Structurally distinct mitoviruses: are they an ancestral lineage of the Mitoviridae exclusive to arbuscular mycorrhizal fungi (Glomeromycotina)?

Mitoviruses in the family Mitoviridae are the mitochondria-replicating"naked RNA viruses" with genomes encoding only the replicase RNA-dependent RNApolymerase (RdRp) and prevalent across fungi, plants, and invertebrates. Arbuscularmycorrhizal fungi in the subphylum Glomeromycotina are obligate plant symbiontsthat deliver water and nutrients to the host. We discovered distinct mitoviruses inglomeromycotinian fungi, namely "large duamitovirus," encoding unusually large RdRpwith a unique N-terminal motif that is endogenized in some host genomes. More than400 viral sequences similar to the large duamitoviruses are present in metatranscriptome databases. They are globally distributed in soil ecosystems, consistent with thecosmopolitan distribution of glomeromycotinian fungi, and formed the most basal cladeof the Mitoviridae in phylogenetic analysis. Given that glomeromycotinian fungi are theonly confirmed hosts of these viruses, we propose the hypothesis that large duamitoviruses are the most ancestral lineage of the Mitoviridae that have been maintainedexclusively in glomeromycotinian fungi.