Life without a Sporophyte: The Origin and Genomic Consequences of Asexual Reproduction in a Gametophyte-Only Fern

Premise of research. The vast majority of eukaryotes reproduce by sexual reproduction, which is accompanied by meiotic recombination. Asexual reproduction, including the loss of meiosis, has been well characterized in several animal lineages but is vastly understudied in plants and particularly in the gametophyte life stage. Here, we explore the genomic consequences of strict clonal reproduction in the gametophyte-only fern Vittaria appalachiana. Methodology. Using publicly available transcriptome assemblies, we assessed how asexual reproduction can alter genomic features by comparing the transcriptomes of the asexually reproducing V. appalachiana (Pteridaceae) with sexually reproducing species in the same family, including congener Vittaria lineata. We explored several hypotheses relating asexual reproduction to the efficacy of purifying selection, transposable element load, GC-biased gene conversion, and the role of whole-genome duplications (WGDs). Pivotal results. We found putative support for predicted genomic consequences of asexual reproduction, including decreased efficacy of purifying selection (particularly in genes related to the cell cycle), altered transposable element load, and decreased GC content in V. appalachiana. We identified two putative WGDs, shared by Pteridaceae and the most recent common ancestor of the Vittaria genus, which may have contributed to V. appalachiana’s persistence over evolutionary time without sexual reproduction. Conclusions. Vittaria appalachiana is a gametophyte-only fern that is well suited to address fundamental questions regarding the long-term genomic effects of asexual reproduction in ferns, where this phenomenon has had little scientific attention in plants. This initial exploration into the genomic consequences of asexual reproduction is one of the first in ferns and highlights several avenues for future research.