Investigating the differences in metabolism, and the unfolded protein and apoptosis gene responses in two strains of the Pacific white shrimp, Penaeus vannamei Boone, 1931 (Decapoda, Penaeoidea) under ammonia stress

Ammonia is one of the major environmental pollutants in the aquatic system and poses a great threat to shrimp. In this study, we compared the differences in metabolic enzymes and the mRNA expression of unfolded protein response (UPR)-related genes between the ammonia-resistant (LV-AT) and ammonia-sensitive (LV-AS) strains of Penaeus vannamei, aiming to investigate the different tolerance mechanisms of the two extreme strains underlying ammonia stress. The results showed that elevated ammonia concentrations mainly increased glutamine synthetase (GS) content while inhibiting transglutaminase (TG) content in the muscle of both strains and the contents were significantly higher in LV-AT than in LV-AS after 48 h of ammonia stress (). As a protective or adaptive strategy, the expression of the UPR related genes, including activating transcription factors ATF6, ATF4, and the spliced form of X box binding protein 1 (XBP1) were, respectively, either significantly induced, or inhibited () after ammonia stress. The mRNA expressions of the GRP78 (Bip) gene and the apoptosis gene (caspase 3) are then activated. In hepatopancreas and gills, the associated gene expressions gradually increase in LV-AT, while several related genes in LV-AS were first induced and then gradually inhibited. The expressions of key genes (GRP78, ATF6, XBP1 and ATF4) were significantly higher in LV-AT than that in LV-AS after 48 h of ammonia stress (). These results indicate that some enzymes involved in ammonia metabolism and UPR protection genes tended to be highly expressed in LV-AT. Hence, we speculate that LV-AT has a higher ammonia excretion capacity and a more effective adaptive mechanism after ammonia stress. The experimental results will help to further understand the stress response of P. vannamei to ammonia and provide a new perspective for the underlying molecular mechanism of the ammonia adaptation strategy of at least some strains of P. vannamei.