Physiological Genomic Response to Variable Salinity Environments by the Tiger Shrimp (Penaeus monodon)

Abstract

Osmoregulation is considered as the principal mechanism for survival and adaptation to different salinity conditions. The present study was conducted to evaluate mRNA expression levels of six osmoregulatory (two hemolymph regulatory and four ion regulatory) genes that play important role in osmoregulation in a penaeid shrimp, Penaeus monodon, exposed to three different experimental salinities (0‰, 10‰ and 20‰) for a period of 30 days, using an RT-qPCR approach. Relative mRNA expression patterns revealed comparatively higher expression levels of Crustacean Hyper-glycaemic Hormone (CHH) and Na⁺/K⁺/2Cl⁻ Cotransporter (NKCC) genes at raised salinities (10‰ and 20‰). At 0‰ vs 20‰, expression levels of these two genes were significantly higher (p < 0.05) and showed 1.5–2 fold and 2–3 fold higher (higher in 10‰ than 0‰) expression levels for CHH and NKCC, respectively. Significantly different expression levels were observed for these two genes among salinities (p < 0.05) throughout the experiment. Significantly higher expression levels (p < 0.05) were observed at 0‰ for the Diuretic Hormone (DH), Na⁺/K⁺-ATPase (NKA), Na⁺/H⁺ exchanger (NHE) and V-type H⁺-ATPase (VTA) genes over 10‰ and 20‰ throughout the experimental period. But initially higher expression levels of VTA were found at 0‰ up to 24 h and then dropped towards the level at 10 day. The ion regulatory gene V-type H⁺-ATPase (VTA) and Na⁺/H⁺ exchanger (NHE) showed very high expression levels at reduced salinity (0‰). At 0‰ vs 20‰, expression levels of these two genes were significantly higher (p < 0.05) and showed 4–5 fold and 3–5 fold higher (higher in 0‰ than 20‰) expression levels for VTA and NHE, respectively. In general, CHH, NKA, NHE and VTA were up-regulated in freshwater while DH and NKCC were up-regulated under raised salinities. Results of this study revealed that the genes examined here played key roles in adaptive responses to variable environmental salinity conditions broadly in aquatic crustaceans.