Characterisation, evolution and expression analysis of heat shock protein 20 genes from Japanese flounder (Paralichthys olivaceus) in response to Edwardsiella tarda infection

Abstract Japanese flounder (Paralichthys olivaceus) is an economically important flatfish endemic to Asia that faces natural challenges, such as heat shock and bacterial infection. Here, we investigated whether heat shock protein 20 (hsp20) in Japanese flounder played a role in immune reactions against Edwardsiella tarda. Hsp20 is ubiquitously produced by cells in the stress response; it not only functions as a chaperone and housekeeping protein but also participates in the immune response during infection. In this study, we identified and annotated 13 hsp20 genes using bioinformatic methods in Japanese flounder. Phylogenetic and selection pressure analysis showed that the hsp20 genes were evolutionarily-constrained and their function was conserved. Hsp20 genes are also involved in the embryogenesis and act as the sentinel role in an unchallenged organism. Moreover, the regulated expression patterns of hsp20 genes after E. tarda infection were examined for the first time in Japanese flounder. Eleven out of 13 genes were differentially expressed after bacterial challenge, which indicated that they may be involved in disease response genes or as disease defence against pathogens. These results provide valuable information for clarifying the evolutionary relationship of the hsp20 genes, and early insights into the immune functions of hsp20 genes in Japanese flounder.