Nitric oxide modulating ion balance in Hylotelephium erythrostictum roots subjected to NaCl stress based on the analysis of transcriptome, fluorescence, and ion fluxes

Soil salinization is one of the main stress factors that affect both growth and development of plants. Hylotelephium erythrostictum exhibits strong resistance to salt, but the underlying genetic mechanisms remain unclear. In this study, hydroponically cultured seedlings of H. erythrostictum were exposed to 200 mM NaCl. RNA-Seq was used to determine root transcriptomes at 0, 5, and 10 days, and potential candidate genes with differential expression were analyzed. Transcriptome sequencing generated 89.413 Gb of raw data, which were assembled into 111,341 unigenes, 82,081 of which were annotated. Differentially expressed genes associated to Na⁺ and K⁺ transport, Ca²⁺ channel, calcium binding protein, and nitric oxide (NO) biosynthesis had high expression levels in response to salt stress. An increased fluorescence intensity of NO indicated that it played an important role in the regulation of the cytosolic K⁺/Na⁺ balance in response to salt stress. Exogenous NO donor and NO biosynthesis inhibitors significantly increased and decreased the Na⁺ efflux, respectively, thus causing the opposite effect for K⁺ efflux. Moreover, under salt stress, exogenous NO donors and NO biosynthesis inhibitors enhanced and reduced Ca²⁺ influx, respectively. Combined with Ca²⁺ reagent regulation of Na⁺ and K⁺ fluxes, this study identifies how NaCl-induced NO may function as a signaling messenger that modulates the K⁺/Na⁺ balance in the cytoplasm via the Ca²⁺ signaling pathway. This enhances the salt resistance in H. erythrostictum roots.