From methylome to phenotype: a study on the effects of a multigenerational exposure to gamma radiation in Arabidopsis thaliana

Abstract

The goal of this PhD was to study if exposure to gamma radiation in multiple consecutive generations leads to long-term adaptive responses in Arabidopsis thaliana and to determine whether epigenetic mechanisms are involved in such adaptations across generations. Phenotypically, we observed that both vegetative and reproductive development were already altered in the first generation, but also that these changes intensified after additional exposures in subsequent generations. Plants had more leaves, larger rosettes, higher stems and heavier seeds after a third exposure to gamma radiation. Multiple exposures to radiation affected cell wall metabolism and antioxidative pathways as well: higher enzyme activities and gene transcript levels were present in plants that experienced radiation stress for the second time. The higher level of oxidative stress and DNA repair in drm1drm2cmt3 mutants indicated the importance of DNA methylation in the gamma stress response. This was further supported by the epigenetic sequencing results; genes with functions in cell wall metabolism, general stress, oxidative stress, terpenoid synthesis, etc… were differentially methylated in the progeny of gamma stressed plants. In conclusion, we have demonstrated that multigenerational exposure to gamma radiation leads to adaptive responses across generations in A. thaliana, that modification of the cell wall is key in this response and that these multigenerational adaptations are accompanied by DNA methylation changes in functional genes, especially after a second exposure.