TY - JOUR A1 - Skłodowski, Kamil A1 - Riedelsberger, Janin A1 - Raddatz, Natalia A1 - Riadi, Gonzalo A1 - Caballero, Julio A1 - Chérel, Isabelle A1 - Schulze, Waltraud A1 - Graf, Alexander A1 - Dreyer, Ingo T1 - The receptor-like pseudokinase MRH1 interacts with the voltage-gated potassium channel AKT2 JF - Scientific reports N2 - The potassium channel AKT2 plays important roles in phloem loading and unloading. It can operate as inward-rectifying channel that allows H+-ATPase-energized K+ uptake. Moreover, through reversible post-translational modifications it can also function as an open, K+-selective channel, which taps a ‘potassium battery’, providing additional energy for transmembrane transport processes. Knowledge about proteins involved in the regulation of the operational mode of AKT2 is very limited. Here, we employed a large-scale yeast two-hybrid screen in combination with fluorescence tagging and null-allele mutant phenotype analysis and identified the plasma membrane localized receptor-like kinase MRH1/MDIS2 (AT4G18640) as interaction partner of AKT2. The phenotype of the mrh1-1 knockout plant mirrors that of akt2 knockout plants in energy limiting conditions. Electrophysiological analyses showed that MRH1/MDIS2 failed to exert any functional regulation on AKT2. Using structural protein modeling approaches, we instead gathered evidence that the putative kinase domain of MRH1/MDIS2 lacks essential sites that are indispensable for a functional kinase suggesting that MRH1/MDIS2 is a pseudokinase. We propose that MRH1/MDIS2 and AKT2 are likely parts of a bigger protein complex. MRH1 might help to recruit other, so far unknown partners, which post-translationally regulate AKT2. Additionally, MRH1 might be involved in the recognition of chemical signals. Y1 - 2017 U6 - https://doi.org/10.1038/srep44611 SN - 2045-2322 VL - 7 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Kabelitz, Tina A1 - Brzezinka, Krzysztof A1 - Friedrich, Thomas A1 - Gorka, Michal A1 - Graf, Alexander A1 - Kappel, Christian A1 - Bäurle, Isabel T1 - A JUMONJI Protein with E3 Ligase and Histone H3 Binding Activities Affects Transposon Silencing in Arabidopsis JF - Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants N2 - Transposable elements (TEs) make up a large proportion of eukaryotic genomes. As their mobilization creates genetic variation that threatens genome integrity, TEs are epigenetically silenced through several pathways, and this may spread to neighboring sequences. JUMONJI (JMJ) proteins can function as antisilencing factors and prevent silencing of genes next to TEs. Whether TE silencing is counterbalanced by the activity of antisilencing factors is still unclear. Here, we characterize JMJ24 as a regulator of TE silencing. We show that loss of JMJ24 results in increased silencing of the DNA transposon AtMu1c, while overexpression of JMJ24 reduces silencing. JMJ24 has a JumonjiC (JmjC) domain and two RING domains. JMJ24 autoubiquitinates in vitro, demonstrating E3 ligase activity of the RING domain(s). JMJ24-JmjC binds the N-terminal tail of histone H3, and full-length JMJ24 binds histone H3 in vivo. JMJ24 activity is anticorrelated with histone H3 Lys 9 dimethylation (H3K9me2) levels at AtMu1c. Double mutant analyses with epigenetic silencing mutants suggest that JMJ24 antagonizes histone H3K9me2 and requires H3K9 methyltransferases for its activity on AtMu1c. Genome-wide transcriptome analysis indicates that JMJ24 affects silencing at additional TEs. Our results suggest that the JmjC domain of JMJ24 has lost demethylase activity but has been retained as a binding domain for histone H3. This is in line with phylogenetic analyses indicating that JMJ24 (with the mutated JmjC domain) is widely conserved in angiosperms. Taken together, this study assigns a role in TE silencing to a conserved JmjC-domain protein with E3 ligase activity, but no demethylase activity. Y1 - 2016 U6 - https://doi.org/10.1104/pp.15.01688 SN - 0032-0889 SN - 1532-2548 VL - 171 SP - 344 EP - 358 PB - American Society of Plant Physiologists CY - Rockville ER - TY - JOUR A1 - Janowski, Marcin Andrzej A1 - Zoschke, Reimo A1 - Scharff, Lars B. A1 - Jaime, Silvia Martinez A1 - Ferrari, Camilla