Genome‐wide identification and expression analysis of mitogen‐activated protein kinase (MAPK) genes in response to salinity stress in channel catfish (Ictalurus punctatus)

The mitogen‐activated protein kinase (MAPK) gene family has been systematically described in several fish species, but less so in channel catfish (Ictalurus punctatus), which is an important global aquaculture species. In this study, 16 MAPK genes were identified in the channel catfish genome and classified into three subfamilies based on phylogenetic analysis, including six extracellular signal regulated kinase (ERK) genes, six p38‐MAPK genes and four C‐Jun N‐terminal kinase (JNK) genes. All MAPK genes were distributed unevenly across 10 chromosomes, of which three (IpMAPK8, IpMAPK12 and IpMAPK14) underwent teleost‐specific whole genome duplication during evolution. Gene expression profiles in channel catfish during salinity stress were analysed using transcriptome sequencing and qRT‐PCR (quantitative reverse transcription PCR). Results from reads per kilobase million (RPKM) analysis showed IpMAPK13, IpMAPK14a and IpMAPK14b genes were differentially expressed when compared with other genes between treatment and control groups. Furthermore, three of these genes were validated by qRT‐PCR, of which IpMAPK14a expression levels were significantly upregulated in treatment groups (high and low salinity) when compared with the control group, with the highest expression levels in the low salinity group (P