Overexpression of a vacuolar H+-pyrophosphatase and a B subunit of H+-ATPase cloned from the halophyte Halostachys caspica improves salt tolerance in Arabidopsis thaliana

To avoid the effects of Na+ toxicity, plants have developed mechanisms to sequester Na+ in vacuoles. This sequestration process is catalyzed by a vacuolar Na+/H+ antiporter, with the transmembrane electrochemical potential initially established by the tonoplast H+-ATPase and H+-pyrophosphatase (H+-PPase). In this study, we cloned HcVP1 and HcVHA-B encoding a vacuolar H+-PPase and a B subunit of H+-ATPase, respectively, from Halostachys caspica, a succulent shrub that is highly salt-tolerant and widely distributed in Central Asia. The cDNA of HcVP1 is 2,295 bp and contains an open reading frame (ORF) of 764 amino acids and the HcVHA-B cDNA is 1,467 bp with an ORF of 488 amino acids. Semi-quantitative PCR revealed that transcription of both genes in H. caspica is induced by salt stress. Additionally, increased seed germination and improved plant growth were observed in transgenic Arabidopsis thaliana plants heterologously expressing HcVP1 or HcVHA-B, relative to wild-type plants when grown in the presence of NaCl. Specifically, Na+ content in leaves of transgenic Arabidopsis plants was higher than in wild-type leaves. These results demonstrate that overexpression of a vacuolar H+-PPase and a B subunit of H+-ATPase from H. caspica may enhance salt tolerance in transgenic Arabidopsis through increased accumulation of Na+ in vacuoles.