A1 - Proost, Sebastian A1 - Xiong, Jonathan Ng Wei A1 - Omranian, Nooshin A1 - Musialak-Lange, Magdalena A1 - Nikoloski, Zoran A1 - Graf, Alexander A1 - Schoettler, Mark Aurel A1 - Sampathkumar, Arun A1 - Vaid, Neha A1 - Mutwil, Marek T1 - AtRsgA from Arabidopsis thaliana is important for maturation of the small subunit of the chloroplast ribosome JF - The plant journal N2 - Plastid ribosomes are very similar in structure and function to the ribosomes of their bacterial ancestors. Since ribosome biogenesis is not thermodynamically favorable under biological conditions it requires the activity of many assembly factors. Here we have characterized a homolog of bacterial RsgA in Arabidopsis thaliana and show that it can complement the bacterial homolog. Functional characterization of a strong mutant in Arabidopsis revealed that the protein is essential for plant viability, while a weak mutant produced dwarf, chlorotic plants that incorporated immature pre-16S ribosomal RNA into translating ribosomes. Physiological analysis of the mutant plants revealed smaller, but more numerous, chloroplasts in the mesophyll cells, reduction of chlorophyll a and b, depletion of proplastids from the rib meristem and decreased photosynthetic electron transport rate and efficiency. Comparative RNA sequencing and proteomic analysis of the weak mutant and wild-type plants revealed that various biotic stress-related, transcriptional regulation and post-transcriptional modification pathways were repressed in the mutant. Intriguingly, while nuclear- and chloroplast-encoded photosynthesis-related proteins were less abundant in the mutant, the corresponding transcripts were increased, suggesting an elaborate compensatory mechanism, potentially via differentially active retrograde signaling pathways. To conclude, this study reveals a chloroplast ribosome assembly factor and outlines the transcriptomic and proteomic responses of the compensatory mechanism activated during decreased chloroplast function. Significance Statement AtRsgA is an assembly factor necessary for maturation of the small subunit of the chloroplast ribosome. Depletion of AtRsgA leads to dwarfed, chlorotic plants, a decrease of mature 16S rRNA and smaller, but more numerous, chloroplasts. Large-scale transcriptomic and proteomic analysis revealed that chloroplast-encoded and -targeted proteins were less abundant, while the corresponding transcripts were increased in the mutant. We analyze the transcriptional responses of several retrograde signaling pathways to suggest the mechanism underlying this compensatory response. KW - ribosome assembly KW - chloroplast ribosome KW - assembly factor KW - 30S subunit KW - RsgA KW - Arabidopsis thaliana Y1 - 2018 U6 - https://doi.org/10.1111/tpj.14040 SN - 0960-7412 SN - 1365-313X VL - 96 IS - 2 SP - 404 EP - 420 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Friedrich, Thomas A1 - Oberkofler, Vicky A1 - Trindade, Inês A1 - Altmann, Simone A1 - Brzezinka, Krzysztof A1 - Lämke, Jörn S. A1 - Gorka, Michal A1 - Kappel, Christian A1 - Sokolowska, Ewelina A1 - Skirycz, Aleksandra A1 - Graf, Alexander A1 - Bäurle, Isabel T1 - Heteromeric HSFA2/HSFA3 complexes drive transcriptional memory after heat stress in Arabidopsis JF - Nature Communications N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1038/s41467-021-23786-6 SN - 2041-1723 VL - 12 IS - 1 PB - Nature Publishing Group UK CY - [London] ER - TY - JOUR A1 - Comparot-Moss, Sylviane A1 - Koetting, Oliver A1 - Stettler, Michaela A1 - Edner, Christoph A1 - Graf, Alexander A1 - Weise, Sean E. A1 - Streb, Sebastian A1 - Lue, Wei-Ling A1 - MacLean, Daniel A1 - Mahlow, Sebastian A1 - Ritte, Gerhard A1 - Steup, Martin A1 - Chen, Jychian A1 - Zeeman, Samuel C. A1 - Smith, Alison M. T1 - A putative phosphatase, LSF1, is required for normal starch turnover in Arabidopsis leaves N2 - A putative phosphatase, LSF1 (for LIKE SEX4; previously PTPKIS2), is closely related in sequence and structure to STARCH-EXCESS4 (SEX4), an enzyme necessary for the removal of phosphate groups from starch polymers during starch degradation in Arabidopsis (Arabidopsis thaliana) leaves at night. We show that LSF1 is also required for starch