Identification and characterization of NHX gene family for their role under salt stress in Vigna mungo

Abstract In the current study, we have performed a comprehensive analysis of the Sodium Hydrogen Exchanger (NHX) gene family in Vigna mungo , and a total of 44 NHX genes were identified. A bimodal distribution based on domains, gene structure and phylogenetic analysis was evident. All intronpoor and intron‐rich genes were clustered in clades I and II, respectively. Interestingly, all genes of subclade IIb were localized to vacuoles and possess only the NHX domain. The isoelectric point and trans‐membrane domain analysis reflect the wide distribution of the NHX genes. Interestingly, Vm_NHX2 and Vm_NHX3 lacked trans‐membrane domain but were found to interact with other NHX genes as well as vital salinity pathway genes, including calcium‐mediated salt‐responsive genes. The comparison of the mRNA sequences with that of V. marina , a halophytic species, reflects their independent evolution, majorly supporting the convergent evolution. The Ka/Ks ratio reflects the abundance of purifying selection supporting their conserved function during evolution. In our analysis, several abiotic stress and hormone‐responsive elements and transcription factor binding sites were present in the promoter of the NHX genes. Further, the ion partitioning of a tolerant (K90) and a susceptible (K49) variety of V. mungo suggested that K90 managed the Na + /K + ratio more affluently, which was also supported by profiling of superoxide radicals, hydrogen peroxide, phenol, peroxidase activity and superoxide dismutase activity. From the expression, we identified five candidate Vm_NHX genes, four of which, i.e. Vm_NHX16 , Vm_NHX17 , Vm_NHX29 and Vm_NHX33 , were localized to the vacuolar and lysosomal membrane.