Two classes of glutathione S-transferase genes with different response profiles to bacterial challenge in Venerupis philippinarum

Glutathione S-transferase (GST) genes from marine copepods Acartia tonsa: cDNA cloning and mRNA expression in response to 1,2-dimethylnaphthalene

The calanoid copepod, Acartia tonsa, is relatively sensitive to marine pollution. Glutathione S-transferase (GST) multifunctional enzyme, as a biomarker, play an important role in detoxification metabolism of exogenous substances. In the present study, GST-theta and GST-mu class homology genes (designated as AtGSTT1 and AtGSTM2) were identified and characterized from A. tonsa. The coding sequence of AtGSTT1 comprised 726 bp and encoded a putative protein of 241 amino acid residues. AtGSTM2 contained an open reading frame of 678 bp that encoded a putative 227 amino acid polypeptide. Both proteins contained a conserved GST-N domain and a GST-C domain. Structural analysis revealed the characteristic N-terminal G-site. Three-dimensional structure analysis showed that AtGSTT1 and AtGSTM2 have two typical domains of GST family: The βαβαββα topology structure at the N- terminus and the superhelical structure at the C- terminus. Subsequently, the expression levels of the two GST genes were detected in A. tonsa using real-time quantitative PCR after exposure to 1,2-dimethylnaphthalene (C2-NAPH) at different concentrations (0.574, 5.736 and 57.358 μg/L) for 24, 48, 72, and 96 h. AtGSTT1 mRNA expression was significantly up-regulated in a time-dependent manner and the highest mRNA expression occurred at 5.736 μg/L C2-NAPH exposure for 96 h. AtGSTM2 mRNA expression peaked at 72 h in 0.574 μg/L and 5.736 μg/L dose groups. The expression level of AtGSTM2 showed an increasing trend in a time-dependent manner at 57.358 μg/L of C2-NAPH. These results suggested that GST genes may play an important role in protecting A. tonsa from C2-NAPH pollution, and provide a theoretical basis for further study on the molecular mechanism of polycyclic aromatic hydrocarbon (PAHs) pollution on zooplankton.

Molecular and expression characterization of Toll-like receptor family genes from the Anadara sativa (Bivalvia, Arcidae) transcriptome

Innate immunity plays an important role in invertebrates because it provides the first line of protection by recognizing invading microbial pathogens and then activating downstream signaling pathways. However, until now, increasing reports of clam diseases did not include those of Anadara sativa, which are widely distributed and economically important maritime clams. In the present study, transcriptome libraries of untreated (termed H) and Vibrio anguillarum-challenged (termed HV) A. sativa hepatopancreases were constructed and sequenced using the Illumina HiSeq4000 platform. In total, we obtained 78,012,510 and 84,937,516 clean reads from 80,006,030 to 86,871,742 raw data reads, respectively, assembled by different software programs. Furthermore, 150,274 unigenes were generated from 196,003 transcripts, with an N50 length of 1088 bp, and then annotated with the SwissProt, NR, NT, PFAM, KO, GO, KOG and KEGG databases. Moreover, 3982 differentially expressed unigenes (H vs HV) were determined, with 3583 upregulated and 399 downregulated genes. Among these differentially expressed unigenes, 207 unigenes were found using KEGG annotation in 16 immune-related signaling pathways, such as Toll-like receptor (TLR), NOD-like receptor (NLR), and RIG-I-like receptor (RLR) signaling pathways. Finally, we selected 11 full-length TLRs and classified them into 3 groups, namely, one V-TLR, four Ls-TLR and six sP-TLR; furthermore, we validated the increased expression patterns of the 11 TLRs in response to LPS injection. In summary, these results revealed multiple findings on potential immune-related genes, such as the differential expression analysis and annotation based on the A. sativa transcriptome in response to V. anguillarum stimulation, and explored the molecular and expression characterization of A. sativa TLRs, which provide new insights into the innate immune responses and defense mechanisms in shellfish.

