Exploring the epigenetic mechanisms of stress adaptation in plants

In all organisms repetitive DNA elements called transposons or transposable elements (TEs) are found that may have the ability to move within the genome and insert into new chromosomal locations. Under normal conditions TEs are kept silent as active transposons are highly mutagenic and may cause undesired genomic rearrangements. It is known that TEs can be activated under elevated temperatures. As such, the mechanisms of TE regulation are of importance to investigate in the light of global warming. Global climate change may lead to a temperature rise that is predicted to have dramatic impact on crop growth and productivity. In this project, the focus is on SUVR4, a histone lysine methyltransferase (HKMtase) of the model plant Arabidopsis thaliana, which is highly conserved in the plant kingdom. Our data indicates that the function of SUVR4 is repression of transposons through its H3K9 trimethylation activity, this action being dependent on a protein domain of SUVR4 called WIYLD. Genome wide analysis shows that SUVR4 is active only on certain transposon families and preliminary data suggests that SUVR4 is needed for resilencing of these TEs following heat stress.

Global climate change is predicted to lead to a temperature rise that will have a dramatic impact on crop growth and productivity. In the Nordic hemisphere higher temperatures during the winter months may result in insufficient cold treatment seriously af fecting budbreak and transition to/duration of flowering. Elevated temperatures may also activate transposable elements, leading to increased frequencies of mutations. To reduce these expected negative effects, we need a comprehensive understanding of the genetics underlying transition to flowering, as well as the mechanisms of suppression of TE activity. This project proposal is focusing on the function of the histone methyltransferase (HKMtase) SUVR4, highly conserved in the plant kingdom, for which cur rent data suggest involvement both in control of flowering time and TE repression. The majority of TEs are kept silent through complex regulatory mechanisms including DNA methylation, repressive histone modifications and RNA interference. SUVR4 of the m odel plant Arabidopsis thaliana repress transposons through its H3K9me3 activity. In the proposed post.doc. project my hypothesis is that SUVR4 is involved in resetting of transposon repression following heat stress. I seek to clarify the position of SUVR 4 in the pathways of TE repression involving the epigenetic regulator MOM1, the histone H2B deubiquitination enzyme UBP26 and the plant-specific DNA-dependent RNA polymerases PolIV and PolV using mutant analyses, genetic crosses, and Chromatin Immuno Prec ipitation. SUVR4 is also affecting flowering time, either through its H3K9 di- or trimethylating activity, and is therefore a candidate HKMTase for these chromatin marks in the epigenetic control of FLOWERING LOCUS C (FLC), the main regulator of flowerin g time in Arabidopsis. Through whole-genome ChIP-seq and analysis of crosses to flowering time mutants my project will clarify the cross-talk of SUVR4 with other histone modifying enzymes in flowering time pathways.