Overexpression of the Wild Soybean Expansin Gene GsEXPB1 Enhances Salt Stress Tolerance in Transgenic Soybeans

As the ancestor and close relative of soybeans, wild soybeans exhibit strong salt tolerance and are ideal materials for discovering salt-tolerant genes. Expansins are a type of cell wall-loosening protein that plays an active role in regulating plant salt tolerance. We previously obtained the wild soybean expansin gene <i>GsEXPB1</i>, which is specifically transcribed in roots and actively responds to salt stress. Overexpression of this gene significantly promotes the growth of soybean hairy roots under salt stress. To further elucidate the function of the gene in regulating plant tolerance to salt stress, this study obtained soybean hairy roots that overexpress the <i>GsEXPB1</i> gene and silence its homologous gene <i>GmEXPB4</i> through RNAi. Under salt stress, the overexpression of the <i>GsEXPB1</i> gene significantly promoted the growth of soybean hairy roots, while the hairy roots that were silenced for the <i>GmEXPB4</i> gene exhibited an opposite phenotype. Physiological assay results indicate that <i>GsEXPB1</i> enhances the tolerance of soybean hairy roots to salt stress by regulating the antioxidant system and Na⁺/K⁺ content. In soybean lines overexpressing <i>GsEXPB1</i>, the germination rate of seeds and root growth indicators under salt stress were significantly improved compared to those of wild-type plants. Meanwhile, <i>GsEXPB1</i> enhances the tolerance of transgenic lines to salt stress by actively regulating the antioxidant system, osmotic adjustment system, chlorophyll content, cell wall components, and Na⁺/K⁺ levels, significantly promoting growth and increasing the number of flowers and grain weight. This study reveals the physiological mechanism by which <i>GsEXPB1</i> enhances soybean salt tolerance, providing a theoretical basis and relevant references for the application of this gene in the breeding of new soybean salt-tolerant varieties.