PhD Thesis: Tracing Molecular Patterns of Adaptation in Arctic Brassicaceae

• Main Author: Birkeland, Siri
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2020
• Subjects: Cochlearia groenlandica
• Online Access: https://doi.org/10.5061/dryad.7pvmcvdqx

Extreme environments can function as natural laboratories for studying how different organisms adapt to similar selection pressures at the genetic level. This thesis explores how three Arctic plant species independently adapted to some of the coldest biomes on Earth, and how they evolved similar suites of adaptations to extremes in light and temperature. It addresses fundamental questions in plant evolutionary biology, such as the extent to which adaptation follows the same genetic trajectories in different species, and the genetic basis for plant adaptation to extreme environments. The thesis has two main objectives that are addressed through three papers ( Papers I-III ): 1) estimate the degree of adaptive molecular convergence in the three Arctic Brassicaceae Cardamine bellidifolia , Cochlearia groenlandica , and Draba nivalis , and 2) identify putative molecular adaptations to the Arctic environment in the same three species. Approach. The first two papers examine the degree of evolutionary repeatability in how C. bellidifolia , C. groenlandica , and D. nivalis adapted to the Arctic environment at the genetic level ( objective 1 ). In Paper I , we estimated molecular convergence at the level of codons, genes, and functional pathways, by comparing genome-wide patterns of positive selection and identifying convergent substitutions in the three species. In Paper II , we conducted a time series experiment to examine the transcriptional responses of the Arctic Brassicaceae to low temperatures, and to identify potential convergent expression patterns in cold response. All three papers identify putative molecular adaptations to extremes in light and temperature ( objective 2 ). In Paper I , we identified candidate genes for adaptation to the Arctic environment by searching for positively selected genes associated with abiotic stresses common in the Arctic. In Paper II , we explored the molecular basis of cold tolerance in Arctic Brassicaceae, and described how their cold-induced transcriptomes differ from that of ...