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Pelosi, Jessie [1], Barbazuk, W. Brad [2], Sessa, Emily [3].

Life without a sporophyte: revisiting the genomic consequences of asexual reproduction and the origin of Vittaria appalachiana .

Meiotic recombination is a powerful force that shapes genome evolution in sexually reproducing organisms. In the absence of sexual reproduction several deleterious effects may be observed, including (1) decreased efficacy of purifying selection, (2) decreased GC content bias, and (3) altered transposable element (TE) load. These patterns have been widely observed in ancient asexual lineages of animals such as bdelloid rotifers and orbatid mites, but have not been thoroughly investigated in plants, which are often functional (rather than obligate) asexuals. Vittaria appalachiana is a fern that exists solely in the gametophyte life phase and reproduces through the production of somatic gemmae. It has been hypothesized that the loss of the sporophyte phase in this group occurred during the Last Glacial Maximum, suggesting that the switch to fully asexual reproduction occurred between 10,000 and 20,000 years ago. In order to investigate the origins of V. appalachiana and determine if functional changes are associated with asexual genome evolution in this species, we downloaded transcriptome assemblies from the 1KP project from Pteridaceae including Vittaria appalachiana and V. lineata (sexual congener), and the outgroup Asplenium platyneuron. To study the effect of asexual reproduction, we compared GC bias, TE content, and selective pressure (as measured by dN/dS ratios) between the two Vittaria species using single copy orthologs. To elucidate the origins of V. appalachiana we examined gene family evolution and polyploidy across Pteridaceae. We found that V. appalachiana and V. lineata share two WGDs, one at the base of Vittaria and one at the base of Pteridaceae, contradicting an earlier hypothesis that V. appalachiana is derived from a neo-autopolyploidy event. Furthermore, V. appalachiana has a significantly greater GC bias and TE content, and has genes under less effective purifying selection than V. lineata. Specifically, orthologs under weaker purifying selection were found to be associated with male gamete generation. Analyses of gene family evolution across Pteridaceae showed that families involved with DNA repair, cell wall organization, and cell shape were contracted or lost in V. appalachiana, while gene families with functions related to cold/osmotic stress and cytoskeletal organization were expanded or gained. While the genomic consequences of asexual reproduction are expected to be more pronounced in ancient asexuals, our results highlight several genomic changes associated with the recent loss of sexual reproduction and changes in life history traits in V. appalachiana.

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1 - University Of Florida, Biology, 220 Bartram Hall PO Box 118525, Gainesville, FL, 32611, United States
2 - University of Florida, Department of Biology , 220 Bartram Hall PO Box 118525, Gainesville, FL, 32611, USA
3 - University Of Florida, Biology, Box 118525, 521A Bartram Hall, Gainesville, FL, 32611, United States


Presentation Type: Oral Paper
Session: PTR2, Pteridology II
Location: /
Date: Monday, July 19th, 2021
Time: 2:15 PM(EDT)
Number: PTR2004
Abstract ID:47
Candidate for Awards:Edgar T. Wherry award

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