Two superoxide dismutase (SOD) with different subcellular localizations involved in innate immunity in Crassostrea hongkongensis

SODs are ubiquitous metalloenzymes that can scavenge superoxides in response to various stresses. In the present study, full-length cDNAs of two SOD genes were isolated from Crassostrea hongkongensis (designated ChMnSOD and ChCuZnSOD). The cDNAs are 997 and 918 bp in length with ORFs of 675 and 468 bp (encoding 225 and 156 amino acids), respectively. Sequence analysis revealed a conserved Sod_Fe domain in ChMnSOD, and a Sod_Cu_Zn domain in ChCuZnSOD. Subcellular localization of ChMnSOD is mitochondrial while intracellular expression of ChCuZnSOD is detected. Although their expression overlaps in a wide range of tissues, ChMnSOD mRNA expression is high in gonad while ChCuZnSOD’s is strong in adductor muscle. After infection by Vibrio alginolyticus, ChMnSOD mRNA was up-regulated 5 fold (p < 0.05) at 4 h, but returned to normal level 6 h post-infection. The expression of ChCuZnSOD gene showed a slight delay to the infection challenge and was elevated roughly 4 fold after 8 h (p < 0.05), returning to normal at 12 h post-infection. The elevated transcript levels of the two SOD genes in response to V. alginolyticus infection highlights their important functions in eliminating toxic reactive oxygen species (ROS) and protecting organisms from bacterial invasion in C. hongkongensis.