A chromosome level genome assembly of Propsilocerus akamusi to understand its response to heavy metal exposure

Chironomidae species are universally used for studying the impact of pollutants in aquatic systems. The nonbiting midge Propsilocerus akamusi is often found in urban streams and is suitable for use as a toxicological bioindicator. However, few studies have previously examined metal stress in this species. We sequenced the genome of this urban midge to address this question. Here, we present the first chromosome-level genome of P. akamusi, obtained from Illumina short-read and PacBio long-read sequences with Hi-C technology. The size of the very small assembled genome was 85.83 Mb with a contig N50 of 6.2 Mb and a scaffold N50 of 26.1 Mb. This assembly revealed significant expansion of haemoglobin (Hb) genes, some of which formed large tandem repeats. Transcriptomic studies for copper tolerance identified four genes in the tandem array that were highly expressed, all of which presented intron loss. This characteristic might highlight the potential role of Hb genes in copper tolerance. Additionally, detoxification genes, chemosensory genes and heat shock protein genes of this midge were identified, some of which are associated with metal stress. The high-quality assembled genome of P. akamusi and the transcriptomic analyses provide new insight into the molecular mechanisms of heavy metal stress. Our comparison of the P. akamusi genome with other dipteran genomes provides valuable resources for understanding the evolutionary history, genetics, and ecology of this species as well as those of other midges.