Molecular characterization of kappa class glutathione S-transferase from the disk abalone (Haliotis discus discus) and changes in expression following immune and stress challenges

Glutathione S-transferase (GST; EC 2.5.1.18) isoenzymes represent a complex group of proteins that are involved in phase II detoxification in several organisms. In this study, GST kappa (GSTκ) from the disk abalone (Haliotis discus discus; AbGSTκ) was characterized at both the transcriptional and functional levels to determine its potential capacity to perform as a detoxification agent under conditions of different stress. The predicted AbGSTκ protein consists of 227 amino acids, with a predicted molecular weight of 25.6 kDa and a theoretical isoelectric point (pI) of 7.78. In silico analysis reveals that AbGSTκ is a disulfide bond formation protein A (DsbA), consisting of a thioredoxin domain, GSH binding sites (G-sites), and a catalytic residue. In contrast, no hydrophobic ligand binding site (H-site), or signal peptides, were detected. AbGSTκ showed the highest sequence identity with the orthologue from pufferfish (Takifugu obscurus) (60.0%). In a phylogenetic tree, AbGSTκ clustered closely together with other fish GSTκs, and was evolutionarily distanced from other cytosolic GSTs. The predicted three-dimensional structure clearly demonstrates that the dimer adopts a butterfly-like shape. A tissue distribution analysis revealed that GSTκ was highly expressed in the digestive tract, suggesting it has detoxification ability. Depending on the tissue and time, AbGSTκ showed different expression patterns, and levels of expression, following challenge of the abalone with immune stimulants. Enzyme kinetics of the purified recombinant proteins demonstrated its conjugating ability using 1-Chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH) as substrates, and suggested it has a low affinity for both substrates. The optimum temperature and pH for the rAbGSTκ GSH: CDNB conjugating activity were found to be 35 °C and pH 8, respectively indicating that the abalone is well adapted to a wide range of environmental conditions. Cibacron blue (100 μM) was capable of completely inhibiting rAbGSTκ (100%) with an IC₅₀ (half maximal inhibitory concentration) of 0.05 μM. A disk diffusion assay revealed that rAbGSTκ could significantly protect cells from H₂O₂, CdCl_2, and ZnCl₂. Altogether, this current study suggests that AbGSTκ is involved in detoxification and immunological host defense mechanisms and allows abalones to overcome stresses in order for them to have an increased chance of survival.

Molecular cloning, biochemical characterization, and expression analysis of two glutathione S-transferase paralogs from the big-belly seahorse (Hippocampus abdominalis)

Glutathione S-transferases (GSTs, EC 2.5.1.18) are important Phase II detoxifying enzymes that catalyze hydrophobic, electrophilic xenobiotic substance with the conjugation of reduced glutathione (GSH). In this study, GSTμ and GSTρ paralogs of GST in the big belly seahorse (Hippocampus abdominalis; HaGSTρ, HaGSTμ) were biochemically, molecularly, functionally characterized to determine their detoxification range and protective capacities upon different pathogenic stresses. HaGSTρ and HaGSTμ are composed of coding sequences of 681bp and 654bp, which encode proteins 225 and 217 amino acids, with predicted molecular masses of 26.06kDa and 25.74kDa respectively. Sequence analysis revealed that both HaGSTs comprise the characteristic GSH-binding site in the thioredoxin-like N-terminal domain and substrate binding site in the C-terminal domain. The recombinant HaGSTρ and HaGSTμ proteins catalyzed the model GST substrate 1-chloro-2, 4-dinitrobenzene (CDNB). Enzyme kinetic analysis revealed different K_m and V_max values for each rHaGST, suggesting that they have different conjugation rates. The optimum conditions (pH, temperature) and inhibitory assays of each protein demonstrated different optimal ranges. However, HaGSTμ was highly expressed in the ovary and gill, whereas HaGSTρ was highly expressed in the gill and pouch. mRNA expression of HaGSTρ and HaGSTμ was significantly elevated upon lipopolysaccharide, Poly (I:C), and Edwardsiella tarda challenges in liver and in blood cells as well as with Streptococcus iniae challenge in blood cells. From these collective experimental results, we propose that HaGSTρ and HaGSTμ are effective in detoxifying xenobiotic toxic agents, and importantly, their mRNA expression could be stimulated by immunological stress signals in the aquatic environment.

