Chromosome-level genome assembly of the synanthropic fly Chrysomya megacephala: insights into oviposition location.

The oriental latrine fly, Chrysomya megacephala (Diptera: Calliphoridae), is a medically important synanthropic blow fly species characterized by its necrophagy and coprophagy, often observed near carrion and animal feces. Notably, C. megacephala always arrives at carcass earlier than other species. To elucidate the underlying mechanisms behind the host choice in C. megacephala, we present the chromosome-scale genome assembly for this species. The genome size is 816.79 Mb, with a contig N50 of 1.60 Mb. The Hi-C data were anchored to six chromosomes, accounting for 99.93% of the draft assembled genome. Comparative genomic analysis revealed significant expansions in pathways of ligand-gated ion channel activity, passive transmembrane transporter activity, and protein methyltransferase activity, which may be closely associated with host localization and oviposition. After identifying 69 odor-binding proteins (OBPs) in the assembled genome, phylogenetic analysis showed that DmelOBP99b and CmegOBP99b exhibited high homology. Transcriptome analysis demonstrated that the relative expression of CmegOBP99b was consistently the highest during the metamorphosis, and RT-qPCR further confirmed the similar results. Additionally, CmegOBP99b exhibited a strong binding affinity to DMDS (dimethyl disulfide) as determined by molecular docking. To determine the protein expression level of CmegOBP99b in various body parts, we prepared recombinant CmegOBP99b protein and anti-CmegOBP99b polyclonal antibodies. Western blot analysis showed that CmegOBP99b was significantly expressed in the female's head compared to other parts, which is consistent with RT-qPCR results. Therefore, CmegOBP99b may be the primary odor-binding protein responsible for olfactory recognition and the behavioral coordination of C. megacephala. This study not only provides valuable insights into the molecular mechanisms of oviposition localization in C. megacephala but also facilitates further research into the genetic diversity and phylogeny of the Calliphoridae family.