Effect of carotenoids on expression of heat shock protein 22 gene in pearl oyster (Pinctada fucata)

We obtained the full-length cDNA sequence of heat shock protein 22 gene (GenBank accession No.: MG013985, named PfHSP22) from pearl oyster (Pinctada fucata). The full length of PfHSP22 cDNA was 2 187 bp, including a 699 bp ORF (open reading frame) which encoded 232 amino acid residues. PfHSP22 was predicted to contain the "α-crystal domain" (ACD), a typical domain of the small heat shock protein family. The amino acid sequence alignment results show that PfHSP22 had the highest similarity (54%) with HSP22 of Sinonovacula constricta. The phylogenetic analysis shows that PfHSP22 was closely related with molluscs. The qRT-PCR (quantitative real-time PCR) analysis reveals that PfHSP22 gene was expressed in various tissues of orange adductor muscle individuals with high carotenoids content and white adductor muscle individuals with low carotenoids content. The highest expression of PfHSP22 was observed in foot, and the expression of PfHSP22 in orange group was significantly higher than that in white group at normal temperature (P<0.05). It is indicated that the level of carotenoids might affect the basic expression of PfHSP22 gene. During the high temperature stress process, the expression of PfHSP22 in each tissue generally showed a downward trend in the first 3 h, and then showed a complex change of increase or decrease. There were several tissues whose time for PfHSP22 gene expression to rise significantly was later in orange group than in white group, which might be caused by the difference in the carotenoid content.