Acclimation und adaptation in Arabidopsis arenosa

Project title: Disentangling evolutionary adaptation from transient acclimation to alpine environments in Arabidopsis arenosa Contents: The capability of plants to respond to altered environmental factors enables them to colonise new habitats. Such responses involve short-term adjustments in form and function, termed "acclimation", but also genetically fixed "adaptations" acquired through evolution, and can lead to the formations of new "ecotypes". These are locally adapted populations that can still interbreed. In this project, the sand rock- cress, Arabidopsis arenosa, will be used to elucidate the contribution of acclimation and adaptation in determining the traits that define the alpine ecotype of this plant. Research questions: 1) What are the structural, physiological and metabolic traits that define the alpine phenotype of A. arenosa? 2) Do these traits reflect transient acclimation to alpine environments and / or are they results of evolutionary adaptation, leading to the formation of distinct alpine ecotypes? Methods: Eight pairs of alpine and lowland A. arenosa populations from three geographically distant mountain ranges will be reciprocally transplanted into four common gardens. The effects of the altered environmental conditions will be assessed through in-depth studies of plant structure and function, including state-of-the-art "metabolite profiling". Novelty and innovation: A unique set of alpine A. arenosa populations will be used, which evolved in parallel from their respective lowland counterparts. These populations have already been genetically characterised by a collaborator. The available genome data will be integrated with the results gained in this project using bioinformatics techniques. In this way, it will be possible to elucidate the molecular basis of the adaptation to the alpine environment. This is important to understand how plants react to their environment, which is also relevant to research into climate change.

A clear understanding of how plant lineages adapt to divergent climatic conditions is required to predict the long-term impacts of climate change on biodiversity and agricultural production. The capability to respond to their environment also enables plants to colonise new habitats. Such responses can lead to the formation of new "ecotypes", involving short-term adjustments in form and function, termed "acclimation", and genetically fixed "adaptations" acquired through evolution. We used the sand rock-cress, Arabidopsis arenosa an outstanding model for investigating adaptations driven by environmental factors such as temperature, light intensity, precipitation and snow coverage to study acclimations and adaptations shaping alpine populations. The project aimed at a) addressing anatomical, physiological and metabolic traits that define alpine populations and b) investigating if these traits reflect transient acclimation to alpine environments and/or evolutionary adaptation. A set of alpine A. arenosa populations was used, which had evolved in parallel from their respective foothill counterparts. Eight alpine and foothill populations each, originating from the Eastern Alps (Austria), the Carpathian Mountains (Romania) and the Tatra mountains (Slovakia), were reciprocally transplanted into four common gardens. Eco-physiological assessment of plant performance (leaf anatomy and physiology, photosynthesis), "omics" analysis of leaves (untargeted metabolite profiling, genomics, re-analysis of transcriptome data) and targeted chromatographic techniques (photosynthetic pigments, cuticular waxes) were integrated with available genome data using bioinformatics techniques. Foothill and alpine populations exhibited similar adaptive responses to the different elevations regarding survival, flowering, stem height and accumulation of above-ground biomass, whereas rosette size, number of leaves, stems and flowers reflected their geographic origin. Parallel adaptation was likely caused by differential selective pressure at low- versus high-elevation in combination with lack or limited gene flow between foothill and alpine populations. These results showed that foothill and alpine populations can be assigned to two distinct ecotypes. Adaptive traits included a dynamic adjustment of freezing resistance. The alpine ecotype was better adapted to low temperatures, had thicker leaves and fewer trichomes (leaf hairs), and leaves differed regarding leaf minimum conductance, water saturation deficit and composition of cuticular waxes. The function of the cuticle this is a protective waxy film covering the outermost layer (the epidermis) of leaves differed between the two ecotypes, with differences in genetic background, transcriptional regulation and biochemical composition, including its contents of fatty alcohols. The project involved full-time employment of 2 postdoctoral scientists, and training of 1 Doctoral student, 2 Master, 3 Diploma and 2 Bachelor students. Project data were presented at national and international conferences and published in scientific journals (3 papers so far). In summary, by enhancing our understanding of how climatic factors drive the formation of ecotypes, the project contributed to basic science, with potential downstream impacts on agriculture and conservation.