Transcriptome Analysis Reveals the Key Genes and Pathways for Growth, Ion Transport, and Oxidative Stress in Post-Larval Black Tiger Shrimp (Penaeus monodon) Under Acute Low Salt Stress

As an abiotic stress factor, salinity significantly affects the physiological activities of crustaceans. In this study, transcriptome sequencing was used to evaluate the mechanism of ion transport and the physiological response of black tiger shrimp (Penaeus monodon) under low salt stress. Four hundred post larval (PL) stage P. monodon were distributed in eight experimental tanks and exposed to 3 or 5 ppt salt concentrations for 96 h. Low salinity significantly reduced the survival rate of shrimp but simultaneously activated the activity of ion transporter enzymes Na+/K+-ATPase (NKA) and Ca2+/Mg2+-ATPase), the expression of NKA, galectin 10, and cytochrompe c peroxidase genes, and the activity and expression of antioxidant-related genes (superoxide dismutase, catalase, heat shock protein 60). Low salt stress activated the urea cycle but significantly inhibited glutathione metabolization-related indicators (glutamate dehydrogenase, glutaminase, glutamic acid). RNA-seq analysis identified 221 differentially expressed genes (78 up-regulated and 143 down-regulated). Quantitative real-time PCR and RNA-seq results of 11 of them were consistent, illustrating the validity of the transcriptomic predictions. Gene set enrichment analysis results showed that calcium ion transmembrane transport, calmodulin binding, the stress-activated protein kinase signaling cascade, and regulation of the cytosolic calcium ion concentration process were significantly enriched. These results showed that low salt stress activated the calcium-dominated ion transport pathway and promoted molting growth of P. monodon. They also indicate that there is potential for larval rearing shrimp under low salt conditions.