Objective Sesuvium portulacastrum, a typical coastal and mangrove associate plant, is capable of retaining sand and protecting banks. It can grow normally in seawater and has a strong salt tolerance. Na⁺/H⁺ exchange (NHX) plays a key role in salt tolerance and plant growth with development. In order to understand the role of NHX in salt tolerance of S. portulacastrum, the NHX genes were identified and analyzed.

Method In this study, the S. portulacastrum NHX genes were identified by using informatic method through its full length transcriptome data. Their physicochemical properties, conserved motifs and evolutionary relationships were analyzed, and the expression patterns of NHX genes under s alt stress were studied by quantative real-time PCR (qRT-PCR).

Result The results showed that 12 SpNHX genes were identified from S. portulacastrum and named as SpNHX1 to SpNHX12. The number of amino acids ranged from 276 to 554, with the molecular weight ranged from 31.22 to 61.21 kD, isoelectric point from 5.55 to 8.64, and instability ind ex from 32.14 to 50.54. All the proteins were hydrophobic. Phylogenetic analysis showed that SpNHX proteins can be divided into two subgroups. Similar conserved motifs composition was found in each subgroup. Multiple sequence alignment results showed that all SpNHX proteins had Na⁺/H⁺ exchange conserved domains. RNA-seq data and qRT-PCR results showed that SpNHX genes were induced to different degrees under salt stress, and SpNHX1, SpNHX9, SpNHX10, SpNHX11 and SpNHX12 were significantly up-regulated under salt stress.

Conclusion This study clarified the expression patterns of NHXs in S. portulacastrum under high salt stress, indicating that SpNHX1, SpNHX9, SpNHX10, SpNHX11 and SpNHX12 may be involved in the response of S. portulacastrum to salt stress, which provided a theoretical basis for further research on the role of NHX in the process of salt tolerance of S. portulacastrum.