No abstract

Background: The brine shrimp Artemia salina can thrive in a variety of salinities and is commonly distributed in natural hypersaline lakes and solar salterns. The zooplankter A. salina proves to be a filter feeder, consuming the alga Dunaliella and prokaryotes and plays a critical role in the hypersaline food web. However, the high salinity adaptation mechanisms of A. salina remain poorly understood through transcriptome analysis. Here, we examined the gene expression patterns of A. salina adults that were salt-adapted for 2–4 weeks at five salinities (35, 50, 100, 150, and 230 psu), and generated long-read isoform sequencing (IsoSeq) data to construct a high-quality transcriptome assembly of A. salina. The patterns of A. salina along the salinity gradient provide evidence for halotolerant and euryhaline adaptations at the genetic level. Results: We confirmed that the activity of sodium/potassium ATPase was up-regulated at the genetic level in high salinity waters. Interestingly, genes related to beta-mannosidase and mannose activities were also up-regulated, suggesting that mannose and mannose derivatives may be accumulated as organic osmolytes. Alternatively, considering that glucose and galactose-related activities were suppressed at high salinities, mannose may be the primary sugar involved in the glycolytic pathway under such conditions. This result further supports the theory that mannose is the main energy source used by A. salina in highly saline environments. The gene expression patterns of A. salina may also be affected by increased thickness of the cuticle, increased numbers of mitochondria, and low dissolved oxygen in high salinity waters. Furthermore, the cellular response of A. salina to acclimation to intermediate salinities depends on the number and type of genes expressed; differential expression patterns are likely to fluctuate at the population level. Conclusions: Our results provide a high-quality transcriptome assembly of the cosmopolitan brine shrimp Artemia salina at five different salinities (35, 50, 100, 150, and 230 psu) for the first time. The gene expression patterns of salt-adapted A. salina display greater osmoregulation process complexity than we thought. Furthermore, A. salina represents a potential model organism to study locally adapted populations at various salinities.