The genome of the marine monogonont rotifer Brachionus plicatilis: Genome-wide expression profiles of 28 cytochrome P450 genes in response to chlorpyrifos and 2-ethyl-phenanthrene.

Brachionus spp. (Rotifera: Monogononta) are globally distributed in aquatic environments and play important roles in the aquatic ecosystem. The marine monogonont rotifer Brachionus plicatilis is considered a suitable model organism for ecology, evolution, and ecotoxicology. In this study, we assembled and characterized the B. plicatilis genome. The total length of the assembled genome was 106.9 Mb and the number of final scaffolds was 716 with an N50 value of 1.15 Mb and a GC content of 26.75%. A total of 20,154 genes were annotated after manual curation. To demonstrate the use of whole genome data, we targeted one of the main detoxifying enzyme of phase I detoxification system and identified in a total of 28 cytochrome P450 s (CYPs). Based on the phylogenetic analysis using the maximum likelihood, 28 B. plicatilis-CYPs were apparently separated into five different clans, namely, 2, 3, 4, mitochondrial (MT), and 46 clans. To better understand the CYPs-mediated xenobiotic detoxification, we measured the mRNA expression levels of 28 B. plicatilis CYPs in response to chlorpyrifos and 2-ethyl-phenanthrene. Most B. plicatilis CYPs were significantly modulated (P < 0.05) in response to chlorpyrifos and 2-ethyl-phenanthrene. In addition, xenobiotic-sensing nuclear receptor (XNR) response element sequences were identified in the 5 kb upstream of promoter regions of 28 CYPs from the genome of B. plicatilis, indicating that these XNR can be associated with detoxification of xenobiotics. Overall, the assembled B. plicatilis genome presented here will be a useful resource for a better understanding the molecular ecotoxicology in the view of molecular mechanisms underlying toxicological responses, particularly on xenobiotic detoxification in this species.