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Abstract We describe four ancient polyploidy events where the descendant taxa retain many more duplicated gene copies than has been seen in other paleopolyploidies of similar ages. Using POInT (the Polyploidy Orthology Inference Tool), we modeled the evolution of these four events, showing that they do not represent recent independent polyploidies despite the rarity of shared gene losses. We find that these events have elevated rates of interlocus gene conversion and that these gene conversion events are spatially clustered in the genomes. Regions of gene conversion also show very low synonymous divergence between the corresponding paralogous genes. We suggest that these genomes have experienced a delay in the return to a diploid state after their polyploidies. Under this hypothesis, homoeologous exchanges between the duplicated regions created by the polyploidy persist to this day, explaining the high rates of duplicate retention. Genomes with these characteristics arguably represent a new class of paleopolyploid taxa because they possess evolutionary patterns distinct from the more common and well-known paradigm of the rapid loss of many of the duplicated pairs created by polyploidy.
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Ancient polyploidy and low rate of chromosome loss explain the high chromosome numbers of homosporous ferns
A longstanding question in plant evolution is why ferns have many more chromosomes than angiosperms. The leading hypothesis proposes that ferns have ancient polyploidy without chromosome loss or gene deletion to explain the high chromosome numbers of ferns. Here, we test this hypothesis by estimating ancient polyploidy frequency, chromosome evolution, protein evolution in meiosis genes, and patterns of gene retention in ferns. We found similar rates of paleopolyploidy in ferns and angiosperms from independent phylogenomic and chromosome number evolution analyses, but lower rates of chromosome loss in ferns. We found elevated evolutionary rates in meiosis genes in angiosperms, but not in ferns. Finally, we found some evidence of parallel and biased gene retention in ferns, but this was comparatively weak to patterns in angiosperms. This work provides genomic evidence supporting a decades-old hypothesis on fern genome evolution and provides a foundation for future work on plant genome structure.
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- Award ID(s):
- 2209073
- PAR ID:
- 10639428
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.1101/2024.09.23.614530
