Transcriptome assembly and differential gene expression analysis of Podocarpus macrophyllus in response to salt stress

Podocarpus macrophyllus, an ancient Gymnosperm species, has a unique environmental adaptation strategy which can be attributed to its lengthy evolutionary process. In this study, we used different concentrations of NaCl solution to treat P. macrophyllus seedlings and evaluated their salt tolerance. We investigated the physiological and molecular responses in P. macrophyllus plants to salt stress by analyzing their photosynthetic system and antioxidant enzyme activity. In addition, we analyzed the transcriptional responses to salt stress by RNA sequencing and transcriptome assembly. Our results showed that the photosynthetic system was significantly affected by saline treatment, which decreased the chlorophyll content, altered chloroplast ultrastructure, and reduced photosynthesis. Furthermore, the activities of antioxidant enzymes increased significantly following salt stress treatment. Transcriptome analysis showed that the expression of a large number of genes was induced by salt stress, and these genes were mainly involved in multiple metabolic and biological regulation processes. Moreover, the expression levels of genes that were mediated by phytohormone transport and signaling were altered. The K+ and Ca+ transporter-encoding genes were upregulated in response to salt stress, as were the MYB transcription factor genes involved in abiotic stress. However, the genes involved in cell wall biosynthesis and secondary metabolism were downregulated. Our research provides a reference for further utilization of the gene resource of P. macrophyllus to improve salt stress tolerance in crops.