Differential transcript abundance of salt overly sensitive (SOS) pathway genes is a determinant of salinity stress tolerance of wheat

Salt overly sensitive (SOS) pathway genes, SOS1 (plasma membrane Na+/H+ antiporter), SOS2 (CBL interacting protein kinase 24), and SOS3 (calcineurin B like protein 4) are associated with active efflux of toxic sodium ions (Na+) from cytosol and thus confer salinity tolerance in glycophytic plants such as Arabidopsis. The role of SOS pathway genes SOS2 and SOS3 in salinity tolerance of wheat is rarely studied. One-month-old seedlings of three bread wheat genotypes namely, HD 2009, HD2687 and Kharchia 65 were imposed with two levels of salinity stress (100 and 200 mM NaCl) for 30 days duration. Based on the physiological parameters, genotype Kharchia 65 was highly tolerant, HD 2009 was moderately tolerant and HD 2687 was sensitive to salinity stress. Tolerant genotypes accumulated lesser amount of Na+ in root, stem and leaf tissues. Transcript abundance of SOS1, SOS2 and SOS3 genes was significantly higher in salt tolerant genotypes under long-term salinity and correlated with improved sodium exclusion, and higher potassium/sodium (K+/Na+) ratio. Expression levels of genes involved in vacuolar partitioning of Na+, NHX1 (vacuolar Na+/H+ antiporter) and VP1 (Vacuolar pyrophosphatase) were also higher in salt tolerant wheat genotypes under 200 mM NaCl stress. Partial coding sequences of SOS1, SOS2, SOS3, NHX1 and VP1 genes were cloned and sequenced from the above mentioned three wheat genotypes. The results in the present study demonstrated that SOS pathway of ion homeostasis under salinity stress is conserved across species.