Genome-wide identification glutathione-S-transferase gene superfamily in Daphnia pulex and its transcriptional response to nanoplastics.

Glutathione S-transferases (GSTs) are key multifunctional phase II detoxification enzymes involved in the regulation of growth, development, and stress responses. However, the knowledge of GSTs in the model invertebrate organism Daphnia pulex at the genomic level remains limited. In the present study, 35 GST genes were identified in D. pulex (Dp-GST), belonging to eight subfamilies, with the sigma, mu, and delta/epsilon subfamilies constituting approximately 29 %, 20 %, and 20 % of the GST superfamily, respectively. Chromosome tandem duplication of genes within the same subfamily was observed, which may be the main force driving GST expansion in D. pulex. DpGST genes showed different expression patterns in response to nanoplastic exposure for 96 h and 21 days. Some homologous GST genes in D. pulex showed similar expression patterns in response to nanoplastic exposure, likely owing to their unique motifs. For example, motif 9 is found in all delta/epsilon GST genes, whereas motifs 1, 2, 3, 5, and 7 are highly conserved in sigma GST genes. The characterization of D. pulex GSTs extending the knowledge of GST-mediated environmental contaminants, especially nanoplastics.