Analysis of salt resistance conferred by salt overly sensitive 3 protein from mulberry (Morus notabilis)

Recombinant E. coli expressing MnSOS3 showed enhanced growth (maximum OD₆₀₀ = 0.338) vs. near-zero growth in the control. Transgenic tobacco line MnSOS3-2 (highest expression) exhibited 33.3% survival under 300 mM NaCl, 2.5-fold higher than wild-type (WT, 13.3%). Transgenic leaves accumulated 54.8% less Na⁺ (0.95 ± 0.02 vs. 2.10 ± 0.07 mmol/g FW) and 45.8% more K⁺ (1.75 ± 0.02 vs. 1.20 ± 0.02 mmol/g FW) than WT, leading to a 67.8% lower Na⁺/K⁺ ratio (0.55 ± 0.01 vs. 1.71 ± 0.08). The yeast two-hybrid assay confirmed MnSOS3-MnSOS2 interaction. These findings show MnSOS3 boosts salt tolerance via Na⁺/K⁺ homeostasis and SOS pathway activation, a key resource for salt-tolerant mulberry breeding.