Do plants adapt to chronic low-dose gamma exposure? A mechanistic study comparing plants exposed under field and lab conditions on (epi) genetic, biochemical and population level.

Laanen Paulus

Promoter

Cuypers Ann, (UHasselt), ann.cuypers@uhasselt.be

SCK•CEN Mentor

Horemans Nele
nele.horemans@sckcen.be
+32 14 33 21 15

SCK•CEN Co-mentor

Saenen Eline
eline.saenen@sckcen.be
+32 14 33 88 11

Expert group

Biosphere Impact Studies

PhD started

2018-10-01

Short project description

All living organisms are daily exposed to ionizing radiation coming from natural sources such as cosmic radiation and naturally occurring radionuclides. However, due to anthropogenic activities exposure to radionuclides and radiation can be increased. A comparison between toxicity data of organisms chronically exposed to radiation in Chernobyl contaminated area with those under lab and controlled field conditions showed that under field conditions species were about eight fold more sensitive leading to concerns if existing risk assessments based on lab data were sufficient (Garnier-Laplace et al. 2013). Different confounding factors were said to possibly contribute to this discrepancy with the ability of organisms to adapt to chronic enhanced radiation levels or more prominent the lack of adaptation being one of them. Within the scientific literature there is an active debate on whether organisms actually have the ability to adapt when chronically exposed to enhanced radiation levels and radionuclides (Moller and Mousseau 2016; Kovalchuk et al. 2004; Galván et al. 2014; Boubriak et al. 2016). For plants, being sessile organisms not able to escape enhanced levels of radiation this is of particular importance. As such a pilot study on soybean seedlings collected in Chernobyl exclusion zone showed higher levels of DNA damage correlated with the radiation gradient but the recovery of DNA damage was faster in the more radio-contaminated samples (Georgieva et al. 2017). Also Boubriak et al. (2008) reported on an enhanced DNA repair mechanism for birch pollen and primrose seed embryos found in contaminated areas of Chernobyl. From our own lab experiments comparing plants with one or two generation of exposure to radiation exposure, plants exposed for two generations induced a less prominent response (e.g. lower induction of antioxidative and DNA repair mechanisms) when challenged with additional radiation exposures (van de Walle et al. 2016). Although this needs further proof it was explained as the plants after two generations being more adapted towards the radiation than those exposed only for one generation. For Lemna minor on the other hand we found a dose rate dependent shift in the response that indicated adaptation of the plants only present at low levels of radiation (Van Hoeck et al. 2017). Challenging plants with radiation can also lead to an increased micro-evolution that on its turn can lead to the appearance of rare mutations, an increase in genetic and epigenetic polymorphism in the populations and eventually to a loss of the species balance within the ecosystem (Boubriak et al. 2016).

In conclusion plant populations seem to survive exposure to low doses of chronic irradiation but it is not clear whether this is accompanied with an adaptive response or local increased micro-evolution. Therefore to increase mechanistic understanding of adaptation of plants to low-dose radiation and safeguard ecosystem functioning it is stressed that further in depth genetic, epigenetic and phenotypic studies are needed

Objective

The main objective of this project is to study possible cellular and molecular (genetic/epigenetic) changes underpinning the adaptive responses of plants exposed to low doses of gamma radiation in lab and field conditions. This objective will be realised by providing an answer to the following research questions:

(i) Do plants expose adaptive responses when exposed for many generations to low dose of gamma radiation making them more resistant/sensitive towards additional new exposures.

(ii) Are molecular (epi)genetic markers present that mechanistically underpin the adaptive response.

(iii) Does exposure to chronic low dose radiation lead to enhanced genetic variation and population dynamics.

To find an answer on these research questions we will use both reproductive and cloning plants with a different radiation history and study their possible adaptive response. In-depth genetic and epigenetic analysis of these plants will be performed in order to link changes in the (epi)genome to the adaptive response. We will use three different plant species within this project: (1) Arabidopsis thalina (WP1) (2) Lemna minor (WP2) (3) Taraxacum officinale (common dandelion) (WP3) with different radiation background