<scp>ScHAL1</scp> ‐Mediated Enhancement of Salt Tolerance in Soybean: From Stable Transgenic Inheritance to Field Trial Validation

To develop salt-tolerant transgenic soybeans, ScHAL1 from Saccharomyces cerevisiae (yeast), which increases salt tolerance by maintaining high intracellular K⁺ concentrations and decreasing intracellular Na⁺ during salt stress, was introduced into soybean (Glycine max L. Merr.) through Agrobacterium tumefaciens-mediated transformation. Among the 373 transgenic plants generated, three lines (TL1, TL2 and TL3) exhibiting stable and enhanced salt tolerance via ScHAL1-mediated ion homeostasis were selected. Molecular analyses of the transgenic lines by polymerase chain reaction (PCR), Southern blotting, reverse transcription-PCR (RT-PCR), quantitative reverse-transcription polymerase chain reaction (qRT-PCR), western blotting and enzyme-linked immunosorbent assay (ELISA) showed that ScHAL1 and bar transgenes were stably inherited and expressed across multiple generations (T4, T5 and T6). Under 300 mM NaCl salt stress, the transgenic lines TL1, TL2 and TL3 exhibited enhanced salt tolerance, which was stably inherited by their progenies, as well as improved agronomic traits under salt stress, with an average yield reduction of only 8.61%, compared with 34.8% in non-transgenic (NT) control plants. Under salt stress, physiological indices of the transgenic lines showed that ScHAL1 expressed in soybean synergizes with analogous ion transporters to stabilise cytoplasmic K⁺/Na⁺ ratios by reducing Na⁺ influx and promoting K⁺ retention to limit cytosolic Na⁺ toxicity. TL1, exhibiting stable and enhanced salt tolerance through ScHAL1 overexpression, has been approved for environmental release and is currently undergoing biosafety assessment in pre-production field trials. The ScHAL1-overexpressing lines show potential for incorporation into commercial soybean breeding programs aimed at improving salinity tolerance in elite cultivars.