Ectopic expression of an Ammopiptanthus mongolicus H+-pyrophosphatase gene enhances drought and salt tolerance in Arabidopsis

An orthologue of the vacuolar H+-pyrophosphatase (H+-PPase) gene, AmVP1, was isolated from a desert plant, Ammopiptanthus mongolicus (Leguminosae), by RACE-PCR. AmVP1 has a total length of 2,875 bp, with an open reading frame of 2,316 bp, which encodes a predicted polypeptide of 771 amino acids. Sequence analysis revealed that it has high similarity with the VP1 proteins from other plants. AmVP1 was strongly induced by drought stress, but only responded initially to a salt stress. In addition, a 1.8 kb upstream sequence of AmVP1 was isolated from the genomic DNA of A. mongolicus by TAIL-PCR. Cis-element as well as promoter prediction analysis indicated that it contained three promoter sequences and more than 50 cis-elements. Heterologous expression of AmVP1 in the yeast mutant ena1 could partially suppress its hypersensitivity to NaCl. Over-expressing AmVP1 resulted in enhanced tolerances to both drought and salt stresses in transgenic Arabidopsis plants. The transgenic plants accumulated more sodium and potassium in their leaves after salt stress, and retained more water while producing less malondialdehyde during drought stress. A comparative study of salt tolerance between AtVP1 (an H+-PPase from Arabidopsis) and AmVP1 transgenic Arabidopsis suggested that the efficiency of AmVP1 is more than threefold higher than AtVP1. Our work suggested that AmVP1 functioned as a typical VP1 gene, but might be a more efficient orthologue than AtVP1 and therefore a valuable gene for improving plant salt and drought tolerances.