Genotype-dependent salt tolerance mechanisms in wheat–Thinopyrum introgression lines revealed by ion transporter gene expression and seedling phenotyping

Soil salinity significantly impairs wheat growth and yield worldwide. Wild relatives of wheat, such as Thinopyrum species, harbor valuable salt tolerance traits that can improve cultivated wheat via introgression. This study investigates the salt tolerance of three wheat-Thinopyrum introgression lines and their wheat parents during germination under salt stress (0, 100, 200 mM NaCl). Molecular cytogenetic analyses confirmed the presence and stability of Thinopyrum chromatin in these lines. Morphophysiological traits, including germination rate, radicle and coleoptile length, root system architecture, and biomass were assessed. Salt stress curtailed root and shoot growth across genotypes, though Thinopyrum introgression lines showed varied resilience. Gene expression patterns of key ion transporters (HKT, SOS, NHX) involved in Na+ exclusion and homeostasis were also evaluated in radicle and coleoptile tissues. Results showed significant genotype-dependent differences, with the 3St(3D) substitution line exhibiting strong upregulation of TaSOS1 and TaNHX1 linked to improved salt tolerance mechanisms. Coordinated expression of ion transporter genes suggests enhanced sodium extrusion and sequestration pathways in tolerant genotypes. These findings highlight the potential of wheat-Thinopyrum introgression lines as genetic resources for breeding salt-tolerant wheat cultivars.