Transgenic Expression of Prunus persica Salt Overly Sensitive 2 (PpSOS2) in the atsos2 Mutant Imparts Salt Tolerance in Arabidopsis

Salinity is one of the main environmental stresses that negatively affect crop productivity. Almond trees are sensitive to salt stress; however, salinity-tolerant rootstocks can significantly enhance crop production under saline conditions. This work reports the functional complementation of the Prunus persica Salt Overly Sensitive 2 (PpSOS2) gene from the almond rootstock "Nemaguard" in the Arabidopsis thaliana atsos2 mutant. Two transgenic lines of PpSOS2 developed using constitutive (PpSOS2.OE3.5) and endogenous (PpSOS2NP.2.7) promoters showed significantly higher germination, survival rates, and dry weight than atsos2 under 90 mM NaCl treatment. The atsos2 mutant displayed the inhibition of primary and lateral roots under 50 mM NaCl. The root growth inhibition was restored by PpSOS2 complementation. Both transgenic lines showed a significant decrease in electrolyte leakage compared to atsos2 under 50 mM NaCl. The expression analysis of six K+-rectifying channel genes and a reactive oxygen species-specific gene revealed the differential expression of AtCHX14 and AtCHX13 genes in transgenic lines compared to atsos2 24 h after the 50 mM NaCl treatment. These observations suggest that PpSOS2 modulates and restores salt tolerance in atsos2. Also, in Prunus, the SOS pathway is conserved, suggesting that the exclusion of Na+ is an important component trait for salt tolerance.