Comparative transcriptomic analyses reveal differences in the responses of diploid and triploid Pacific oysters (Crassostrea gigas) to thermal stress

Triploid oysters often have higher growth rates and survival rates than diploid oysters. However, some studies have observed the opposite patterns. Triploid oysters have also been observed to show reduced resistance to stress and disease compared with diploid oysters. We compared the transcriptional patterns of diploid and triploid Pacific Oysters (Crassostrea gigas) in response to acute and prolonged thermal stress. The survival rate of triploid C. gigas was lower than that of diploid oysters after prolonged heat stress at 28 ?C. A total of 779 and 396 differentially expressed genes (DEGs) were detected in diploid and triploid oysters exposed to acute heat stress, respectively, and the number of DEGs was 418 in diploids and 483 in triploids after prolonged heat stress. Functional enrichment analysis revealed that the DEGs were significantly enriched in protein processing in the endoplasmic reticulum pathway, NF-kappa B signaling pathway, NOD-like receptor signaling pathway, and TNF signaling pathway in both diploid and triploid C. gigas under heat stress. Genes encoding translation initiation factors, including MKNK1, eIF4G3, eIF2a kinase 1, and eIF2a kinase 3, were differentially expressed under acute heat stress in diploid oysters. The number of differentially expressed HSP and IAP genes was greater in diploids than in triploids under acute heat stress, and the expression levels of most of these HSP and IAP genes were higher in diploid oysters than in triploid oysters. Overall, our findings revealed differences in the response of diploid and triploid C. gigas to thermal stress. Triploid C. gigas might be less capable of rapidly modifying the inflammatory response and apoptosis in response to heat stress compared with diploid C. gigas. Different genetic lines of diploid and tetraploid oysters should be used to produce triploid oysters with increased stress resistance.