Transcriptome analysis of Ruditapes philippinarum hepatopancreas provides insights into immune signaling pathways under Vibrio anguillarum infection

The Manila clam, Ruditapes philippinarum, is one of the most economically important aquatic clams that are harvested on a large scale by the mariculture industry in China. However, increasing reports of bacterial pathogenic diseases have had a negative effect on the aquaculture industry of R. philippinarum. In the present study, the two transcriptome libraries of untreated (termed H) and challenged Vibrio anguillarum (termed HV) hepatopancreas were constructed and sequenced from Manila clam using an Illumina-based paired-end sequencing platform. In total, 75,302,886 and 66,578,976 high-quality clean reads were assembled from 101,080,746 and 99,673,538 raw data points from the two transcriptome libraries described above, respectively. Furthermore, 156,116 unigenes were generated from 210,685 transcripts, with an N50 length of 1125 bp, and from the annotated SwissProt, NR, NT, KO, GO, KOG and KEGG databases. Moreover, a total of 4071 differentially expressed unigenes (HV vs H) were detected, including 903 up-regulated and 3168 down-regulated genes. Among these differentially expressed unigenes, 226 unigenes were annotated using KEGG annotation in 16 immune-related signaling pathways, including Toll-like receptor, NF-kappa B, MAPK, NOD-like receptor, RIG-I-like receptor, and the TNF and chemokine signaling pathways. Finally, 20,341 simple sequence repeats (SSRs) and 214,430 potential single nucleotide polymorphisms (SNPs) were detected from the H and HV transcriptome libraries. In conclusion, these studies identified many candidate immune-related genes and signaling pathways and conducted a comparative analysis of the differentially expressed unigenes from Manila clam hepatopancreas in response to V. anguillarum stimulation. These data laid the foundation for studying the innate immune systems and defense mechanisms in R. philippinarum.

Isolation and characterization of two glutathione S-transferases from freshwater bivalve Anodonta woodiana: Chronic effects of pentachlorophenol on gene expression profiles

Glutathione S-transferases (GST) play a prominent role in protecting cells against oxidative stress. Our previous study showed that the reactive oxygen species (ROS) generated from pentachlorophenol (PCP) could cause an acute impact on freshwater bivalve Anodonta Woodiana, but its chronic toxicity remain unclear. In order to investigate the chronic effect of PCP, clams A. Woodiana were randomly grouped into PCP treated group in which animals were administrated with 13.9 μg/L concentrations of PCP, and control group those with similar volume dimethyl sulfoxide. In addition, two complete GST sequences were isolated from A. Woodianaa and respectively named AwGST1 and AwGST2. The full-length cDNA of AwGST1 was consisted of a 5' untranslated region (UTR) of 132 bp, a 3' UTR of 80 bp and an open reading frame (ORF) of 609 bp encoding a polypeptide of 203 amino acids. The full-length cDNA of AwGST2 contained a 5' UTR of 57 bp, a 3' UTR of 291 bp and an ORF of 678 bp encoding a polypeptide of 226 amino acids. The constitutive expression levels of AwGST1 and AwGST2 were examined in different tissues including foot, mantle, adductor muscle, heart, hepatopancreas, hemocytes and gill. Administration of PCP could result in a significant increase of AwGST1 and AwGST2 expression in the hepatopancreas, gill and hemocytes. In the hepatopancreas, AwGST1 mRNA levels of PCP treated group increased more than 28.73% at day 1, then 70.37% (P < 0.05) at day 3, reach to 6.64 times (P < 0.01) at day 15 in contrasted with that of control group. AwGST2 increased more 18.18%, 82.88% (P < 0.05) and 2.43 times (P < 0.01) at day 1, 3 and 15, respectively. In the gill, AwGST1 expression showed a significant up-regulation in the PCP treated group during experiment observed compared with that of control group, mRNA level of AwGST2 increased more than 1.44 times (P < 0.05). In addition, expressions of AwGST1 and AwGST2 were significantly induced after PCP treatment in the hemocytes. These results indicated that up-regulations of AwGST1 and AwGST2 expression in bivalve A. woodiana are contribute to against oxidative stress derived from PCP treatment during experiment observed.

