Genetic processes in Scots pine (Pinus sylvestris L.) in the Chernobyl exclusion zone
Final Report Abstract
We analyzed the long-term impacts of high radiation caused by the Chernobyl nuclear accident on the genetics of forest ecosystems taking pines (Pinus sylvestris) as an example. Complex responses and reactions of pine populations to both acute and chronic radiation were observed. We were able to identify mutations, modified expression patterns of genes involved in stress response, genome methylation, and selection as main factors reacting to the extreme environmental change created by the nuclear accident. We observed genetic structures in a pine plantation exposed to acute radiation during the accident, followed by chronic radiation, pine plantations established on highly contaminated soils after the accident, and reference plantations as controls of the same age and origin as the exposed populations. Somatic mutations were assessed by the analysis of DNA from four branches with different orientation of sample trees. Variation within trees was regarded as indication for a mutation; analyses of putative mutations were repeated or confirmed by sequencing. We observed mutations at highly polymorphic, non-coding microsatellites (or simple sequences repeats) in contaminated populations, but not in the controls. However, mutation frequencies within these regions were low and the observed difference between contaminated and control populations were not significant. The identification of higher mutation rates at anonymous AFLP (amplified fragment length polymorphism) fingerprints was unexpected. Mutation rates were threefold increased and significantly higher in populations exposed to chronic radiation in comparison to controls at this marker type. This result is among the first to use AFLPs for the analysis of mutation rates, it suggests genome-wide DNA damage caused by high radiation. Mutations and the expression profile of the genes catalase and glutathione peroxidase, which might be involved in protection of the cell from the damaging effects of hydrogen peroxide accumulation caused by radiation, were analysed in five trees from each of the different populations. Somatic mutations were observed at the catalase, but not at the glutathione peroxidase gene in irradiated trees. Glutathione peroxidase was slightly down regulated, but catalase strongly, sixteen-fold upregulated in exposed trees in comparisons to the controls. The results points towards modifications of gene regulation in response to radiation stress. Protection of DNA and putative transcriptional silencing of genes was studied using methylation-sensitive AFLP analyses. A considerably higher frequency of methylated and hemimethylated fragments in irradiated trees in comparison to controls indicates that the adaptive response of pines to high radiation involves irreversible DNA methylation. Selection was assessed by comparing genetic structures at AFLPs between pine trees showing strong signs of damage in radioactively exposed sites, trees showing no or minor damage, and control trees in non-exposed sites. Genetic structures of irradiated trees with different stress symptoms were similar, but a high proportion of gene loci revealed strong differences between the groups of exposed trees in comparison to the control. Fifteen out of 222 investigated loci (approximately 6%) were identified as outliers not fitting neutral expectations. Thus, these loci are assumed to be under selection. The most remarkable result of this study is the identification of selection as a main evolutionary factor contribution to the adaptation of pines to high radiation. We plan to inform the media about the outcome of the project and in particular the selective response of pines due as an example of adaptation to extreme and rapid environmental change after results have been accepted for publication in scientific journals.
Publications
- Genetic processes in Scots pine (Pinus sylvestris L.) in the Chernobyl exclusion zone. PhD thesis
Oleksandra Kuchma
- Forest Ecosystem Genomics and Adaptation, 9 – 11 June 2010, San Lorenzo de El Escorial (Madrid), Spain; “Genetic processes in Scots pine (Pinus sylvestris L.) in the Chernobyl exclusion zone”
- Forstwissenschaftliche Tagung 2010, 22 – 24 September 2010, Georg-August-Universität Göttingen, Germany; „Molekulare Aspekte zur Anpassung von Kiefern (Pinus sylvestris L.) an radioaktive Strahlung“
