Enhanced salinity tolerance in transgenic mungbean overexpressing Arabidopsis antiporter (NHX1) gene

Efficient compartmentalization of Na+ ions into the vacuole through heterologous overexpression of vacoular antiporter gene NHX1 is a promising approach to develop salt tolerance in plants. Mungbean (Vigna radiata L. Wilczek) is an important grain legume widely cultivated in Southeast Asia for its protein rich grains. Salinity affects growth and productivity of mungbean. In this paper, we report overexpression of an Arabidopsis NHX1 (AtNHX1) in transgenic mungbean plants conferred enhanced salt tolerance. Cotyledonary node explants were transformed via Agrobacterium tumefaciens mediated transformation using pCAMBIA2301 vector that harbours 35S:: AtNHX1 in its T-DNA. Putative transformed plants were selected on kanamycin containing medium. Polymerase chain reaction and Southern blot analysis confirmed the presence, integration and copy number of transgenes in T-1 transgenic lines. Reverse transcription-PCR analysis showed higher expression of AtNHX1 in transgenic plants as compared to wild type plants (WT). Under salt stress conditions, T-2 transgenic lines displayed less damage and stronger growth phenotypes with concurrent physiological changes as compared to WT. In addition, T-2 transgenic lines under salt stress accumulated higher K+/Na+ in the aerial parts and higher [Na+] in roots than WT. Moreover, the T-2 transgenic lines showed under NaCl treatment reduced membrane lipid peroxidation and H2O2 and O-2(-) accumulation, higher levels of antioxidant enzyme activity and increased accumulation of proline and ascorbate than WT. These results indicated that the activity of heterologous AtNHX1 protein contributing enhanced salt tolerance in transgenic mungbean.