Oral Paper

         Pteridology

Seed-free Synteny: A history of genomic stasis in homosporous ferns and lycophytes

Presenting Author
David Wickell
Description
Polyploidy both ancient and recent have long been seen as important drivers of plant evolution. However, a related and equally important process is that of diploidization that occurs following whole genome duplication (WGD). Diploidization is characterized by extensive changes to gene content, gene order, chromatin organization, and chromosome structure affecting multiple biological processes including cell division, gene expression, and dosage effects. While the importance of polyploidy has been extensively studied across the tree of life relatively little is known about factors driving diploidization or how it varies between groups of plants. This is especially true among seed-free lineages where a paucity of genome assemblies has hindered investigation into the genomic signatures of large-scale duplication. With the recent publication of several fern and lycophyte genomes we are beginning to be able to examine the downstream effects of WGD on genomic organization in these deeply diverged and evolutionarily important lineages. Our analyses of the tree fern Alsophila spinulosa as well as lycophytes Huperzia asiatica  and Diphasiastrum complanatum in the family Lycopodiaceae have provided evidence that genomic rearrangement following WGD occurs at a much slower rate in certain homosporous groups of ferns and lycophytes with syntenic relationships being preserved over hundreds of millions of years. Furthermore, this genomic stasis appears to be accompanied by significantly lower substitution rates in both lineages. While the mechanisms for this evolutionary slow-down remain elusive our characterization of diploidization in seed free plants provides an interesting counterpoint to similar studies in angiosperms that have found rapid rates of gene loss and rearrangement immediately following polyploidization.