies have identified a plethora of drought-responsive genes in soybeans. RNA-seq analysis of drought-tolerant and sensitive soybean genotypes revealed thousands of differentially expressed genes (DEGs) associated with drought stress (Aleem et al., 2020). These DEGs are involved in various biological processes, including water and auxin transport, cell wall/membrane integrity, antioxidant activity, and secondary metabolism (Aleem et al., 2020). Notably, several DEGs were located in QTL-rich regions associated with drought stress, and some exhibited non-synonymous SNP polymorphisms, making them potential candidates for further functional validation. Proteomic studies have provided insights into the proteins involved in drought tolerance in soybeans. For instance, the identification of stress-responsive proteins, such as those involved in ABA and Ca2 + signaling, has highlighted their role in enhancing drought tolerance (Wei et al., 2019). Additionally, the proteomic profiling of drought-stressed soybean roots and leaves identified significant changes in the levels of metabolites and proteins, including a 160-fold increase in the coumestan coumestrol, which may serve as a biomarker for drought and a target for improving drought responses (Tripathi et al., 2016). These studies underscore the importance of integrating genomic and proteomic approaches to unravel the complex molecular mechanisms underlying drought tolerance in soybeans. In summary, the molecular bases of drought tolerance in soybeans involve a complex network of gene expression and regulation, signal transduction pathways, and genomic and proteomic changes. Understanding these mechanisms provides valuable insights for developing strategies to enhance drought tolerance in soybeans and other crops. 5 Integrative Approaches to Drought Tolerance 5.1 Systems biology approaches Systems biology approaches have been instrumental in understanding the complex mechanisms underlying drought tolerance in soybeans. By integrating transcriptomics, proteomics, and metabolomics, researchers have identified key genes, proteins, and metabolites involved in drought response. For instance, comprehensive RNA-seq analysis has revealed differentially expressed genes (DEGs) associated with water and auxin transport,
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