Effect of Low Salinity Stress on Expression Profiles of the Mapk Family Genes in Cobia (Rachycentron Canadum)

Abstract

Mitogen-activated protein kinases (MAPKs) are a class of protein kinases that regulate various physiological processes, and play a crucial role in maintaining 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. As a result, a total of 12 cobia mapk genes (Rcmapks) were identified and cloned, including six erk (Rcmapk1/3/4/6/7/15), three jnk (Rcmapk8/9/10) and three p38 mapk (Rcmapk 11/13/14) subfamily genes. 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). Tissue distribution of mapk genes in adult cobia was 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, with the highest expression level in the brain only excepting for Rcmapk14 (highly expressed in the stomach, gill and skin); Rcmapk1/6/15 showed a significantly higher expression in the testis than in the other tissues (P < 0.05). The expression pattern of Rcmapks under different low salinity stress were analyzed by qRT-PCR. Under acute low salinity stress, expression of Rcmapk1/3/6/7/9/11/13/14 were significantly altered in the gill, intestine and body kidney, however, the aforementioned genes exhibited very different expression patterns among the three tissues. As for the gill, most of the genes from erk (Rcmapk3/6/7) and p38 mapk (Rcmapk11/13/14) subfamily were significantly up-regulated at almost all the time points (P < 0.05); similarly, the expression of Rcmapk3/9/11/13/14 were significantly increased in the body kidney; while in the intestine, most of the altered genes (Rcmapk6/7/9/11/13/14) were significantly down-regulated at 1h. Following the chronic low salinity stress, expression of Rcmapk1/3/6/7/9/11/13/14 were significantly altered in the aforementioned three tissues, the regulated expression of all these genes could detected at 7d in the gill, however, expression changes of the Rcmapks in intestine and body kidney mostly happened at 14 and 21 d. These findings would provide important reference data for elucidating the roles of mapk family genes in the response of cobia to low salinity stress.

Keywords: mapk, Rachycentron canadum, low salinity, gene expression