Molecular cloning and functional characterization of theta class glutathione S-transferase from Apostichopus japonicus

Glutathione S-transferases (GSTs) are the superfamily of multifunctional detoxification isoenzymes and play crucial roles in innate immunity. In the present study, a theta class GST homology was identified from A. japonicus (designated as AjGST-θ) by RACE approaches. The full-length cDNA of AjGST-θ was of 1013 bp encoded a cytosolic protein of 231 amino acids residues. Structural analysis revealed that AjGST-θ processed the characteristic N-terminal GSH-binding site (G-site) and the C-terminal hydrophobic substrate binding site (H-site). Multiple sequence alignment and phylogenetic analysis together supported that AjGST-θ belonged to a new member of theta class GST protein subfamily. Spatial expression analysis revealed that AjGST-θ was ubiquitously expressed in all examined tissues with the larger magnitude in intestine. The Vibrio splendidus challenge in vivo and LPS stimulation in vitro could both significantly up-regulate the mRNA expression of AjGST-θ when compared with control group. The recombinant protein was expressed in Escherichia coli and the purified AjGST-θ showed high activity with GST substrate. Meantime, disc diffusion assay showed that recombinant AjGST-θ protein could markedly improve bacterial growth under Cumene hydroperoxide exposure. More importantly, the recombinant AjGST-θ could effectively prevent primary coelomocytes apoptosis after LPS exposure. Our present findings suggested that AjGST-θ might play significantly roles in the modulation of immune response and protect cells from pathogens infection in A. japonicus.

In-silico analysis and mRNA modulation of detoxification enzymes GST delta and kappa against various biotic and abiotic oxidative stressors

This study reports the comprehensive comparative information of two different detoxification enzymes such as glutathione S-transferases (GSTs) delta and kappa from freshwater giant prawn Macrobrachium rosenbergii (designated as MrGSTD and MrGSTK) by investigating their in-silico characters and mRNA modulation against various biotic and abiotic oxidative stressors. The physico-chemical properties of these cDNA and their polypeptide structure were analyzed using various bioinformatics program. The analysis indicated the variation in size of the polypeptides, presence or absence of domains and motifs and structure. Homology and phylogenetic analysis revealed that MrGSTD shared maximum identity (83%) with crustaceans GST delta, whereas MrGSTK fell in arthropods GST kappa. It is interesting to note that MrGSTD and MrGSTK shared only 21% identity; it indicated their structural difference. Structural analysis indicated that MrGSTD to be canonical dimer like shape and MrGSTK appeared to be butterfly dimer like shape, in spite of four β-sheets being conserved in both GSTs. Tissue specific gene expression analysis showed that both MrGSTD and MrGSTK are highly expressed in immune organs such as haemocyte and hepatopancreas, respectively. To understand the role of mRNA modulation of MrGSTD and MrGSTK, the prawns were inducted with oxidative stressors such as bacteria (Vibrio harveyi), virus [white spot syndrome virus (WSSV)] and heavy metal, cadmium (Cd). The analysis revealed an interesting fact that both MrGSTD and MrGSTK showed higher (P < 0.05) up-regulation at 48 h post-challenge, except MrGSTD stressed with bacteria, where it showed up-regulation at 24 h post-challenge. Overall, the results suggested that GSTs are diverse in their structure and possibly conferring their potential involvement in immune protection in crustaceans. However, further study is necessary to focus their functional differences at proteomic level.

Molecular cloning and characterization of a sigma-class glutathione S-transferase from the freshwater mussel Hyriopsis cumingii

A full-length cDNA of a sigma-like glutathione S-transferase (GST) was identified from Hyriopsis cumingii (HcGSTS). The deduced amino acid sequence of HcGSTS was found to comprise 203 amino acid residues and to contain the distinct highly conserved glutathione binding site of N-terminal and the relatively diverse substrate binding site of C-terminal. Alignment analysis and phylogenetic relationship suggested that the HcGSTS is a sigma-class GST. The mRNA of HcGSTS was constitutively expressed in all tested tissues, the strongest expression being in the hepatopancreas. The mRNA expression of HcGSTS was significantly up-regulated (P < 0.05) in all assessed tissues after stimulation of the mussels with peptidoglycan (PGN) and LPS, the only exception being when the gills were challenged with PGN. The expression of HcGSTS mRNA in kidney and foot was also significantly up-regulated (P < 0.05) by microcystin-LR. Recombinant HcGSTS exhibited high activity towards the substrate 1-chloro-2,4-dinitrobenzene. The optimal pH was 8.0 and temperature 35 °C.

