Research Of Co-expression Of ScNHX1 And ScVP In Transgenic Hybrids Improves Salt And Saline-alkali Tolerance In Alfalfa

Abiotic stress tolerance is a complex trait that involves tolerances to salinity, extreme temperatures, soil drought or limited mineral nutrients. The combinations and severity of these stresses that crops must tolerate vary with environment and year. Vacuolar Na+/H+ antiporter, which catalyze the exchange of Na+ for H+ across tonoplast membranes. H+-PPase is an electrogenic proton pump that translocates protons into vacuoles in plant cells. Overexpression of vacuolar Na+/H+ antiporter gene (NHX1) or vacuolar H+-PPase (V-PPase) confer salt tolerance in a wide variety of plants. In this study, co-expressing ScNHX1 and ScVP transgenic alfalfa were raised from sexual crosses between ScNHX1- and ScVP-transgenic alfalfa plants that had been screened for improved tolerance of salt and saline-alkali stress. The main results are as follow:1. It was shown that T1 progeny of alfalfa expressing either the vacuolar membrane Na+/H+ antiporter gene from Suaeda corniculata (ScNHX1) or the S. corniculata vacuolar H+-PPase gene (ScVP) had significantly higher salt and saline-alkali stress tolerance compared with non-transgenic siblings.2. Alfalfa plants transgenic for both ScNHX1 and ScVP were produced by cross-pollination. Northern blot analysis revealed that salt and saline-alkali stresses increased the level of ScNHX1 and ScVP transcripts in alfalfa leaves.3. Transgenic alfalfa plants co-expressing ScNHX1 and ScVP showed enhanced salt and saline-alkali tolerance of 300 mmol/L NaCl or 200 mmol/L NaCl with 100 mmol/L NaHCO3 treatments, compared with transgenic plants expressing only ScNHX1 or ScVP.4. Compared with wild-type alfalfa, transgenic plants co-expressing ScNHX1 and ScVP accumulated more Na+ in leaves and roots and showed increased tolerance to higher salt and saline-alkali stresses.5. Using the fluorescent carboxy-SNARF probe, the intracellular pH was visualized in the transgenic and wild-type plants under salt and saline-alkali stresses. The results showed that vacuolar alkalization and acidification differed significantly in cells of the transgenic and wild-type alfalfa plants. Collectively, our results indicate that co-expression of multiple, effective genes in transgenic plants can effectively enhance resistance to abiotic stresses.