A novel glutathione S-transferase Gtt2 class from the marine toxic dinoflagellate Alexandrium pacificum and its roles in algicide exposures

In the present study, we identified a novel cytosolic glutathione S-transferase ( GST ) gene, Gtt2 , from the marine dinoflagellate Alexandrium pacificum and evaluated its transcriptional responses to six toxic chemicals. The full-length cDNA sequence of ApGtt2 was 1306 base pairs (bp), encoding 289 amino acids with a predicted molecular weight of 32.76 kDa. The genomic coding region of the gene contained a 785-bp intron. Bioinformatics analysis revealed that ApGtt2 has a thioredoxin fold domain at the N-terminus, showing a characteristic feature of cytoplasmic GSTs. Phylogenetic analysis revealed that ApGtt2 belongs to the Gtt2 class, which is distinct from previously characterized GST classes. In addition, transcriptional changes in ApGtt2 showed differential regulation under short term exposure to toxic chemicals. The gene responded to certain chemicals (CuCl 2 , CuSO 4 , etc.); in particular, gene expression increased significantly by 2.52-fold after 6 h of exposure to 0.05 mg/L metazachlor (MZC) and by 7.65-fold after 6 h of treatment with 0.1 mg/L NaOCl treatments. Also, both MZC and NaOCl significantly triggered reactive oxygen species (ROS) levels (5.99- and 14.86-fold) and enhanced total GST activity (2.93- and 3.94-fold). These findings suggest that cytosolic ApGtt2 may be involved in the early response to chemical stress, serving as a key molecular defense that enhances the ecological adaptability to environmental contaminants. To our knowledge, this is the first report of a cytosolic Gtt2 in a marine dinoflagellate and of its transcriptional regulation under chemical stress.