Co-expression of SpSOS1 and SpAHA1 in transgenic Arabidopsis plants improves salinity tolerance

Na+ extrusion from cells is important for plant growth in high saline environments. SOS1 (salt overly sensitive 1), an Na+/H+ antiporter located in the plasma membrane (PM), functions in toxic Na+ extrusion from cells using energy from an electrochemical proton gradient produced by a PM-localized H+-ATPase (AHA). Therefore, SOS1 and AHA are involved in plant adaption to salt stress. In this study, the genes encoding SOS1 and AHA from the halophyte Sesuvium portulacastrum (SpSOS1 and SpAHA1, respectively) were introduced together or singly into Arabidopsis plants. The results indicated that either SpSOS1 or SpAHA1 conferred salt tolerance to transgenic plants and, as expected, Arabidopsis plants expressing both SpSOS1 and SpAHA1 grew better under salt stress than plants expressing only SpSOS1 or SpAHA1. In response to NaCl treatment, Na+ and H+ in the roots of plants transformed with SpSOS1 or SpAHA1 effluxed faster than wild-type (WT) plant roots. Furthermore, roots co-expressing SpSOS1 and SpAHA1 had higher Na+ and H+ efflux rates than single SpSOS1/SpAHA1-expressing transgenic plants, resulting in the former amassing less Na+ than the latter. As seen from comparative analyses of plants exposed to salinity stress, the malondialdehyde (MDA) content was lowest in the co-transgenic SpSOS1 and SpAHA1 plants, but the K+ level was the highest. These results suggest SpSOS1 and SpAHA1 coordinate to alleviate salt toxicity by increasing the efficiency of Na+ extrusion to maintain K+ homeostasis and protect the PM from oxidative damage induced by salt stress.