RNAi based transcriptome suggests genes potentially regulated by HSF1 in the Pacific oyster Crassostrea gigas under thermal stress

Background The Pacific oyster Crassostrea gigas is an important fishery resource that is sensitive to temperature fluctuations. Thus, it has evolved a protection mechanism against heat stress by increasing the expression of the gene coding for heat shock protein (HSP) 70 under elevated temperatures. In other animals, heat shock response is a transcriptional response driven by the heat shock transcription factor 1 (HSF1) and thermal stress can trigger HSP70 expression to protect the organism via HSF1. However, the regulatory relationship between HSF1 and HSP remains unclear in Pacific oyster. Therefore, in the present study, we examined the transcriptomic response of several to thermal stress following HSF1 interference. Results We identified 150 genes responsive to heat shock including seven HSP genes, six of which belonging to the group of 17 HSP genes enriched in response to heat shock, according to weighted gene co-expression network analysis (WGCNA). The other gene was enriched in the module correlated with HSF1 interference. In addition, we found 48 and 47 genes that were upregulated and downregulated by HSF1 in response to heat shock, respectively. In the upregulated genes, we identified one HSP70 potentially regulated by HSF1 in response to heat shock. Furthermore, based on differentially expressed genes and WGCNA analyses, we found that the hypoxia signaling pathway was enriched under heat shock conditions. Five genes were then selected to detect dynamic changes through time. The results suggested that gene expression was correlated with HSF1 expression. The regulation of HSP70 by HSF1 was preliminarily confirmed by binding site predictions and by a dual luciferase assay. Conclusions Our results revealed that the expression of HSP70 and HSP20 was initially triggered after 2 h of heat shock, and one of the HSP70 genes was potentially regulated by HSF1. From these results, it is evident that not all heat-inducible genes were triggered simultaneously in response to heat shock stress. Overall, the results revealed a possible HSF1-HSP regulatory relationship in Pacific oyster, providing valuable information on the mechanisms of thermal tolerance in this commercially important oyster.