Legume Genomics and Genetics 2026, Vol.17, No.1, 32-48 http://cropscipublisher.com/index.php/lgg 35 Comparative studies among cultivated and wild soybean germplasm show that drought-tolerant lines generally sustain better photosynthetic performance, less MDA accumulation, and more effective antioxidant and osmotic regulation than sensitive counterparts, underscoring the strong link between physiological plasticity and drought tolerance (Xu et al., 2023; Lin et al., 2024). 2.2 Plant drought resistance signal transduction pathways The perception and transduction of drought signals in soybean rely on complex networks integrating cellular sensors, secondary messengers, and phytohormones. Water deficit is first perceived as changes in cell turgor and osmotic potential, leading to rapid calcium (Ca2+) influx, ROS bursts, and alterations in membrane lipid-derived messengers such as phosphatidic acid (Soma et al., 2021). These early signals activate protein kinase cascades, including Ca2+-dependent protein kinases and mitogen-activated protein kinase (MAPK) modules, which phosphorylate downstream targets to reprogram metabolism, ion fluxes, and gene expression (Soma et al., 2021; Li et al., 2022). In drought-tolerant soybean cultivars, transcriptome analyses have revealed preferential induction of signal transduction pathways such as Ca2+ signaling, MAPK signaling, and lipid signaling (e.g., phosphatidylinositol 4-phosphate 5-kinase), suggesting that more robust and diversified signaling underlies enhanced stress perception and response (Xu et al., 2023). Abscisic acid (ABA) is the central hormonal regulator of drought resistance. Under water deficit, ABA accumulates in leaves and roots and binds to PYR/PYL/RCAR receptors, leading to inhibition of PP2C phosphatases and activation of subclass III SnRK2 kinases (Soma et al., 2021). Activated SnRK2s phosphorylate ion channels in guard cells to promote stomatal closure, as well as downstream transcription factors such as ABA-responsive element binding proteins/factors (AREB/ABFs), thereby coupling rapid physiological responses with transcriptional reprogramming. ABA-independent pathways function in parallel, involving subclass I SnRK2s, which modulate gene expression stability via mRNA decay and growth regulation during drought. Crosstalk between ABA and other hormones-including jasmonic acid, brassinosteroids, and ethylene-further shapes the drought response, with comparative transcriptomics in soybean showing that jasmonate- and brassinosteroid-related signaling components are particularly enriched in drought-tolerant genotypes (Xu et al., 2023). Recent work in soybean has also uncovered a circadian-linked module in which GmPRR3b modulates ABA signaling and drought responses via repression of the ABA-responsive transcription factor GmABF3, illustrating how core clock components integrate environmental water signals with temporal regulation of stress defenses (Li et al., 2024). 2.3 Regulatory mechanisms of drought stress-related gene expression Drought-induced transcriptional reprogramming in soybean is governed by multilayered regulatory networks centered on transcription factors (TFs) that act as molecular switches. ABA-dependent regulation largely proceeds through ABRE-binding bZIP TFs (AREB/ABFs), which bind ABA-responsive elements (ABREs) in target promoters to activate genes involved in osmotic adjustment, LEA proteins, and antioxidant systems (Soma et al., 2021; Wei et al., 2024). ABA-independent regulation involves dehydration-responsive element (DRE)-binding proteins (DREB/CBF) and the broader AP2/ERF family, as well as NAC, MYB, bHLH, and WRKY TFs, which interact with DRE and other cis-elements to control suites of drought-responsive genes (Soma et al., 2021; Wei et al., 2024). Integrative systems analyses of soybean transcriptomes have identified co-expression modules enriched for these TF families, with hub genes predicted to coordinate pathways such as photosynthesis, redox homeostasis, and systemic acquired resistance under water deficit (Shahriari et al., 2022). Comparative RNA-seq studies consistently report that drought-tolerant soybean genotypes exhibit a greater number and magnitude of differentially expressed TF genes than sensitive lines, particularly in NAC, WRKY, bZIP, ERF, and NF-Y families, indicating stronger or earlier transcriptional activation of protective pathways (Shahriari et al., 2022; Xu et al., 2023; Wei et al., 2024). Functional characterization of individual TFs has begun to clarify how these regulators confer drought tolerance. Overexpression of NAC-type TFs such as GmNAC19 and GmNAC3 enhances drought resistance by improving root development, maintaining chlorophyll content, and modulating key physiological indices, including soluble
RkJQdWJsaXNoZXIy MjQ4ODYzNA==