Abstract
Recently, nematode viruses infecting Caenorhabditis elegans have been reported from the family Nodaviridae, the first nematode viruses described. Here, we report the observation of a novel endogenous viral element (EVE) in the genome of Bursaphelenchus xylophilus, a plant parasitic nematode unrelated to other nematodes from which viruses have been characterised. This element derives from a different clade of nodaviruses to the previously reported nematode viruses. This represents the first endogenous nodavirus sequence, the first nematode endogenous viral element, and significantly extends our knowledge of the potential diversity of the Nodaviridae. A search for endogenous elements related to the Nodaviridae did not reveal any elements in other available nematode genomes. Further surveillance for endogenous viral elements is warranted as our knowledge of nematode genome diversity, and in particular of free-living nematodes, expands.
Highlights
The first evidence that nematodes might host viruses were a number of reports of virus-like particles by electron microscopy
Our results suggest that the RNA1 transcript of a nematode-infectious nodavirus infecting the germ line of B. xylophilus has been reverse transcribed by a cellular reverse transcriptase activity, captured by non-homologous recombination by an long terminal repeat (LTR) retroelement and inserted into the host genome
This is the first evidence of a nematode nodavirus outside Caenorhabditis spp., expanding the known host-range of nodaviridae; the ancestral virus our element descended from represents a distinct lineage from the Caenorhabditis viruses or any other nodavirus
Summary
The first evidence that nematodes might host viruses were a number of reports of virus-like particles by electron microscopy (see Bird and Bird[1] pp276280 for a review of this early literature[2]). Research on these viruses has demonstrated that they infect intestinal cells in the worm[7], have revealed a strikingly different capsid structure of Orsay (one of the C. elegans viruses) to the arthropod betanodaviruses[8] and is starting to investigate the molecular biology[9] and even develop approaches for genetic manipulation[10] of this virus Following this discovery, a number of other potential nematode viruses have been described, significantly expanding the diversity of both nematode hosts and of the viruses infecting them. Study of ‘fossil’ copies of viruses has given valuable insights into the evolution of both viruses[19,20,21] and hosts[22,23]
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