The identification and expression pattern analysis of carbonic anhydrase gene family in marine medaka (Oryzias melastigma) under low salinity environment

Salinity difference is a significant characteristic that distinguishes marine and terrestrial aquatic ecosystems. The carbonic anhydrase (CA) plays an important role in responding to the salinity changes in organisms, including regulating ion transport, osmotic balance, and internal environmental homeostasis. However, there is little research on the multiple ca gene family members under salinity stress. Therefore, we analyzed and researched the ca gene family members under different salinity conditions (0 ‰ and 30 ‰) in a euryhaline fish of marine medaka (Oryzias melastigma). In this study, we have screened and identified 18 members of the family in its genome, which are scattered across 10 chromosomes. Although some members had multiple copies, for example, ca16 with 3 copies, there was no homologous pair among the ca genes. These proteins were localized in different cellular compartments (cytoplasm, membrane, mitochondrion, extracellular space, and nucleus) and exhibited α helices, β sheets, and loops, with all containing at least one CA catalytic domain. According to the results of transcriptome and qPCR, we concluded that CA1, CA5A, CA12, CAR12, and CAHZA may respond to low salinity stress. Furthermore, RPF2 may be an important interacting protein with these CA proteins. Our results provide a molecular basis for the salinity domestication of fishes.