Seasonal changes in gene expression and polymorphism of hsp70 in cultivated oysters (Crassostrea gigas) at extreme temperatures

- 600 bp of the hsp70 gene 3′-end of Crassostrea gigas were sequenced.
- 54.5% of the studied organisms expressed high levels of hsp70 during summer.
- 60 polymorphic sites were found in 21 genotypes.
- No significant correlation was observed between polymorphism and expression level.
- A minimum of 134,000 hsp70 transcripts/50 ng of total RNA is an important phenotypic trait.

The HSP70 proteins are an important element of the response against thermal stress and infectious diseases, and they are highly conserved and ubiquitous. In some species, variations on the hsp70 encoding sequence resulted in intraspecific differential expression, which leads to variations on thermo-tolerance among individuals. This phenomenon has not been described in the Pacific oyster Crassostrea gigas, which is cultivated in Mexico under temperature conditions highly above the optimal for this species. The present study was aimed to identify associations between hsp70 genotypes and their expression levels in C. gigas. By analyzing a 603 bp fragment from the 3′ end of the hsp70 gene, 21 different genotypes with 60 nucleotide polymorphic sites were detected, of which 34 sites were found in heterozygous condition. Although no correlation was found between genotype-expression-season, a minimum expression threshold that should be taken into account as an important feature for a future breeding program is proposed.