Chromosomal scale assembly of parasitic wasp genome reveals symbiotic virus colonization

Endogenous viruses form an important proportion of eukaryote genomes and a source of novel functions. How large DNA viruses integrated into a genome evolve when they confer a benefit to their host, however, remains unknown. Bracoviruses are essential for the parasitism success of parasitoid wasps, into whose genomes they integrated similar to 103 million years ago. Here we show, from the assembly of a parasitoid wasp genome at a chromosomal scale, that bracovirus genes colonized all ten chromosomes of Cotesia congregata. Most form clusters of genes involved in particle production or parasitism success. Genomic comparison with another wasp, Microplitis demolitor, revealed that these clusters were already established similar to 53mya and thus belong to remarkably stable genomic structures, the architectures of which are evolutionary constrained. Transcriptomic analyses highlight temporal synchronization of viral gene expression without resulting in immune gene induction, suggesting that no conflicts remain between ancient symbiotic partners when benefits to them converge. Jeremy Gauthier et al. present the chromosome scale assembly of the genome of the parasitic wasp C. congregata and show that bracovirus genes have colonized all ten chromosomes. Comparison with genome scaffolds of another wasp reveals a striking stability of these regions over similar to 53 million years, suggesting strong evolutionary constraints.

Automated summary

Endogenous viruses make up a significant portion of eukaryote genomes and provide new functions, although the evolution of large DNA viruses integrated into genomes that benefit their host remains unknown. A study on parasitoid wasps reveals that bracovirus genes have colonized all ten chromosomes, with these gene clusters being established over 53 million years ago and showing remarkable stability in genomic structures constrained by evolution. Transcriptional analysis shows temporal synchronization of viral gene expression without immune gene induction, suggesting a lack of conflict between ancient symbiotic partners.