Transcriptomic and BSA analysis provide insight into the metabolic regulation mechanism in filefish Thamnaconus septentrionalis under low salt stress

Abstract

This study provided insights into the adaption of greenfin horse-faced filefish Thamnaconus septentrionalis toward low-salinity conditions. A combination of antioxidant enzyme activity, transcriptome technology, and BSA sequencing analysis was employed to investigate the osmotic balance, oxidative stress, and immune response in this species. The salinity levels were controlled at 21 PSU (control group), with two treatment groups, Group C (salinity reduction at a rate of 1 PSU per day) and Group A (salinity reduction at a rate of 6 PSU per day), respectively. As a result, with the decrease of salinity, the activities of SOD, CAT, and GSH-PX, as well as the content of MDA, showed varying degrees of increased. The findings indicated that a reduction in salinity can lead to oxidative damage induced by reactive oxygen species (ROS), which in turn activated the activity of antioxidant enzymes in fish to maintain the balance of ROS metabolism. When the salinity was reduced to 15 PSU, there were more DEGs in Groups A and Group C. The KEGG enrichment pathway showed that DEGs were most significantly enriched in the arachidonic acid metabolism, IL-17 signaling, glycine, serine, threonine metabolism, and glutathione metabolism pathways. The BSA sequencing results showed that single nucleotide polymorphisms (SNP) and insertions and deletions (Indel) were co-located on LG08, LG09, LG14, LG15, and LG19 chromosomes. A combined analysis revealed the identification of 52 SNP loci and 22 candidate genes on chromosomes associated with low-salt tolerance trait, which were significantly enriched in tight cell junctions, cytokine receptor interaction pathways, and signal transduction pathways. Upon conducting a joint analysis with the transcriptome, there were five genes, namely CLDN20, IFI44L, MISP, TRIM25, and TSPAN33, that demonstrated significant expression within the transcriptome-filtered DEGs. This study contributes significantly to advancing the understanding of osmotic regulation and immune response mechanism in T. septentrionalis.