Overexpression of vacuolar proton pump ATPase (V-H+-ATPase) subunits B, C and H confers tolerance to salt and saline-alkali stresses in transgenic alfalfa (Medicago sativa L.)

The vacuolar proton pump ATPase (V-H+-ATPase), which is a multi-subunit membrane protein complex, plays a major role in the activation of ion and nutrient transport and has been suggested to be involved in several physiological processes, such as cell expansion and salt tolerance. In this study, three genes encoding V-H+-ATPase subunits B (ScVHA-B, GenBank: JF826506), C (ScVHA-C, GenBank: JF826507) and H (ScVHA-H, GenBank: JF826508) were isolated from the halophyte Suaeda corniculata. The transcript levels of ScVHA-B, ScVHA-C and ScVHA-H were increased by salt, drought and saline-alkali treatments. V-H+-ATPase activity was also examined under salt, drought and saline-alkali stresses. The results showed that V-H+-ATPase activity was correlated with salt, drought and saline-alkali stress. Furthermore, V-H+-ATPase subunits B, C and H (ScVHA-B, ScVHA-C and ScVHA-H) from S. corniculata were introduced separately into the alfalfa genome. The transgenic alfalfa was verified by Southern and Northern blot analysis. During salt and saline-alkali stresses, transgenic lines carrying the B, C and H subunits had higher germination rates than the wild type (WT). More free proline, higher superoxide dismutase (SOD) activity and lower malondialdehyde (MDA) levels were detected in the transgenic plants under salt and saline-alkali treatments. Moreover, the ScVHA-B transgenic lines showed greater tolerance to salt and saline-alkali stresses than the WT. These results suggest that overexpression of ScVHA-B, ScVHA-C and ScVHA-H improves tolerance to salt and saline-alkali stresses in transgenic alfalfa.