| Bay scallop Argopecten irradians, first introduced into China from the USA in 1982, has become one of the most important bivalves cultured in China. However,the industry is confronted with difficulties such as disease outbreak, environmental deterioration and also sudden change in climate. Investigating the immunity and stress response of bay scallop is crucial for managing diseases and developing sustainable scallop culture.It has been proved that phagocytosis is one important immune defense reaction when mollusks are exposed to pathogens and various stress. During the course of phagocytosis, a mass of reactive oxygen species are produced to eliminate invaders. At the same time, they may damage cell components such as lipids, proteins, and nucleic acids. Balancing and maintaining appropriate ROS level and suppressing abnormal cell death are essential for the proper functioning of cells and the survival of mollusks. In present study, 3 antioxidant enzyme genes and programmed cell death 4 gene are cloned and analyzed.Two peroxiredoxin genes, PrxⅤand PrxⅥ, were cloned from hemocytes of bay scallop by homology cloning and rapid amplification of cDNA ends (RACE) PCR. The full-length PrxⅤcDNA consisted of 1689 bp with a 567 bp open reading frame(ORF), encoding 188 amino acids. The protein deduced had a molecular mass of 19.9 kDa and a theoretical isoelectric point of 7.49. It shared 78% identity with Chlamys farreri PrxⅤ, 61% identity with Branchiostoma belcheri tsingtauense PrxⅤ,and shared approximately 50% identity with fish, amphibians and mammals. The genomic length of AiPrxⅤgene was 12575 bp containing 6 exons and 5 introns. The gene structure was closely related to chordates and different from arthropods. AiPrxⅤtranscripts were detected in hepatopancreas, hemocytes, gonad, muscle and gill with highest expression in gill. RT-PCR analysis indicated that level of AiPrxⅤ transcripts increased with sampling time, maintaining at a relative high level then dropped. The full-length PrxⅥcDNA was 1657bp, including a 660bp ORF which encoding 219 amino acids. The protein deduced had a molecular mass of 24.3 kDa and a theoretical isoelectric point of 5.97. PrxⅥwas well conserved, AiPrxⅥdisplayed 64%-71% identity with other mollusks such as Aplysia californica and Haliotis discus discus. Moreover, it shared 62% identity with mammals.In genomic DNA, 10k has been analyzed, leading to the conclusion that the gene was composed of 6 extrons and 5 introns. AiPrxⅥwas constitutively expressed in tissues with higher expression in hepatopancreas and gill. RT-PCR analysis showed that AiPrxⅥreached the highest level at 15 h post-injection with V. anguillarum and then decreased and undulated. In addition, a fusion protein containing AiPrxⅥwas produced in vitro with pET-28 system. Study showed that the fusion protein expressed at 20°C other than 37°C regularly and IPTG content had little impact on the expression.Catalase gene was cloned from gill of bay scallop by RACE with degenerate primer designed according to the sequence homolog with catalase genes from other species. AiCAT consisted of 1912 bp with a 1500 bp open reading frame(ORF), encoding 499 amino acids. The protein deduced had a proximal active site signature FNRERIPERVVHAKGAG, a heme-ligand signature RLLSYSDT and underlined 2 putative N-glycosylation sites. The protein deduced had a molecular mass of 56.6 kDa and a theoretical isoelectric point of 6.90. It shared up to 68% identity with corresponding catalase in mammals. The gene was 5356bp, including 10 extrons and 9 introns, and intron9 lied in 3'UTR behind terminal codon TAG. AiCAT was expressed in all sampled tissues with higher level in hepatopancreas and gill. Transcripts in hemocytes decreased first, then reached the hightest at 23h and gradual recovered to nomal level.Programmed cell death 4 gene in bay scallop consisted of 1839bp, containing a 1371bp ORF which encoding 456 amino acids. AiPDCD4 was predicted to be 50.9 kDa with a theoretical isoelectric point of 5.2. It had putative nuclear localisation sites and 2 conserved MA3 domains which were involved in protein-protein interactions.
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