Development of the transcriptome for a sediment ecotoxicological model species, Chironomus dilutus

Chironomus dilutus is a prominent model species in conventional sediment toxicity testing and sediment contamination diagnosis. However, lack of genomic data significantly limited its application in identifying toxicological mode of action (MOA) and molecular biomarkers of toxicants. Here the transcriptome of C. dilutus in full life span and both sexes (1st, 2nd, 3rd and 4th instar larvae, pupae, and adults) were developed and temporal gene expression across adjacent life stages were investigated to understand the regulation of development. Furthermore, transcriptional response of Midges (the 4th instar larvae) exposed to chemicals of different MOAs (CdCl₂, nonylphenol and triclosan) were profiled based on the reference transcriptome. Consequently, a complete transcriptome of 31132 unigenes with N50 of 3117bp, covering 98.8% of the arthropod single-copy orthologs were assembled. While 364 genes were differentially expressed among adjacent larval stages, 7142 and 2127 of transcripts were significantly changed for the transition of larvae-pupae and pupae-adults, respectively. Finally, chemical-specific gene expression profile were identified in the midges, showed its potential in classifying distinct contaminants. Overall, the comprehensive transcriptome of C. dilutus developed here could not only facilitate the mechanistic understanding of environmental toxicants during critical life stage of aquatic insects, but also provide molecular diagnostic tools in sediment ecotoxicology.