Novel Vacuolar Na+/H+ Antiporters Of Cowpea And Mungbean Confer Salt Tolerance In Transgenic Plants

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Cowpea (Vigna unguiculata L. Walp.) and mungbean (Vigna radiata L. Wilczek) are two important grain legumes that supply vegetable proteins in nutritionally deprived regions of the world. Cowpea and mungbean are cultivated mainly in the semi-arid and arid regions of Africa, India, Middle East, South America, Southern Europe and USA. However, their sustainable agricultural production worldwide is limited by salt salinity. Plant Na+/H+ antiporters play a major role in maintaining cellular homeostasis under salinity stress. Vacoular Na+/H+ antiporters compartmentalize excess cytosolic Na+ into vacuole thereby reduce ionic toxicity in cytosol and assist in maintaining cellular homeostasis and ionic equilibrium. Isolation and functional characterization of vacuolar Na+/H+ antiporters from many glycophytes and halophytes have clearly indicated the role of vacuolar NHX in salt tolerance mechanisms. We report for the first time, the cloning and functional characterization of vacuolar Na+/H+ antiporters of cowpea (VuNHX1) and mungbean (VrNHX1). The VuNHX1 (Genbank Acc. No. JN641304.2) cDNA is 1981 bp and VrNHX1 (Genbank Acc. No. JN656211.1) cDNA is 2095 bp, both consist of an ORF of 1629 bp encoding a polypeptide of 542 amino acid residues, with a deduced molecular mass of 59.6 kDa. VuNHX1 and VrNHX1 displayed a conserved amiloride binding domain (84LFFIYLLPPI93) in their third transmembrane (TM3) region. Sequence alignment and phylogenetic analysis revealed VuNHX1 and VrNHX1 belong to Class-I clade of plant NHX exchangers and have high similarity with legume Na+/H+ antiporters. Southern hybridization indicated presence of single copy of VuNHX1 and VrNHX1 in respective genomes.
Supervisor: Lingaraj Sahoo