Arabidopsis Calcium/Hydrogen Antiporter Protein (AtChaC3), Enhances the Tolerance to Salinity and Drought Stresses

Sequestration of Na⁺ from the cytosol into vacuoles, coordinated by the vacuolar Na⁺/H⁺ antiporter proteins, is considered an important salt tolerance mechanism in plants. In Escherichia coli, resistance and adaptation to increased concentration of Na⁺ or Ca²⁺ is mediated by the action of the Ca²⁺/H⁺ antiporter proteins (ChaA). Another class of these proteins, known as ChaC-like proteins, is thought to be associated with the putative ChaA proteins, but their exact function remained largely uncharacterized. In this study we the investigated the effects of overexpression of three Arabidopsis AtChaC genes on tolerance to salt and drought stresses. Arabidopsis AtChaC1, AtChaC2 and AtChaC3 were cloned into pEarleyGate plant expression vectors and used to develop transgenic Arabidopsis via Agrobacterium-mediated gene transfer. Integration and successful overexpression of the transgenes were confirmed by genome PCR and western blot analysis, respectively. For subcellular localization, genes were cloned individually into the binary vector pCAMBIA 1300 containing a 35S::sGFP cassette to create ChaC-sGFP fusion proteins. Transgenic and control plants were subjected to salt or drought stress.  Subcellular localization determined that the three genes as membrane binding proteins. Under either salt or drought stresses, only the transgenic plants overexpressing AtChaC3 exhibited enhanced tolerance in term of significantly greater fresh and dry weights. These results suggest that AtChaC3, but not AtChaC1 or AtChaC2, may play important role in tolerance to salt and drought stresses.