Abstract
BackgroundSoil salinity adversely affects plant growth and development and disturbs intracellular ion homeostasis resulting cellular toxicity. The Salt Overly Sensitive 1 (SOS1) gene encodes a plasma membrane Na+/H+ antiporter that plays an important role in imparting salt stress tolerance to plants. Here, we report the cloning and characterisation of the SbSOS1 gene from Salicornia brachiata, an extreme halophyte.ResultsThe SbSOS1 gene is 3774 bp long and encodes a protein of 1159 amino acids. SbSOS1 exhibited a greater level of constitutive expression in roots than in shoots and was further increased by salt stress. Overexpressing the S. brachiata SbSOS1 gene in tobacco conferred high salt tolerance, promoted seed germination and increased root length, shoot length, leaf area, fresh weight, dry weight, relative water content (RWC), chlorophyll, K+/Na+ ratio, membrane stability index, soluble sugar, proline and amino acid content relative to wild type (WT) plants. Transgenic plants exhibited reductions in electrolyte leakage, reactive oxygen species (ROS) and MDA content in response to salt stress, which probably occurred because of reduced cytosolic Na+ content and oxidative damage. At higher salt stress, transgenic tobacco plants exhibited reduced Na+ content in root and leaf and higher concentrations in stem and xylem sap relative to WT, which suggests a role of SbSOS1 in Na+ loading to xylem from root and leaf tissues. Transgenic lines also showed increased K+ and Ca2+ content in root tissue compared to WT, which reflect that SbSOS1 indirectly affects the other transporters activity.ConclusionsOverexpression of SbSOS1 in tobacco conferred a high degree of salt tolerance, enhanced plant growth and altered physiological and biochemical parameters in response to salt stress. In addition to Na+ efflux outside the plasma membrane, SbSOS1 also helps to maintain variable Na+ content in different organs and also affect the other transporters activity indirectly. These results broaden the role of SbSOS1 in planta and suggest that this gene could be used to develop salt-tolerant transgenic crops.
Highlights
Soil salinity adversely affects plant growth and development and disturbs intracellular ion homeostasis resulting cellular toxicity
The SbSOS1 protein sequences were compared with the conserved domain in NCBI database and two conserved regions were identified: Nhap, an Na +/H+ antiporter spanning the transmembrane domain and a cyclic nucleotide-binding domain that is located at the C-terminal tail (Figure 1a)
Amino acid alignments of the SbSOS1 sequence revealed a high degree of similarity to Suaeda japonica SjSOS1 (90%), Chenopodium quinoa CqSOS1 (83%), Mesembryanthemum crystallinum McSOS1 (75%), Populus euphratica PeSOS1 (68%), Solanum lycopersicum SlSOS1 (66%), Oryza sativa OsSOS1 (62%), Thellungiella halophila ThSOS1 (61%), Brassica napus BnSOS1 (61%), Triticum aestivum TaSOS1 (60%) and Arabidopsis thaliana AtSOS1 (57%) (Additional file 1: Figure S2)
Summary
Soil salinity adversely affects plant growth and development and disturbs intracellular ion homeostasis resulting cellular toxicity. High salinity adversely affects plant growth and development by disturbing intracellular ion homeostasis, molecular networks that regulate stress perception, signal transduction and the expression of both stressrelated genes and metabolites. NHX1 are located in tonoplasts and reduce cytosolic Na+ concentration by pumping in the vacuole [10], whereas SOS1 is localised at the plasma membrane and extrudes Na+ in apoplasts [11]. Both of these antiporters are driven by the proton motive force generated by the H+-ATPase [12]
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