Overexpressing BvNHX1, AtNHX5 Improved Salt Tolerance Of Arabidopsis Thaliana

Salt stress disrupts homeostasis in ion distribution of plant cell. High levels of sodium ion(Na~+) in the cytoplasm are toxic to plants because of their adverse effects on celluarmetabolism. One important strategy for plants to improve salt tolerance is to re-establish theionic homeostasis. Ionic homeostasis including Na~+ entry, efflux, sequestration and longdistance transport. Maintaining a low Na~+,high K~+ state is a basic strategy for plants totolerate high soil salinity. The most direct way to maintain low cytoplasmic Na~+ is tosequester it in vacuoles within each plant cell. Na~+ compartmentation is important for plant salttolenrance and Na~+ sequestration into the vacuole depends on expression and activity ofNa~+/H~+ antiporters as well as on V-type H~+-ATPase and H~+-PPase. These phosphatasesgenerate the necessary proton gradient required for activity of Na~+/H~+ antiporters.Theimportance of vacuolar sequestration to plant salinity tolerance has been underlined byexperiments in which constitutive overexpression of vacuolar transporters has greatly increasedsalinity tolerance of a range of species.BvNHX1 from Beta vulgaris, encodes a vacuolar Na~+/H~+antiporter and may play important roles in ion homeostasis.In this research, BvNHX1 (1659 bp), AtNHX5 (1554bp) were inserted into binary plantvector pROKII. The resulting plasmids were mobilized to Agrobacterium tumefaciens strainGV3101 used for plant transformation. The genes were introduced into Arabidopsis thaliana(ecotype Columbia) by Agrobaterium tumefaciens-mediated transformation withfloral-dipping method under the control of CaMV 35S promoter. Transformants were selectedfor their ability to grow on medium containing kanamycin (40mg/L). Several homozygouslines transformed with BvNHX1 and AtNHX5 were selected and used for further molecularand physiological determination. Whether the genes were transformed into the Arabidopsiswas confirmed by Southern blotting and Northern blotting.Molecular and physiological determination result of BvNHX1 and AtNHX5 homozygoustransformants:1. Southern blotting analysis indicated that BvNHX1 and AtNHX5 genes had beenintegrated into the transgenic plants'genomes. The copy numbers of the gene in transgenicplants were different.2. Northern analysis revealed the expression of BvNHX1 and AtNHX5 gene in T3 plants ofseveral non-segregation transgenic lines. While the different lines have different expressivesignals.3. The transgenic plants grew more vigorously after NaCl treatment of differentconcentrations than wild type plants.4. The fresh weight and the dry weight of the transgenic lines were much higher than thatof wildtype plants under different concentrations of NaCl treatment.5. Transgenic plants showed a tendency to accumulate more Na+ and K+ under salineconditions than wild type plants.6. The transgenic plants grew more vigorously on the MS medium with differentconcentrations of NaCl.Summarily, overexpressing of BvNHX1 and AtNHX5 gene improved salt tolerance oftransgenic plants.