Abstract Detail


Li, Zheng [1], Barker, Michael [1].

Why do homosporous ferns have high numbers of chromosomes?

One of the long-standing mysteries in plant evolution is the origin of chromosome number variation across the vascular plant phylogeny. The homosporous ferns have an average haploid chromosome number of n = 57, threefold higher than angiosperms which have an average of n = 16. Based on isozyme data, it has been hypothesized that ferns have gone through multiple rounds of paleopolyploidy rather than other alternatives such as ancestral high chromosome numbers or ascending aneuploidy. Our previous analyses found evidence for multiple ancient whole genome duplications (WGDs) in ferns and lycophytes. Here, we assembled a large dataset of 157 fern and lycophyte transcriptomes that represents all major lineages of ferns and lycophytes. Using a combination of gene age distribution and phylogenomic analyses, we inferred ancient WGDs across the evolutionary history of ferns and lycophytes. We found evidence for over 30 ancient WGDs and confirm most ferns and lycophytes are ancient polyploids. Across the phylogeny, we estimated that the average fern species has experienced 4 rounds of ancient polyploidy. We also found a similar level of polyploid ancestry for homosporous and heterosporous ferns, a surprising result given the difference in their chromosome numbers. Ferns and angiosperms also appear to have experienced a similar number of rounds of paleopolyploidy. This suggests homosporous ferns have more chromosomes than angiosperms because of multiple rounds of ancient WGD without chromosome loss. We confirmed this result using a phylogenetic analysis of chromosome numbers across the fern phylogeny. Combining phylogenomic and chromosome number evolution analyses, these results enhance our understanding of the mode and tempo of vascular plant genome evolution.

1 - University of Arizona, Department Of Ecology & Evolutionary Biology, P.O. Box 210088, Tucson, Arizona, 85721, US

chromosome number
whole genome duplication
homosporous fern

Presentation Type: Oral Paper
Number: 0001
Abstract ID:436
Candidate for Awards:None

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