Proteomic identification of differentially expressed proteins in sea cucumber Apostichopus japonicus coelomocytes after Vibrio splendidus infection

Skin ulceration syndrome (SUS) was the main limitation in the development of Apostichopus japonicus culture industries. To better understand how Vibrio splendidus modulates SUS outbreak, the immune response of A. japonicus coelomocytes after the pathogen challenge were investigated through comparative proteomics approach, and differentially expressed proteins were screened and characterized in the present study. A total of 40 protein spots representing 30 entries were identified at 24, 72 and 96 h post-infection. Of these proteins, 32 were up-regulated and 8 were down-regulated in the V. splendidus challenged samples compared to those of control. These differentially expressed proteins were mainly classified into four categories by GO analysis, in which approximate 33% of proteins showed to be related to immunity response. The mRNA expression levels of 6 differentially expressed proteins were further validated by qRT-PCR. Similar protein-mRNA-level expression patterns were detected in genes of phospholipase (spot 4), G protein (spot 20), annexin (spot 30) and filamin (spot 31). Whilst the levels of ficolin (spot 12) and calumenin (spot 14) transcripts were not corresponded with those of their translation products. These data provide a new insight to understand the molecular immune mechanism of sea cucumber responsive towards pathogen infection.

A mu class glutathione S-transferase from Manila clam Ruditapes philippinarum (RpGSTμ): cloning, mRNA expression, and conjugation assays

Glutathione S-transferases (GSTs) are enzymes that catalyze xenobiotic metabolism in the phase II detoxification process. GSTs have a potential for use as indicators or biomarkers to assess the presence of organic and inorganic contaminants in aquatic environments. In this study, a full-length cDNA of a mu (μ) class GST (RpGSTμ) was identified from Manila clam (Ruditapes philippinarum) and biochemically characterized. The 1356 bp of the cDNA included an open reading frame of 651 bp encoding a polypeptide of 217 amino acid residues with a molecular mass of 25.04 kDa and an estimated pI of 6.34. Sequence analysis revealed that the RpGSTμ possessed several characteristic features of μ class GSTs, such as a thioredoxin-like N-terminal domain containing binding sites for glutathione (GSH), a C-terminal domain containing substrate binding sites, and a μ loop. The recombinant RpGSTμ (rRpGSTμ) protein exhibited GSH-conjugating catalytic activity towards several substrates, and significantly strong activity was detected against 4-nitrophenethyl bromide (5.77 ± 0.55) and 1-chloro-2,4-dinitrobenzene (CDNB, 3.19 ± 0.05). Kinetic analysis as a function of GSH and CDNB concentrations revealed relatively low Km values of 1.03 ± 0.46 mM and 0.56 ± 0.20 mM, respectively, thereby indicating a GSH-conjugation attributed with high rates. The optimum pH and temperature for the catalytic activity of the rRpGSTμ protein were 7.7 and 37°C, respectively. The effect of two inhibitors, Cibacron blue and hematin, on the activity of rRpGSTμ was evaluated and the IC50 values of 0.65 μM and 9 μM, respectively, were obtained. While RpGSTμ transcripts were highly expressed in gills and hemocytes, a significant elevation in mRNA levels was detected in these tissues after lipopolysaccharide (LPS), polyinosinic-polycytidylic acid (poly I:C) and live bacterial (Vibrio tapetis) challenges. These findings collectively suggest that RpGSTμ functions as a potent detoxifier of xenobiotic toxicants present in the aquatic environment, and that its mRNA expression could be modulated by pathogenic stress signal(s).

Cloning, expression and identification of two glutathione S-transferase isoenzymes from Perna viridis

Glutathione S-transferases (GSTs; EC 2.5.1.18) are phase II enzymes involved in major detoxification reactions of xenobiotic in many organisms. In the present study, two classes of GSTs (PvGST1 and PvGST2) were cloned from P. viridis by rapid amplification of cDNA ends method. Sequence alignments and phylogenetic analysis together supported that PvGST1 and PvGST2 belonged to the pi and omega classes, respectively. The PvGST1 cDNA was 1214 nucleotides (nt) in length and contained a 618 nt open reading frame (ORF) encoding 206 amino acid residues, and had 46 nt of 5'-untranslated region (UTR) and a 3' UTR of 550 nt including a tailing signal (AATAAA) and a poly (A) tail. The molecular mass of the predicted PvGST1 was 23.815kDa, with the calculated isoelectric point being 5.39. PvGST2 was 1093bp, consisting of a 5' UTR of 13bp, a 3' UTR of 246bp and an ORF of 834bp. The deduced protein was composed of 278 amino acids, with an estimated molecular mass of 32.476kDa and isoelectric point of 8.88. Tissue distribution analysis of the PvGST1 and PvGST2 mRNA revealed that the GST expression level was higher in digestive gland and gonad, while lower in gill and mantle in both genders. Molecular modeling analysis of two GSTs implicated their various functions account for their different enzymatic features.

