A novel insect-infecting virga/nege-like virus group and its pervasive endogenization into insect genomes.

Insects are the host and vector of diverse viruses including those that infect vertebrates, plants, and fungi. Recent wide-scale transcriptomic analyses have uncovered the existence of a number of novel insect viruses belonging to an alphavirus-like superfamily (virgavirus/negevirus-related lineage). In this study, through an in silico search using publicly available insect transcriptomic data, we found numerous virus-like sequences related to insect virga/nege-like viruses. Phylogenetic analysis showed that these novel viruses and related virus-like sequences fill the major phylogenetic gaps between insect and plant virga/negevirus lineages. Interestingly, one of the phylogenetic clades represents a unique insect-infecting virus group. Its members encode putative coat proteins which contained a conserved domain similar to that usually found in the coat protein of plant viruses in the family Virgaviridae. Furthermore, we discovered endogenous viral elements (EVEs) related to virga/nege-like viruses in the insect genomes, which enhances our understanding on their evolution. Database searches using the sequence of one member from this group revealed the presence of EVEs in a wide range of insect species, suggesting that there has been prevalent infection by this virus group since ancient times. Besides, we present detailed EVE integration profiles of this virus group in some species of the Bombus genus of bee families. A large variation in EVE patterns among Bombus species suggested that while some integration events occurred after the species divergence, others occurred before it. Our analyses support the view that insect and plant virga/nege-related viruses might share common virus origin(s).