Identification of Partitivirus-like RdRPs in the Brevipalpus yothersi Genome Supports Viral-to-Arthropod Horizontal Gene Transfer.

RNA-dependent RNA polymerases (RdRPs) are essential enzymes involved in RNA virus replication and eukaryotic RNA silencing. They are generally absent in vertebrates but present in some invertebrate lineages, such as nematodes and certain arthropods. Brevipalpus yothersi is a phytophagous mite of agricultural relevance due to its role as a vector of plant-infecting viruses. We have identified two RdRPs on the genome of this mite species that, unexpectedly, are not of eukaryotic origin. Phylogenetic reconstruction and comparisons of 3D protein structures revealed similarity with viral RdRPs of the Partitiviridae family. Both RdRPs retain conserved catalytic motifs at the protein sequence level, and expression was confirmed by RNAseq and qPCR across mite developmental stages, with a peak during the nymphal stage. K-mer profiles showed similarity with mite endogenous genes, suggesting gene amelioration after the integration, or being derived from a viral donor already adapted to the mite. Our study also identified orthologs in other Brevipalpus species, but not in other Acari relatives, supporting that the horizontal gene transfer event is circumscribed to the Brevipalpus genus. These findings highlight an intriguing case of viral gene domestication in arthropods that might influence their developmental biology and the host-virus interaction.