Contraction of Heat Shock Protein 70 Genes Uncovers Heat Adaptability of Ostrea denselamellosa

The milin oyster Ostrea denselamellosa is a live-bearing species with a sharp decline in the natural population. Unlike other oysters, O. denselamellosa lives in the subtidal zone and its adaptability to heat, salinity, etc. is different from most other oysters. Heat shock proteins 70 (HSP70) are a family of conserved ubiquitously expressed heat shock proteins which are produced in response to stressful conditions, especially heat. In this study, we identified Hsp70 genes through bioinformatic analysis in five species of oyster. Among them, O. denselamellosa holds the fewest number of Hsp70 genes, which may be one of the reasons why O. denselamellosa cannot tolerate high temperatures. The conserved motifs and gene structures of Hsp70B2 sub-family and other types of Hsp70 in O. denselamellosa were different from that of Hspa12 sub-family, which may be due to performing necessary multiple physiological functions. Transcription profile analysis for Hsp70 genes of O. denselamellosa indicated that gills play an important role in responding to multiple external challenges. In addition, synteny analysis of Hsp70 genes among O. denselamellosa, O. edulis and Crassostrea ariakensis showed that Hsp70 genes in genus of Ostrea genome might have evolved from a common ancestor with genus of Crassostrea. In short, our results lay the foundation for further investigation of the evolution of O. denselamellosa Hsp70 genes and heat adaptability.