Physiological and Transcriptional Regulation of Salt Tolerance in Thinopyrum ponticum and Screening of Salt-Tolerant Candidate Genes.

The tall wheatgrass Thinopyrum ponticum has excellent saline-alkali tolerance and great potential for restoring saline-alkali land to enhance productivity. This study used the Thinopyrum ponticum cv. "Orbit" variety, which is widely planted in saline-alkali pastures, as the material and artificially simulated salt stress using 150 mM NaCl and 150 mM Na2SO4, respectively. The growth and physiological indexes of the leaves and roots of seedlings were measured after various treatment durations, and the transcriptomes of untreated and Na2SO4-treated leaves and roots were also analyzed after 24 h of treatment. The results showed that salt stress resulted in significant reductions in leaf relative water content in seedlings and inhibited root elongation growth, with Na2SO4 treatment producing a greater impact on plant growth than NaCl treatment. Salt stress significantly alters ion transport and distribution in Thinopyrum ponticum, characterized by pronounced Na+ accumulation and a concomitant decline in K+ uptake. Additionally, to adapt to salt stress, roots enhance their ability to absorb and transport essential cations, such as Ca2+, Mg2+, Fe3+, and Cu2+. RNA-Seq analysis identified 1682 and 2816 differentially expressed genes (DEGs) in leaves and roots under Na2SO4 stress, respectively, with 210 common DEGs. Enrichment analyses revealed that DEGs were primarily associated with redox homeostasis, ion balance, and signal transduction. Furthermore, transcription regulation analysis indicated the Thinopyrum ponticum can coordinate the activation of NAC/MYB/WRKY transcription factors, SA/ETH hormone signaling, and Ca2+ pathways in response to salt stress. In summary, this study systematically reveals for the first time the molecular mechanisms by which Thinopyrum ponticum responds to Na2SO4 stress through coordinated regulation of ion transport, transcription factor networks, and hormone-Ca2+ signaling pathways. Based on transcriptomic and protein-protein interaction analyses, nine key candidate genes for saline-alkali tolerance were identified, including UGT7472, JMT, T4E14.7, CAX5, CP1, PXG2 NAMT1, BON3, and APX7. These findings provide novel genetic resources and a theoretical foundation for breeding salt-alkali-tolerant crops.