Differentially expressed proteins in the skin mucus of Atlantic cod (Gadus morhua) upon natural infection with Vibrio anguillarum

Background

Vibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces (gut, skin and gills) of fish. Therefore it is necessary to investigate the role of different mucosal components in fish upon V. anguillarum infection. The present study has two parts; in the first part we analyzed the differential expression of skin mucus proteins from Atlantic cod naturally infected with V. anguillarum using two dimensional gel electrophoresis coupled with mass spectrometry. In the second part, a separate bath challenge experiment with V. anguillarum was conducted to assess the mRNA levels of the genes in skin tissue, corresponding to the selected proteins identified in the first part.

Results

Comparative proteome analysis of skin mucus of cod upon natural infection with V. anguillarum revealed key immune relevant proteins like calpain small subunit 1, glutathione-S-transferase omega 1, proteasome 26S subunit, 14-kDa apolipoprotein, beta 2-tubulin, cold inducible RNA binding protein, malate dehydrogenase 2 (mitochondrial) and type II keratin that exhibited significant differential expression. Additionally a number of protein spots which showed large variability amongst individual fish were also identified. Some of the proteins identified were mapped to the immunologically relevant JNK (c-Jun N-terminal kinases) signalling pathway that is connected to cellular events associated with pathogenesis. A bath challenge experiment with V. anguillarum showed differential expression of beta 2-tubulin, calpain small subunit 1, cold inducible RNA binding protein, flotillin1, and glutathione S-transferase omega 1 transcripts in the skin tissue of cod during early stages of infection.

Conclusions

Differentially expressed proteins identified in the cod skin mucus point towards their possible involvement in V. anguillarum pathogenesis. The role of some of these proteins in vibriosis in cod described in this paper can be considered unconventional with respect to their established functions in higher vertebrates. Based on the differential expression of these proteins they are possibly important components of fish defence against bacteria and innate immunity at large. The feasibility of utilizing these proteins/genes as markers of bacterial infection or stress in cod needs to be explored further.

A novel molluscan sigma-like glutathione S-transferase from Manila clam, Ruditapes philippinarum: cloning, characterization and transcriptional profiling

Glutathione S-transferases (GSTs) are versatile enzymes, act as primary intracellular detoxifiers and contribute to a broad range of physiological processes including cellular defense. In this study, a full-length cDNA representing a novel sigma-like GST was identified from Manila clam, Ruditapes philippinarum (RpGSTσ). RpGSTσ (884 bp) was found to possess an open reading frame of 609 bp. The encoded polypeptide (203 amino acids) had a predicted molecular mass of 23.21 kDa and an isoelectric point of 7.64. Sequence analysis revealed two conserved GST domain profiles in N- and C-termini. Alignment studies revealed that the identity between deduced peptides of RpGSTσ and known GSTσ members was relatively low (<35%), except a previously identified Manila clam GSTσ isoform (87.2%). Phylogenetic analysis indicated that RpGSTσ clustered together with molluscan GSTσ homologs, which were closely related to insect GSTσs. The RpGSTσ was subsequently cloned and expressed as recombinant protein, in order to characterize its biological activity. The recombinant RpGSTσ exhibited characteristic glutathione conjugating catalytic activity toward 1-chloro-2,4-dinitrobenzene, 3,4-dichloronitrobenzene and ethacrynic acid. It had an optimal pH and temperature of 8.0 and 35 °C, respectively. Expression profiles under normal conditions and in response to lipopolysaccharide-, poly I:C- and Vibrio tapetis-challenges were also investigated. RpGSTσ demonstrated a differential tissue distribution with robust transcription in gills of normal animals. We explored potential association of GSTσ in cellular defense during bacterial infection and found that in challenged clams, RpGSTσ gene was significantly induced in internal and external tissues, in conjunction with manganese- as well as copper-zinc superoxide dismutase (MnSOD and CuZnSOD) genes. Moreover, the induction was remarkably higher in hemocytes than in gill. Collectively, our findings suggested that RpGSTσ could play a significant role in cellular defense against oxidative stress caused by bacteria, in conjunction with other antioxidant enzymes, such as SODs.