Stress response to low temperature: Transcriptomic characterization in Crassostrea sikamea x Crassostrea angulata hybrids

Hybridization breeding is deemed to be an effective countermeasure in coping with the genetic decline among marine culture species. Hybrids of Crassostrea angulata male x Crassostrea sikamea female have been shown to express heterosis in nutritive com- ponents and tolerance to hypotonic environments. As intertidal zone organisms, they also experience fluctuations in water temperature. To better understand the cellular and molecular processes of this hybrid species under cold stress, we analyzed the transcriptional response of hybrids after 24 hr of exposure to a low temperature of 12 degrees C. A total of 765 differentially expressed genes were obtained, 493 of which were up-regulated and 272 were down-regulated. Compared to the controls treated at 25 degrees C, energy and amino acid metabolism, protein synthesis, transport and degradation of the hybrids were suppressed. Additionally multiple biochemical and physiological-related proteins and processes were affected to help organisms survive including integrin-linked kinase (part of the PPAR signalling pathway), phenylalanine hydroxylase, GTP binding protein, heat shock proteins and immunity related signalling pathways. Our results provide a relatively comprehensive view about cold tolerance in this oyster hybrid species, offering a more solid theoretical foundation for further study and possible expansion of hybrid cultivation.