The overall objective of this thesis is to assess the epigenetic impact on plant plasticity. We have investigated how environmental perceptions of plants can lead to alterations and responses that potentially cross generations.
We assessed the impact of the major epigenetic regulator, DNA methylations, on the defence compounds glucosinolates. This was facilitated by the availability of epigenetic Recombinant Inbred Lines, an Arabidopsis thaliana population that varies in DNA methylations and little in DNA.
Methylation of specific genomic regions correlated with the mean abundance of different glucosinolate compounds and furthermore, methylations affected the variance of glucosinolates. This suggests that variance of the defence compounds is a controlled trait. By comparing our data to glucosinolate studies in populations with genetic variation, we could assess the relative contribution
of epigenetics verses genetics on these compounds. We show an epigenetic impact on glucosinolates, yet not as big as genetic impact. As such, genetic variation must be the major driver of the evolution of glucosinolates.
We investigated one glucosinolate outlier in the population that did not match the Gaussian distribution of the epigenetic Recombinant Inbred Lines, which we hypothesized to have genetic causality for its compound levels rather than epigenetic. By testing for Mendelian segregation and genome sequencing, we identified the movement of a transposable element into the gene of a glucosinolate transporter. RNA sequencing revealed a tissue specific transcriptomic profiles, likely explained by feedback to the impaired transport. Transposable element movement in the population of epigenetic Recombinant Inbred Lines has previously been shown, but so far, transpositions had
been shown to originate from the early steps in the population establishment. Our story provides an example of a transposition that happened in the later steps of the making of lines.
Bet hedging is an evolutionary strategy of deliberate variance as a means to overcome unpredictable future stress at the expense of momentary fitness. We assessed bet hedging strategies in Arabidopsis thaliana wild type by assessing 22 traits in offspring. We tested progeny trait variation in relation to the position of the silique on the bolt of the parental plant. This allowed us to study the
impact of the timing of seed production on traits in offspring seeds and plants. To test for strategies for transgenerational propagation of increased resistance, we exposed parental plants to herbivory at different developmental stages. We show that progeny vary for many traits in relation to the specific silique position on parent and this variation is differentially affected by herbivore stress. Furthermore, herbivore stress in the parental generation correlated with increased resistance to both abiotic and biotic stress in following generation. Increased resistance to relatively abiotic and biotic stress propagated to different silique positions.
These findings suggest that plants are able to propagate increased resistance to part of their offspring and then shift to a bet hedging strategy for the remaining progeny. Thus, plants can change their strategy for transgenerational priming during their lifetime.