@article{FriedrichOberkoflerTrindadeetal.2021, author = {Friedrich, Thomas and Oberkofler, Vicky and Trindade, In{\^e}s and Altmann, Simone and Brzezinka, Krzysztof and L{\"a}mke, J{\"o}rn S. and Gorka, Michal and Kappel, Christian and Sokolowska, Ewelina and Skirycz, Aleksandra and Graf, Alexander and B{\"a}urle, Isabel}, title = {Heteromeric HSFA2/HSFA3 complexes drive transcriptional memory after heat stress in Arabidopsis}, series = {Nature Communications}, volume = {12}, journal = {Nature Communications}, number = {1}, publisher = {Nature Publishing Group UK}, address = {[London]}, issn = {2041-1723}, doi = {10.1038/s41467-021-23786-6}, pages = {15}, year = {2021}, abstract = {Adaptive plasticity in stress responses is a key element of plant survival strategies. For instance, moderate heat stress (HS) primes a plant to acquire thermotolerance, which allows subsequent survival of more severe HS conditions. Acquired thermotolerance is actively maintained over several days (HS memory) and involves the sustained induction of memory-related genes. Here we show that FORGETTER3/ HEAT SHOCK TRANSCRIPTION FACTOR A3 (FGT3/HSFA3) is specifically required for physiological HS memory and maintaining high memory-gene expression during the days following a HS exposure. HSFA3 mediates HS memory by direct transcriptional activation of memory-related genes after return to normal growth temperatures. HSFA3 binds HSFA2, and in vivo both proteins form heteromeric complexes with additional HSFs. Our results indicate that only complexes containing both HSFA2 and HSFA3 efficiently promote transcriptional memory by positively influencing histone H3 lysine 4 (H3K4) hyper-methylation. In summary, our work defines the major HSF complex controlling transcriptional memory and elucidates the in vivo dynamics of HSF complexes during somatic stress memory. Moderate heat stress primes plants to acquire tolerance to subsequent, more severe heat stress. Here the authors show that the HSFA3 transcription factor forms a heteromeric complex with HSFA2 to sustain activated transcription of genes required for acquired thermotolerance by promoting H3K4 hyper-methylation.}, language = {en} } @phdthesis{Oberkofler2022, author = {Oberkofler, Vicky}, title = {Molecular basis of HS memory in Arabidopsis thaliana}, doi = {10.25932/publishup-56954}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-569544}, school = {Universit{\"a}t Potsdam}, pages = {181}, year = {2022}, abstract = {Plants can be primed to survive the exposure to a severe heat stress (HS) by prior exposure to a mild HS. The information about the priming stimulus is maintained by the plant for several days. This maintenance of acquired thermotolerance, or HS memory, is genetically separable from the acquisition of thermotolerance itself and several specific regulatory factors have been identified in recent years. On the molecular level, HS memory correlates with two types of transcriptional memory, type I and type II, that characterize a partially overlapping subset of HS-inducible genes. Type I transcriptional memory or sustained induction refers to the sustained transcriptional induction above non-stressed expression levels of a gene for a prolonged time period after the end of the stress exposure. Type II transcriptional memory refers to an altered transcriptional response of a gene after repeated exposure to a stress of similar duration and intensity. In particular, enhanced re-induction refers to a transcriptional pattern in which a gene is induced to a significantly higher degree after the second stress exposure than after the first. This thesis describes the functional characterization of a novel positive transcriptional regulator of type I transcriptional memory, the heat shock transcription factor HSFA3, and compares it to HSFA2, a known positive regulator of type I and type II transcriptional memory. It investigates type I transcriptional memory and its dependence on HSFA2 and HSFA3 for the first time on a genome-wide level, and gives insight on the formation of heteromeric HSF complexes in response to HS. This thesis confirms the tight correlation between transcriptional memory and H3K4 hyper-methylation, reported here in a case study that aimed to reduce H3K4 hyper-methylation of the type II transcriptional memory gene APX2 by CRISPR/dCas9-mediated epigenome editing. Finally, this thesis gives insight into the requirements for a heat shock transcription factor to function as a positive regulator of transcriptional memory, both in terms of its expression profile and protein abundance after HS and the contribution of individual functional domains. In summary, this thesis contributes to a more detailed understanding of the molecular processes underlying transcriptional memory and therefore HS memory, in Arabidopsis thaliana.