Transcriptome profile of Dunaliella salina in Yuncheng Salt Lake reveals salt-stress-related genes under different salinity stresses

Salt stress is an abiotic stress to plants in especially saline lakes. Dunaliella, a halophilic microalga distributed throughout salt lakes and seas, can respond to different salinity stresses by regulating the expression of some genes. However, these genes and their function and biological processes involved remain unclear. Profiling these salt-stress-related genes in a high-salt-tolerant Dunaliella species will help clarify the salt tolerance machinery of Dunaliella. Three D. salina_YC salt-stress groups were tested under low (0.51 mol/L), moderate (1.03 mol/L), and high (3.42 mol/L) NaCl concentrations and one control group under very low (0.05 mol/L) NaCl concentration and 3 transcriptome results that were deep sequenced and de novo assembled were obtained per group. Twelve high-quality RNA-seq libraries with 46 585 upregulated and 47 805 downregulated unigenes were found. Relative to the control, 188 common differentially expressed genes (DEGs) were screened and divided into four clusters in expression pattern. Fifteen of them annotated in the significant enriched Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were validated via qPCR. Their qPCR-based relative expression patterns were similar to their RNA-seq-based patterns. Two significant DEGs, the geranylgeranyl diphosphate synthase coding gene (1 876 bp cDNA) and diacylglycerol O-acyltransferase coding gene (2 968 bp cDNA), were cloned and analyzed in silico. The total lipid content, superoxide dismutase specific activity, and beta, carotene content of D. salina_YC increased gradually with increasing salinity. In addition, the expression of 11 validated genes involved in fatty acid biosynthesis/degradation, active oxygen or carotenoid metabolisms showed significant changes. In addition, algal photochemical efficiency was diminished with increasing salinity, as well as the expression of 4 photosynthesis-related genes. These results could help clarify the molecular mechanisms underlying D. salina responses to the Yuncheng Salt Lake environment and lay a foundation for further utilization of this algal resource.