Glutathione S-transferase genes in scallops and their diverse expression patterns after exposure to PST-producing dinofagellates

The glutathione S-transferases (GSTs) are a superfamily of enzymes that function in cellular protection against toxic substances and oxidative stress. Bivalves could accumulate high concentration of paralytic shellfish toxins (PSTs) from harmful algae. To understand the possible involvement of GSTs in protecting bivalves during PST accumulation and metabolism,the GST genes were systemically analyzed in two cultured scallops,Azumapecten farreri and Mizuhopecten yessoensis,which were reported for PST deposition during harmful algae bloom. A total of 35 and 37 GSTs were identified in A. farreri (AfGSTs) and M. yessoensis (MyGSTs) genome,respectively,and the expansion of the sigma class from the cytosolic subfamily was observed. In both scallop species,sigma class GSTs showed higher expression than other members. The high GSTs expression was detected mainly during/after larvae stages and in the two most toxic organs,hepatopancreas and kidney. After ingesting PST-producing dinoflagellates,all the regulated AfGSTs in the hepatopancreas were from the sigma class,but with opposite regulation pattern between Alexandrium catenella and A. minutum exposure. In scallop kidneys,where PSTs transformed into higher toxicity,more AfGSTs were regulated than in the hepatopancreas,and most of them were from the sigma class,with similar regulation pattern between A. catenella and A. minutum exposure. In M. yessoensis exposed to A. catenella,MyGST-σ2 was the only up-regulated MyGST in both hepatopancreas and kidney. Our results suggested the possible diverse function of scallop GSTs and the importance of sigma class in the defense against PSTs,which would contribute to the adaptive evolution of scallops in marine environments.