Genome-wide analysis of the Actinidia chinensis NHX family and characterization of the roles of AcNHX3 and AcNHX7 in regulating salt tolerance in Arabidopsis

Soil salinization, which leads to the excessive accumulation of Na+ in plants, affects plant growth and development and reduces the yield of fruit crops. To minimize Na+ toxicity, the Na+/H+ antiporters (NHX) mediate the transport of Na+ into vacuoles to promote Na+ compartmentalization or reduce the Na+ concentration in the cytoplasm by promoting Na+ efflux. NHX family members have been identified in many plant species. However, few studies have reported on NHX family members in kiwifruit. In this study, eight NHX family members were identified in the Actinidia chinensis genome. These AcNHXs were clustered into three groups based on phylogenetic analysis. Further analysis of gene structures and conserved motifs of these AcNHX proteins supported the clustering patterns. Collinearity analysis showed that segmental duplication has played an important role in the expansion of the AcNHX family. Multiple cis-acting elements involved in abiotic stress or hormonal responses were detected in the promoters of AcNHX genes. Gene expression analysis revealed that the responses of AcNHXs to salt stress varied. AcNHX3 and AcNHX7 were shown to play a role in regulating salt tolerance in yeast and Arabidopsis, respectively. These findings provide valuable information for future studies aimed at examining the roles of AcNHX proteins in regulating salt tolerance in kiwifruit, as well as the underlying molecular mechanisms.