Genome-wide identification and expression profiling of the NHX gene family in oat (Avena sativa L.)

Salt stress imposes osmotic imbalance and ion toxicity, severely impairing crop growth and development. Na⁺/H⁺ antiporters (NHXs) play a central role in salt tolerance by mediating sodium transport across cellular membranes. We conducted a genome-wide characterization of the NHX gene family in four hexaploid oat cultivars, identifying 126 NHX genes. These were grouped into 33 orthologous gene groups (OGGs), comprising 10 core and 23 dispensable OGGs. The naked oat cultivar ‘Sanfensan (SFS)’ contained the largest number of both total and core NHX genes. Phylogenetic analysis classified AsNHX genes into three classes: vacuolar (Vac-class), endosomal (Endo-class), and plasma membrane (PM-class). Ka/Ks analysis indicated strong purifying selection across most members. Cis-regulatory element analysis revealed abundant stress-related motifs, including abscisic acid (ABA) and methyl jasmonate (MeJA) response elements, suggesting roles in abiotic stress adaptation. Transcriptome and qRT-PCR data confirmed that AsNHX1/3/7/9/14/23/24/25/32 were up-regulated under salt stress, highlighting their importance in salinity tolerance. This study provides the first comprehensive characterization of the AsNHX gene family, detailing their evolutionary, structural, and functional features. The findings offer critical insights into salt adaptation mechanisms in oat and identify promising targets for genetic improvement of salinity tolerance.