Genome-Wide Identification of the SiNHX Gene Family in Foxtail Millet (Setaria Italica) and Functional Characterization of SiNHX7 in Arabidopsis

Plant growth is susceptible to abiotic stresses like salt and drought, and Na⁺/H⁺ antiporters (NHXs) play a pivotal role in stress responses. NHX proteins belong to the CPAs (cation/proton antiporters) family with a conserved Na⁺ (K⁺)/H⁺ exchange domain, which is widely involved in plant growth, development, and defense. While <i>NHX</i> genes have been extensively studied in model plants (e.g., <i>Arabidopsis thaliana</i> and <i>Oryza sativa</i>), research in other species remains limited. In this study, we identified nine <i>NHX</i> genes in foxtail millet (<i>Setaria italica</i>) and analyzed their systematic phylogeny, gene structure, protein characteristics, distribution of the chromosome, collinearity relationship, and cis-elements prediction at the promoter region. Phylogenetic analysis revealed that the members of the <i>SiNHX</i> gene family were divided into four subgroups. RT-qPCR analysis of the <i>SiNHX</i> family members showed that most genes were highly expressed in roots of foxtail millet, and their transcriptional levels responded to salt stress treatment. To determine <i>SiNHX7</i>'s function, we constructed overexpression <i>Arabidopsis</i> lines for each of the two transcripts of <i>SiNHX7</i>, and found that the overexpressed plants exhibited salt tolerance. These findings provide valuable insights for further study of the function of <i>SiNHX</i> genes and are of great significance for breeding new varieties of salt-resistant foxtail millet.