| In Arabidopsis, overexpression of vacuolar Na+/H+ antiport, AtNHX 1, increases salt tolerance of the plant. Genomic DNA database search indicates that there are four other genes that are homologous to AtNHX1.; In this thesis, the cloning and characterization of AtNHX3 is reported. The ORF of AtNHX3 is about 1.5 kb, coding for 521 amino acids. AtNHX3 protein shares about 35% identical sequence with AtNHX1 and AtNHX2. Western blotting shows that AtNHX3 is located on tonoplast. Northern-blotting and semi-quantitative RT-PCR suggest that AtNHX3 mRNA is in root, stem, leaf and flower, and there is no significant difference for mRNA levels between young seedlings and adult plants. Furthermore, AtNHX3 mRNA levels do not change in response to salt treatment. AtNHX3 can complement a yeast salt sensitive mutant, Deltanhx1, and overexpression of AtNHX3 in Arabidopsis greatly increases salt tolerance of the plant. Yeast complementation studies suggest that C-terminus of AtNHX3 is necessary for the full function of this antiport. |
