Transcriptome sequencing of Antarctic moss under salt stress emphasizes the important roles of the ROS-scavenging system

Mosses are predominant terrestrial vegetation in Antarctica. Their distributions appear to be controlled more by water and salinity. The Antarctic moss Pohlia nutans can tolerate high salt stress. Here, high-throughput sequencing was employed to study the transcriptional characteristics of P. nutans under salt stress. Differentially expressed genes (DEGs) analysis showed that 1340 genes were significantly upregulated and 831 genes were markedly downregulated. The expression of representative DEGs including abscisic acid (ABA) and Jasmonates (JAs) pathway-related genes, antioxidant enzyme genes, and flavonoid biosynthesis-related genes were analyzed by real-time PCR and most were upregulated after salt stress. Furthermore, malondialdehyde (MDA) content was significantly increased after salt treatment. The levels of hydroxyl free radical (OH) first rose then quickly decreased. In addition, the activities of antioxidant enzymes, such as catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), and the flavonoid content were enhanced after salt stress. Exogenous application of ABA, Methyl jasmonate (MeJA) or proanthocyanidins (PA) improved the performance of P. nutans in response to high salt stress. Furthermore, real-time PCR showed that ABA or MeJA treatment upregulated the gene expression of antioxidant and flavonoid biosynthesis-related enzymes. These results suggest that the responses of P. nutans under salt stress are involved in activating phytohormone signaling pathways which trigger two main antioxidant defense systems (i.e., antioxidant enzymes and flavonoids) for protecting cell and scavenging reactive oxygen species.