degradation: lsf1 mutants, like sex4 mutants, have substantially more starch in their leaves than wild-type plants throughout the diurnal cycle. LSF1 is chloroplastic and is located on the surface of starch granules. lsf1 and sex4 mutants show similar, extensive changes relative to wild-type plants in the expression of sugar-sensitive genes. However, although LSF1 and SEX4 are probably both involved in the early stages of starch degradation, we show that LSF1 neither catalyzes the same reaction as SEX4 nor mediates a sequential step in the pathway. Evidence includes the contents and metabolism of phosphorylated glucans in the single mutants. The sex4 mutant accumulates soluble phospho- oligosaccharides undetectable in wild-type plants and is deficient in a starch granule-dephosphorylating activity present in wild-type plants. The lsf1 mutant displays neither of these phenotypes. The phenotype of the lsf1/sex4 double mutant also differs from that of both single mutants in several respects. We discuss the possible role of the LSF1 protein in starch degradation. Y1 - 2010 UR - http://www.plantphysiol.org/ U6 - https://doi.org/10.1104/pp.109.148981 SN - 0032-0889 ER - TY - JOUR A1 - Castellanos, Reynel Urrea A1 - Friedrich, Thomas A1 - Petrovic, Nevena A1 - Altmann, Simone A1 - Brzezinka, Krzysztof A1 - Gorka, Michal A1 - Graf, Alexander A1 - Bäurle, Isabel T1 - FORGETTER2 protein phosphatase and phospholipase D modulate heat stress memory in Arabidopsis JF - The plant journal N2 - Plants can mitigate environmental stress conditions through acclimation. In the case of fluctuating stress conditions such as high temperatures, maintaining a stress memory enables a more efficient response upon recurring stress. In a genetic screen forArabidopsis thalianamutants impaired in the memory of heat stress (HS) we have isolated theFORGETTER2(FGT2) gene, which encodes a type 2C protein phosphatase (PP2C) of the D-clade.Fgt2mutants acquire thermotolerance normally; however, they are defective in the memory of HS. FGT2 interacts with phospholipase D alpha 2 (PLD alpha 2), which is involved in the metabolism of membrane phospholipids and is also required for HS memory. In summary, we have uncovered a previously unknown component of HS memory and identified the FGT2 protein phosphatase and PLD alpha 2 as crucial players, suggesting that phosphatidic acid-dependent signaling or membrane composition dynamics underlie HS memory. KW - priming KW - protein phosphatase KW - stress memory KW - heat stress KW - Arabidopsis KW - thaliana Y1 - 2020 U6 - https://doi.org/10.1111/tpj.14927 SN - 0960-7412 SN - 1365-313X VL - 104 IS - 1 SP - 7 EP - 17 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Brzezinka, Krzysztof A1 - Altmann, Simone A1 - Czesnick, Hjördis A1 - Nicolas, Philippe A1 - Gorka, Michal A1 - Benke, Eileen A1 - Kabelitz, Tina A1 - Jähne, Felix A1 - Graf, Alexander A1 - Kappel, Christian A1 - Bäurle, Isabel T1 - Arabidopsis FORGETTER1 mediates stress-induced chromatin memory through nucleosome remodeling JF - eLife N2 - Plants as sessile organisms can adapt to environmental stress to mitigate its adverse effects. As part of such adaptation they maintain an active memory of heat stress for several days that promotes a more efficient response to recurring stress. We show that this heat stress memory requires the activity of the FORGETTER1 (FGT1) locus, with fgt1 mutants displaying reduced maintenance of heat-induced gene expression. FGT1 encodes the Arabidopsis thaliana orthologue of Strawberry notch (Sno), and the protein globally associates with the promoter regions of actively expressed genes in a heat-dependent fashion. FGT1 interacts with chromatin remodelers of the SWI/ SNF and ISWI families, which also display reduced heat stress memory. Genomic targets of the BRM remodeler overlap significantly with FGT1 targets. Accordingly, nucleosome dynamics at loci with altered maintenance of heat-induced expression are affected in fgt1. Together, our results suggest that by modulating nucleosome occupancy, FGT1 mediates stress-induced chromatin memory. Y1 - 2016 U6 - https://doi.org/10.7554/eLife.17061 SN - 2050-084X VL - 5 PB - eLife Sciences Publications CY - Cambridge ER -