Two novel glutathione S-transferase (GST) genes in the toxic marine dinoflagellate Alexandrium pacificum and their transcriptional responses to environmental contaminants

Abstract

The present study identified two novel glutathione S-transferase (GST) genes from the toxic dinoflagellate Alexandrium pacificum and examined their molecular characteristics and transcriptional responses to algicides and environmental contaminants. Bioinformatic analysis revealed that both ApGSTs are cytosolic, belonging to the chi-like class (ApGST1) and an undefined class (ApGST2). The overall expression of ApGSTs showed similar patterns depending on the exposed contaminants, while they were differently regulated by polychlorinated biphenyl (PCB). Copper treatments (CuCl₂ and CuSO₄) did not significantly induce the expression of ApGSTs. The highest up-regulations of ApGST1 and ApGST2 were under 6-h treatments of 0.10 and 0.50 mg L^-1 NaOCl. Interestingly, only ApGST1 increased significantly after 0.10, 0.50, and 1.00 mg L^-1 of PCB exposure (6 h). Intracellular reactive oxygen species (ROS) increased considerably under NaOCl; however, it was not significantly higher in the PCB-treated cells. GST activity was increased by NaOCl and PCB treatments, but only PCB caused apoptosis. These results suggest that GSTs are involved in the first line of phase II detoxification, protecting dinoflagellate cells against oxidative damage.

Keywords: Alexandrium pacificum; Contaminants; Detoxification; Glutathione S-transferase; Reactive oxygen species; Stress response; Transcriptional responses.