The heat shock protein 20 gene family in large yellow croaker (Larimichthys crocea): Identification, phylogenetic relationships, expression analyses.

• 11 hsp20 genes were identified in large yellow croaker. • Hsp20 genes were evolutionarily-constrained among fishes. • Hsp20 genes functions in environmental adaptation of fishes. Large yellow croaker (Larimichthys crocea) is an economically important fish in China, but its aquaculture industry has been threatened by both biotic and abiotic stressors such as hypoxia and pathogens. In the current study, hsp20 genes were identified and analyzed systematically for the first time from the genome of large yellow croaker, and their roles in hypoxia response and Aeromonas hydrophila, Pseudomonas plecoglossicida infection were investigated. Herein, 11 hsp20 genes were identified and annotated, phylogenetic analysis and selection pressure analysis showed that the hsp20 genes were evolutionarily-constrained and their function was conserved among fishes. Besides, we observed the expression patterns of the hsp20 genes under hypoxia and two pathogens' stress. In brief, seven, four, seven genes responded to hypoxia stress, A. hydrophila infection and P. plecoglossicida challenge, respectively, which indicated that they were involved in hypoxia and disease responses. Furthermore, pathogen- and time-specific pattern was observed after A. hydrophila and P. plecoglossicida infection whereas tissue-specific pattern was observed after hypoxia exposure, revealing that hsp20 genes showed differential functions in response to hypoxia and immune stress. Taken together, these results provided preliminary information for future analysis of the roles of hsp20 genes in both biotic and abiotic stress response in fish. [ABSTRACT FROM AUTHOR]