Functional Characterization Of Two Apple Tonoplast Proton Pump Genes H~+-PPase And H~+-ATPase Subunit A In Stress Tolerance

Vacuolar H~+-translocating inorganic pyrophosphatase (VHP, EC3.6.1.1) and vacuolarH~+-translocating ATPase (VHA) as plant proton pump play a very important role in the plantgrowth and development both under normal and stress conditions. In this study, two protonpump genes MdVHP1and MdVHA-A were isolated from apple. Their fuctions in the toleranceto abiotic stresses were characterized with expression analyses and genetic transformation.The main results were shown as follows:1. MdVHP1and MdVHA-A were induced by salt, drought, cold and heat in apple in vitroshoot cultures. But it showed that MdVHP1and MdVHA-A showed different expressionpattern in response to different abiotic stresses2. MdVHP1overexpression enhanced tolerance to salt, drought, cold and heat intransgenic apple calluses, by increasing proline accumulation and decreasing MDA contentcompared with control calluses. Therefore, MdVHP1overexpression reduced membranedamage in transgenic apple calluses to improve resistance.In addition, MdVHP1overexpression enhanced tolerance to salt and drought,byincreasing accumulation of Na~+, K~+, enhancing RWC and decreasing solute potentialcompared with wild type. Therefore, MdVHP1improve ability of salt and drought resistancethrough ion regional and osmotic regulation in tomato plants.3. Transgenic tobacco lines over-expressing MdVHA-A were resistant to drought andsalinity than non-transgenic plants. MdVHA-A overexpression improved tolerance to salinityin transgenic tobacco, along with higher Na~+, K~+uptake and higher proline and lower MDA inleaf tissues. MdVHA-A overexpression improved tolerance to drought in transgenic tobacco,along with high RWC, proline, low MDA compared with non-transgenic tobacco. Theseresults suggest MdVHA-A overexpression improve resistance to drought and salinity thannon-transgenic plants through ion vacuole accumulation and osmotic adjustment. In addition,MdVHA-A overexpression could promote lateral root growth of transgenic tobacco andincrease drought resistance through the change of auxin content.These results indicate that MdVHA-A and MdVHP1are involved in plant stress responses, and suggest that MdVHA-A and MdVHP1are useful candidate genes for improvingdrought and salt tolerance in the plant.