The soybean gene GmSP1L-8 improves salt tolerance through the enhancement of the ROS scavenging system.

Microtubule-associated proteins (MAPs) are key regulators of plant stress responses. Although salt stress-induced microtubule dynamics have been widely observed, how specific microtubule-associated factors coordinately regulate plant salt tolerance remains to be further elucidated. In this study, through genome-wide identification and expression profiling of the GmSP1L gene family in soybean (Glycine max), we screened and identified GmSP1L-8, a protein that is significantly induced by salt stress. Subcellular localization analysis revealed that GmSP1L-8 localizes to both the nucleus and cytoplasm; notably, it displays a distinct filamentous pattern within the cytoplasm, characteristic of cytoskeletal-associated proteins. Functional validation demonstrated that GmSP1L-8 confers salt tolerance in Saccharomyces cerevisiae and in soybean plants harboring GmSP1L-8 overexpressing hairy roots. Physiological analysis revealed that the overexpression lines maintained lower reactive oxygen species (ROS) levels, with significantly reduced relative electrical conductivity and malondialdehyde (MDA) content, effectively preserving cell membrane integrity and alleviating membrane lipid peroxidation. For mechanistic investigation, a soybean yeast two-hybrid library was constructed and screened, identifying GmHMGR4, a key rate-limiting enzyme in the mevalonate (MVA) pathway, as a direct interacting partner of GmSP1L-8. The physical association between the two proteins was further confirmed by point-to-point Y2H, bimolecular fluorescence complementation (BiFC), and molecular docking simulations. In vitro biochemical assays demonstrated that GmSP1L-8 significantly enhanced the enzymatic activity of GmHMGR4 in a dose-dependent manner, thereby activating the downstream ROS scavenging system. Additionally, experimental observations revealed that GmSP1L-8 displayed a pronounced filamentous pattern resembling microtubule bundling under salt stress, suggesting that it may participate in regulation through the dual pathways of maintaining microtubule cytoskeleton stability and enhancing metabolic enzyme activity. In conclusion, this study reveals a novel GmSP1L-8-mediated salt tolerance mechanism in soybean, providing a new perspective for understanding the potential synergy between the cytoskeleton and metabolic adaptation, and offers an important candidate target for molecular breeding of stress resistance in soybean.