Identification of mapk genes, and their expression profiles in response to low salinity stress, in cobia (Rachycentron canadum)

Mitogen-activated protein kinases (MAPKs) are a class of protein kinases that regulate various physiological processes, and play a crucial role in maintaining the osmotic equilibrium of fish. The objective of this study was to identify and characterize the mapk family genes in cobia (Rachycentron canadum) and examine their expression profiles under different low salinity stress regimes (acute: from 30‰ to 10‰ in 1 h, sub-chronic: from 30‰ to 10‰ over 4 d). A total of 12 cobia mapk genes (Rcmapks) were identified and cloned, including six erk subfamily genes (Rcmapk1/3/4/6/7/15), three jnk subfamily genes (Rcmapk8/9/10) and three p38 mapk subfamily genes (Rcmapk 11/13/14). Domain analysis indicated that the RcMAPKs possessed the typical domains including S_TKc and PKc_like domain. Phylogenetic analysis revealed that the Rcmapks were most closely related to those of the turbot (Scophthalmus maximus). The tissue distribution of mapk genes in adult cobia and the expression patterns of Rcmapks under different low salinity stress regimes were investigated using quantitative real-time PCR (qRT-PCR). The results revealed that Rcmapk3/9/10/11/13/14 exhibited a relatively broad expression distribution across 14 different tissues. For all these genes the highest expression level was in the brain, except for Rcmapk14 (highly expressed in the stomach, gill, and skin). The genes Rcmapk1/6/15 showed significantly higher expression in the testis. Under acute low salinity stress, expression of Rcmapk1/3/6/7/9/11/13/14 was significantly altered in the gill, intestine, and trunk kidney, however, the aforementioned genes exhibited very different expression patterns among the three tissues. In the gill, most of the genes from the erk (Rcmapk3/6/7) and p38 mapk subfamily (Rcmapk11/13/14) were significantly up-regulated at almost all the time points (P < 0.05); Similarly, the expression of Rcmapk3/9/11/13/14 genes were significantly increased in the trunk kidney; while in the intestine, most of the altered genes (Rcmapk6/7/9/11/13/14) were significantly down-regulated at 1 h. Following the sub-chronic low salinity stress, expression of Rcmapk1/3/6/7/9/11/13/14 genes were significantly altered in all three tissues. These findings provide important reference data for elucidating the roles of cobia mapk family genes in response to low salinity stress.