Genome-wide identification, molecular characterization, and gene expression analyses of honeysuckle NHX antiporters suggest their involvement in salt stress adaptation

BACKGROUND: Ion homeostasis is an essential process for the survival of plants under salt stress. Na(+)/H(+) antiporters (NHXs) are secondary ion transporters that regulate Na(+) compartmentalization or efflux reduce Na(+) toxicity and play a critical role during plant development and stress responses. METHODS AND RESULTS: To gain insight into the functional divergence of NHX genes in honeysuckle, a total of seven LjNHX genes were identified on the whole genome level and were renamed according to their chromosomal positions. All LjNHXs possessed the Na(+)/H(+) exchanger domain and the amiloride-binding site was presented in all NHX proteins except LjNHX4. The phylogenetic analysis divided the seven NHX genes into Vac-clade (LjNHX1/2/3/4/5/7) and PM-clade (LjNHX6) based on their subcellular localization and validated by the distribution of conserved protein motifs and exon/intron organization analysis. The protein-protein interaction network showed that LjNHX4/5/6/7 shared the same putatively interactive proteins, including SOS2, SOS3, HKT1, and AVP1. Cis-acting elements and gene ontology (GO) analysis suggested that most LjNHXs involve in the response to salt stress through ion transmembrane transport. The expression profile analysis revealed that the expression levels of LjNHX3/7 were remarkably affected by salinity. These results suggested that LjNHXs play significant roles in honeysuckle development and response to salt stresses. CONCLUSIONS: The theoretical foundation was established in the present study for the further functional characterization of the NHX gene family in honeysuckle.