# Could Horizontal Gene Transfer Explain 5S rDNA Similarities Between Frogs and Worm Parasites?

## TL;DR

This paper explores whether horizontal gene transfer explains similar 5S rDNA sequences in frogs and their flatworm parasites.

## Contribution

The study proposes a cross-phylum horizontal gene transfer event between frogs and their parasites based on 5S rDNA similarities.

## Key findings

- A 5S rDNA sequence from the frog Xenopus laevis is highly similar to that of its parasite Protopolystoma xenopodis.
- Phylogenetic analysis shows the parasite's 5S rDNA clusters with frog sequences, suggesting HGT.
- No evidence of contamination in the parasite's genome supports the HGT hypothesis.

## Abstract

Horizontal gene transfer (HGT), the non-Mendelian transfer of genetic material between organisms, is relatively frequent in prokaryotes, whereas its extent among eukaryotes remains unclear. Here, we raise the hypothesis of a possible cross-phylum HGT event involving 5S ribosomal DNA (rDNA). A specific type of 5S rDNA sequence from the anuran Xenopus laevis was highly similar to a 5S rDNA sequence of the genome of its flatworm parasite Protopolystoma xenopodis. A maximum likelihood analysis revealed phylogenetic incongruence between the gene tree and the species trees, as the 5S rDNA sequence from Pr. xenopodis was grouped along with the sequences from the anurans. Sequence divergence analyses of the gene region and non-transcribed spacer also agree with an HGT event from Xenopus to Pr. xenopodis. Additionally, we examined whether contamination of the Pr. xenopodis genome assembly with frog DNA could explain our findings but found no evidence to support this hypothesis. These findings highlight the possible contribution of HGT to the high diversity observed in the 5S rDNA family.