Genome-wide identification, structural characterization and phylogenetic analysis of NHX (Na+/H+ exchanger) in Lima bean (Phaseolus lunatus L.)

The Na+/H+ exchanger (NHX), a gene family of membrane transporters, is well recognized for enhancing salt tolerance in plants. The NHXs assist in maintaining ion and pH homeostasis in cells by exchanging K+ or Na+ for H+. Genome-wide analysis of NHX genes has not been reported in lima bean. The current study aimed at exploring and characterizing the NHX gene family across the genome of the lima bean. Eight PlNHX genes in the genome of lima bean were detected during the present study, and named as PlNHX1-PlNHX8 on the basis of predicted sub-cellular localization. PlNHX8 was recorded as the largest gene while PlNHX5 was found as the smallest gene based on their CDS, protein length (PL) and protein molecular weight (PMW). Similarly, Isoelectric points and GRAVY were found in the range of 5.33 to 9.18 and 0.111 to 0.647, respectively. Vacoule was predicted as a major residence for PlNHX proteins. The varying number of exons reveals that events like deletion/addition have resulted in variation in motif number during the course of evolution, with motif3 conserved in all PlNHX genes. Phylogenetic tree reveals that paralogs contributed 25% to the PlNHX gene family expansion. Ka/Ks ratios of paralogs reveal that they were all under purifying selection. The promoter region has Box-4, G-box, ABRE and MeJA might be contributing elements for growth, development and defence functions of PlNHX. This study provides a basis for the functional validity of PlNHX genes.