Collaborative Research: Genome structure and adaptive evolution in peatmosses (Sphagnum): ecosystem engineers

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Peatmosses comprise a diverse group of plants with over 300 species distributed throughout the world. In northern parts of the Northern Hemisphere, they dominate wetlands and form extensive peatlands that harbor a broad diversity of microbes, other plants, and animals. Because of the build-up of peat (partially decomposed plant material), these peatlands have profound impacts on regional patterns of water movement, and the global cycling of atmospheric nitrogen, carbon dioxide, and methane. It is estimated that almost one third of the earth's soil carbon is bound up in peatlands even though these habitats account for only about 10% of the land surface area. The goals of this research are to use peatmosses as a model to better understand the connections between DNA sequence variation, plant traits, and ecological function. This research provides a unique opportunity to connect gene composition and variation to the plant traits encoded by those genes, and investigate how these plant traits affect ecosystem function. Undergraduates, graduate students and post-doctoral researchers will be trained in diverse genomic, evolutionary, computational, and ecological methods and analysis, including laboratory exchanges among the collaborating institutions. Results will be disseminated broadly to the public via field courses and an illustrated publically accessible, online database about peatmosses. This research integrates broad-level phylogenetics, common garden experiments of a widely-distributed Sphagnum species, and genus-wide comparative genomic studies to understand how adaptive processes occurring within species scale up to and explain diversification of the genus on a worldwide scale. Whole genome DNA sequences will be assembled for 96 Sphagnum species representing the worldwide range of the genus. These data will then be used to reconstruct phylogenetic relationships among species and assess genus-wide genomic variation. Analyses of these data will then test for correlations among phylogenetic patterns, distributional range, ecological breadth, and variation in ecologically important phenotypic traits. Plants of Sphagnum magellanicum, which occurs from arctic to tropical regions, will be collected across a latitudinal gradient and grown under experimental conditions to assess photosynthetic responses to environmental factors including day length and temperature, and population differentiation in physiological response. Gene expression responses in experimental plants will be measured using RNA sequencing to better understand the genetic basis of local physiological adaptation. Whole genome DNA sequences of different S. magellanicum populations will be assembled to assess variation in gene content within a single species (Pan genome structure). Comparing these population-level data with whole genome sequence data from species spanning the Sphagnum genus will identify how many of these genes are shared with other peatmoss species. One specific prediction these data will be used to test is whether inducible physiological responses in tropical plants of a widespread species have become fixed and constitutive in tropical Sphagnum species.