}, language = {en} } @article{KappelFriedrichOberkofleretal.2023, author = {Kappel, Christian and Friedrich, Thomas and Oberkofler, Vicky and Jiang, Li and Crawford, Tim and Lenhard, Michael and B{\"a}urle, Isabel}, title = {Genomic and epigenomic determinants of heat stress-induced transcriptional memory in Arabidopsis}, series = {Genome biology : biology for the post-genomic era}, volume = {24}, journal = {Genome biology : biology for the post-genomic era}, number = {1}, publisher = {BioMed Central}, address = {London}, issn = {1474-760X}, doi = {10.1186/s13059-023-02970-5}, pages = {23}, year = {2023}, abstract = {Background Transcriptional regulation is a key aspect of environmental stress responses. Heat stress induces transcriptional memory, i.e., sustained induction or enhanced re-induction of transcription, that allows plants to respond more efficiently to a recurrent HS. In light of more frequent temperature extremes due to climate change, improving heat tolerance in crop plants is an important breeding goal. However, not all heat stress-inducible genes show transcriptional memory, and it is unclear what distinguishes memory from non-memory genes. To address this issue and understand the genome and epigenome architecture of transcriptional memory after heat stress, we identify the global target genes of two key memory heat shock transcription factors, HSFA2 and HSFA3, using time course ChIP-seq. Results HSFA2 and HSFA3 show near identical binding patterns. In vitro and in vivo binding strength is highly correlated, indicating the importance of DNA sequence elements. In particular, genes with transcriptional memory are strongly enriched for a tripartite heat shock element, and are hallmarked by several features: low expression levels in the absence of heat stress, accessible chromatin environment, and heat stress-induced enrichment of H3K4 trimethylation. These results are confirmed by an orthogonal transcriptomic data set using both de novo clustering and an established definition of memory genes. Conclusions Our findings provide an integrated view of HSF-dependent transcriptional memory and shed light on its sequence and chromatin determinants, enabling the prediction and engineering of genes with transcriptional memory behavior.}, language = {en} } @article{OberkoflerBaeurle2022, author = {Oberkofler, Vicky and B{\"a}urle, Isabel}, title = {Inducible epigenome editing probes for the role of histone H3K4 methylation in Arabidopsis heat stress memory}, series = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants}, volume = {189}, journal = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants}, number = {2}, publisher = {Oxford University Press}, address = {Oxford}, issn = {0032-0889}, doi = {10.1093/plphys/kiac113}, pages = {703 -- 714}, year = {2022}, abstract = {A temperature-inducible epigenome editing system to knock down histone methylation can be used to study the role of histone H3K4 methylation during heat stress memory in Arabidopsis.
Histone modifications play a crucial role in the integration of environmental signals to mediate gene expression outcomes. However, genetic and pharmacological interference often causes pleiotropic effects, creating the urgent need for methods that allow locus-specific manipulation of histone modifications, preferably in an inducible manner. Here, we report an inducible system for epigenome editing in Arabidopsis (Arabidopsis thaliana) using a heat-inducible dCas9 to target a JUMONJI (JMJ) histone H3 lysine 4 (H3K4) demethylase domain to a locus of interest. As a model locus, we target the ASCORBATE PEROXIDASE2 (APX2) gene that shows transcriptional memory after heat stress (HS), correlating with H3K4 hyper-methylation. We show that dCas9-JMJ is targeted in a HS-dependent manner to APX2 and that the HS-induced overaccumulation of H3K4 trimethylation (H3K4me3) decreases when dCas9-JMJ binds to the locus. This results in reduced HS-mediated transcriptional memory at the APX2 locus. Targeting an enzymatically inactive JMJ protein in an analogous manner affected transcriptional memory less than the active JMJ protein; however, we still observed a decrease in H3K4 methylation levels. Thus, the inducible targeting of dCas9-JMJ to APX2 was effective in reducing H3K4 methylation levels. As the effect was not fully dependent on enzyme activity of the eraser domain, the dCas9-JMJ fusion protein may act in part independently of its demethylase activity. This underlines the need for caution in the design and interpretation of epigenome editing studies. We expect our versatile inducible epigenome editing system to be especially useful for studying temporal dynamics of chromatin modifications.}, language = {en} } @article{OberkoflerPratxBaeurle2021, author = {Oberkofler, Vicky and Pratx, Loris and B{\"a}urle, Isabel}, title = {Epigenetic regulation of abiotic stress memory}, series = {Current opinion in plant biology}, volume = {61}, journal = {Current opinion in plant biology}, publisher = {Elsevier}, address = {London}, issn = {1369-5266}, doi = {10.1016/j.pbi.2021.102007}, pages = {7}, year = {2021}, abstract = {As sessile organisms, plants have evolved sophisticated ways to constantly gauge and adapt to changing environmental conditions including extremes that may be harmful to their growth and development and are thus perceived as stress. In nature, stressful events are often chronic or recurring and thus an initial stress may prime a plant to respond more efficiently to a subsequent stress event. An epigenetic basis of such stress memory was long postulated and in recent years it has been shown that this is indeed the case. High temperature stress has proven an excellent system to unpick the molecular basis of somatic stress memory, which includes histone modifications and nucleosome occupancy. This review discusses recent findings and pinpoints open questions in the field.}, language = {en} }