Biodiversity encompasses all life on Earth, yet our knowledge regarding the number of species composing the various branches of the tree of life varies, with tiny organisms marking the lower end of the spectrum. Bryophytes are a diverse component of most ecosystems around the globe. As land plants, their evolutionary history began some 500 million years ago, but much of the current species diversity is of rather recent origin, revealing that despite their small stature and overall low morphological complexity these organisms are evolutionarily successful. This prompts the questions, what drives their evolution, or what is natural selection acting on and what triggers innovation in the genetic toolbox of mosses? We explored these questions using a moss that is widespread in North America, and Western Europe, a moss that can be easily grown, and that may harbor several strains differing by the size of their genome. Physcomitrium pyriforme is an annual moss, growing in seasonal habitats, developing its vegetative plants in the fall, and entering dormancy following sexual reproduction and resuming growth in the spring.

Intellectual merits – Evolution or descent with modification refers to the passing on to the next generation of a tool kit, with some tools being potentially modified or new. New tools are thought to be developed from copies of existing tools, through modification and optimization for new functions. The two extreme mechanisms to broaden the size of the toolbox is duplicating the entire set, that is whole genome duplication, or acquiring a set from another species via genome merger. We sampled populations of P. pyriforme throughout much of its North American range. We demonstrated that the combination of traits thought to define this species, was in fact shared by seven lineages. Three of these are the outcome of interspecific hybridization, a mechanism once thought to be negligeable in mosses or bryophytes. Sorting the genes of these hybrids into two or more sets to identify the putative parental species revealed that some parents are yet unknown, pointing at even more hidden diversity with this species complex in North America. 

Whole genome duplication is likely a widely underestimated mechanism in mosses. Its consequences on gene evolution are thought to emerge after a lag period. We induced genome duplication in a moss and examined, how the expression of its genes changed in this first generation. We demonstrated for the first time in mosses that such event immediately impacts gene expression, on the scale of at least 11% of genes affected. While the mechanisms underlying these shifts are unknown for now, they do highlight the significance of whole genome duplication in altering the targets of natural selection, and hence in triggering evolution, in mosses, and plants in general. Our project produced methods advancements for the analysis of DNA sequences in species with duplicated genomes. These advancements reduce per-sample costs and make data analysis more efficient, allowing us to address research questions that were not feasible or tractable before.  

Broader impacts – This project provided critical professional development to one junior research associate, who now holds a tenure track position at a liberal arts college. Our former associate acquired critical skills in phylogenetic analysis, in processing data of gene expression and in assembling and annotating genomes, all skills that will support pursuing a successful career and mentoring the next generation of students in STEM. The project funded a research technician, who wrote a first-author publication on improving methods in DNA sequencing and is now managing a lab at a major genomics facility. Three undergraduate students, all of whom identify as members of underrepresented minority groups in STEM, worked on the project. The undergradautes gained skills in tissue culture, DNA extraction, and bioinformatics. The grant allowed them to travel to a national botany conference to present their biodiversity research, greatly expanding their understanding of the importance of communication in science. Finally, the project provided opportunities to engage the public through a nation-wide citizen science initiative via iNaturalist which both enhanced awareness of often-hidden moss biodiversity and allowed us to acquire samples during the pandemic.

Last Modified: 06/25/2024
Modified by: Matthew G Johnson