Transcriptomic Profiling Reveals the Contribution of Nitric Oxide to Maintaining Photosynthesis and Antioxidant Ability in Hylotelephium erythrostictum Leaves under Salt Stress

Hylotelephium erythrostictum is a plant species with high garden value and notable salt tolerance, yet the salt tolerance mechanism is poorly understood. In this study, we treated the plants under salt stress with exogenous NO and discovered that the contents of peroxides, such as malondialdehyde (MDA), decreased, while soluble sugars and other osmotic substances increased. The chlorophyll fluorescence parameters, such as the maximum photochemical efficiency of PS II (Fv/Fm), actual quantum yield Y(II), and the photochemical quenching coefficient (qP) increased, whereas the non-photochemical quenching coefficient (NPQ) decreased. Afterthat, we performed transcriptome sequencing on leaves treated with 200 mM NaCl after 0, 5, and 10 d. A total of 124,008 unigenes were identified and functionally annotated. Transcripts related to nitric oxide (NO) synthase exhibited increased expression levels, and transcripts related to superoxide dismutase (SOD) and catalase (CAT) were also significantly upregulated. In contrast, the majority of the differently expressed genes (DEGs) associated with photosynthesis and photosynthesis-antenna protein metabolic pathways were downregulated. Furthermore, the expression levels of HeSOD2, HeCAT2, HeCab1, and HepsaA were significantly upregulated. These results suggest that NO enhances the photosynthetic and antioxidant capacity of H. erythrostictum and improves salt tolerance. Our study will lead to a better understanding of how this plant responds to stressful conditions and potentially develop ways to enhance its salt tolerance by identifying salt-tolerance genes.