Salt stimulates carbon fixation in the halophyte Nitraria sibirica to enhance growth

Soil salinity significantly inhibits plant productivity by adversely affecting photosynthesis and growth. Nitraria sibirica, a typical halophyte, exhibits strong salt tolerance. In this study, salt-treated Nitraria sibirica seedlings demonstrated more vigorous growth and a higher photosynthetic rate than untreated control seedlings. Transcriptome analysis revealed that the upregulated differentially expressed genes including ribose 5-phosphate isomerase A, ribulose-bisphosphate carboxylase large chain, and malate dehydrogenase in the leaves of Nitraria sibirica treated with 500 mM NaCl were significantly enriched in the 'Carbon fixation in photosynthetic organisms' pathway according to the Kyoto Encyclopedia of Genes and Genomes database. The promoters of these three photosynthetic differentially expressed genes were predicted to contain cis-regulatory elements responsive to light, abscisic acid, and ethylene. Notably, genes encoding 1-aminocyclopropane-1-carboxylate synthase, a key enzyme in ethylene biosynthesis, and ethylene-responsive transcription factors were significantly upregulated in Nitraria sibirica under 500 mM NaCl treatment. Furthermore, quantitative real-time PCR analysis confirmed that the expression of these differentially expressed genes was significantly upregulated in Nitraria sibirica leaves treated with 500 mM NaCl and 500 mM ethephon for 1 h. In contrast, the expression of these salt-induced differentially expressed genes was significantly downregulated in Nitraria sibirica leaves treated with 500 μM aminoethoxyvinylglycine, an ethylene biosynthesis inhibitor, in combination with 500 mM NaCl for 1 h. These findings suggest that the enhanced photosynthesis observed in Nitraria sibirica under salt stress is likely mediated by ethylene signaling, which regulates the expression of genes involved in carbon fixation, thereby promoting vigorous plant growth.