Abstract Detail

Questioning Species and Species Complexes: A Colloquium in Honor of Dr. R. James Hickey

Li, Zheng [1], Barker, Michael [2].

Homosporous ferns and lycophytes with high chromosome numbers are paleopolyploids.

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 over 30 ancient WGDs across the evolutionary history of ferns and lycophytes. These results are consistent with syntenic evidence from the Azolla and Salvinia genomes. 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 ferns and angiosperm, a surprising result given the difference in their average chromosome numbers. Confirmed by a phylogenetic analysis of chromosome numbers across the fern phylogeny, this suggests homosporous ferns have more chromosomes than angiosperms because of multiple rounds of ancient WGD without chromosome loss. To understand the difference of chromosome loss between homosporous ferns and angiosperms, we further investigate genes that might associate with chromosome loss in vascular plants. Combining different approaches, these results enhance our understanding of the mode and tempo of vascular plant genome evolution.

1 - University Of Arizona, Department Of Ecology And Evolutionary Biology, P.O. Box 210088, Tucson, AZ, 85721, United States
2 - Department Of Ecology & Evolutionary Biology, P.O. Box 210088, Tucson, AZ, 85721, United States

Keywords:
ferns
Lycophytes
chromosome numbers 
paleopolyploid
Whole genome duplication.

Presentation Type: Colloquium Presentations
Session: CO12, Questioning Species and Species Complexes: A Colloquium in Honor of Dr. R. James Hickey
Location: San Luis 1/Starr Pass
Date: Wednesday, July 31st, 2019
Time: 4:30 PM
Number: CO12012
Abstract ID:494
Candidate for Awards:None