Contribution of epigenetic processes to the induction of long-term effects and adaptive responses of plants exposed to low-dose radiation (Research)
A background of ionising radiation is generally present in the environment coming from cosmic sources or natural occurring radioactive materials. However, the use of different radionuclides for energy production, medicine or research has led to potential local increases of radioactive material in the environment and hence to an increased risk of exposure of wildlife residing in these areas . Although, in recent years considerable progress is made to develop a framework for the ecological risk assessment of exposure to radioactive substances major challenges still remain (Copplestone et al. 2004; Garnier-Laplace et al. 2006). In particular research studying long-term and trans-generational effects of organisms exposed to environmental relevant radiation dose rates in combination with knowledge on the underlying mechanisms is still needed (Hinton et al. 2013). It is the objective of this PhD project to study the long-term impact of low dose gamma radiation to plants (within and across generations) and to reveal underlying mechanism at a cellular level. Ionising radiation can induce genotoxic effects by interacting with DNA either directly or indirectly. In addition to inducing DNA damage, oxidative stress coming from an enhanced ROS production can lead to alterations in proteins and lipids. Damage to DNA can manifest itself as single and double strand breaks, oxidative changes and DNA lesions. Organisms can react upon exposure to ionising radiation by inducing different stress and/or DNA repair mechanisms hence, minimising adverse effects and even inducing adaptive responses (Esnault et al. 2010). Epigenetic changes include post-translational modifications of histones and/or silencing or enhancing mechanisms such as DNA methylation and miRNA's and siRNA's. These modifications can result in a different expression of proteins without directly changing the DNA sequence. The alterations can, for example, change the chromosomal structure. A number of studies have shown that these epigenetic DNA changes and histone modifications play a key role in gene expression and in plant development of plants under stress (Chinnusamy and Zhu 2009; Bruce et al. 2007). Most of these stress-induced modification are reversed once the stress is relieved, however, some may be stable leading to acclimation or adaptive responses that can be passed on to the next generation. Indications for the contribution of epigenetic changes in the stress response of plants exposed to radiation to date come mainly from studies in Chernobyl where a general dose-rate dependent enhancement of the methylation degree of the genome was found in both Pinus trees and Arabidopsis plants (Kovalchuk et al. 2003; Kovalchuk et al. 2004). In these studies the observed epigenetic changes were linked to the adaptation of the plants to better tolerate chronic radiation exposure. However, adaptive responses to any kind of stress might also have a negative impact on the yield of crops by preventing plants to grow to their full potential impacting the use of adapted plant seeds by breeders and farmers. It is the hypothesis of this study that gamma radiation induces long-term effects in plants that can alter the plant's radiosensitivity and that epigenetic changes can lead to adaptive responses over several generations.
Period of project
01 October 2013 - 30 September 2017