Doctor of Philosophy, Universitat Wien (2016)
Magister, Universitat Wien (2009)
Dominique Bergmann, Postdoctoral Faculty Sponsor
Snf1-RELATED KINASE1-Controlled C/S1-bZIP Signaling Activates Alternative Mitochondrial Metabolic Pathways to Ensure Plant Survival in Extended Darkness.
The Plant cell
2018; 30 (2): 495–509
Sustaining energy homeostasis is of pivotal importance for all living organisms. InArabidopsis thaliana, evolutionarily conserved SnRK1 kinases (Snf1-RELATED KINASE1) control metabolic adaptation during low energy stress. To unravel starvation-induced transcriptional mechanisms, we performed transcriptome studies of inducible knockdown lines and found that S1-basic leucine zipper transcription factors (S1-bZIPs) control a defined subset of genes downstream of SnRK1. For example, S1-bZIPs coordinate the expression of genes involved in branched-chain amino acid catabolism, which constitutes an alternative mitochondrial respiratory pathway that is crucial for plant survival during starvation. Molecular analyses defined S1-bZIPs as SnRK1-dependent regulators that directly control transcription via binding to G-box promoter elements. Moreover, SnRK1 triggers phosphorylation of group C-bZIPs and the formation of C/S1-heterodimers and, thus, the recruitment of SnRK1 directly to target promoters. Subsequently, the C/S1-bZIP-SnRK1 complex interacts with the histone acetylation machinery to remodel chromatin and facilitate transcription. Taken together, this work reveals molecular mechanisms underlying how energy deprivation is transduced to reprogram gene expression, leading to metabolic adaptation upon stress.
View details for DOI 10.1105/tpc.17.00414
View details for PubMedID 29348240
Redox state-dependent modulation of plant SnRK1 kinase activity differs from AMPK regulation in animals.
The evolutionarily highly conserved SNF1-related protein kinase (SnRK1) protein kinase is a metabolic master regulator in plants, balancing the critical energy consumption between growth- and stress response-related metabolic pathways. While the regulation of the mammalian [AMP-activated protein kinase (AMPK)] and yeast (SNF1) orthologues of SnRK1 is well-characterised, the regulation of SnRK1 kinase activity in plants is still an open question. Here we report that the activity and T-loop phosphorylation of AKIN10, the kinase subunit of the SnRK1 complex, is regulated by the redox status. Although this regulation is dependent on a conserved cysteine residue, the underlying mechanism is different to the redox regulation of animal AMPK and has functional implications for the regulation of the kinase complex in plants under stress conditions.
View details for DOI 10.1002/1873-3468.12852
View details for PubMedID 28940407
Know where your clients are: subcellular localization and targets of calcium-dependent protein kinases
JOURNAL OF EXPERIMENTAL BOTANY
2016; 67 (13): 3855-3872
Calcium-dependent protein kinases (CDPKs) are at the forefront of decoding transient Ca(2+) signals into physiological responses. They play a pivotal role in many aspects of plant life starting from pollen tube growth, during plant development, and in stress response to senescence and cell death. At the cellular level, Ca(2+) signals have a distinct, narrow distribution, thus requiring a conjoined localization of the decoders. Accordingly, most CDPKs have a distinct subcellular distribution which enables them to 'sense' the local Ca(2+) concentration and to interact specifically with their targets. Here we present a comprehensive overview of identified CDPK targets and discuss them in the context of kinase-substrate specificity and subcellular distribution of the CDPKs. This is particularly relevant for calcium-mediated phosphorylation where different CDPKs, as well as other kinases, were frequently reported to be involved in the regulation of the same target. However, often these studies were not performed in an in situ context. Thus, considering the specific expression patterns, distinct subcellular distribution, and different Ca(2+) affinities of CDPKs will narrow down the number of potential CDPKs for one given target. A number of aspects still remain unresolved, giving rise to pending questions for future research.
View details for DOI 10.1093/jxb/erw157
View details for Web of Science ID 000382058600006
View details for PubMedID 27117335
Quantitative phosphoproteomics reveals the role of the AMPK plant ortholog SnRK1 as a metabolic master regulator under energy deprivation.
2016; 6: 31697-?
Since years, research on SnRK1, the major cellular energy sensor in plants, has tried to define its role in energy signalling. However, these attempts were notoriously hampered by the lethality of a complete knockout of SnRK1. Therefore, we generated an inducible amiRNA::SnRK1α2 in a snrk1α1 knock out background (snrk1α1/α2) to abolish SnRK1 activity to understand major systemic functions of SnRK1 signalling under energy deprivation triggered by extended night treatment. We analysed the in vivo phosphoproteome, proteome and metabolome and found that activation of SnRK1 is essential for repression of high energy demanding cell processes such as protein synthesis. The most abundant effect was the constitutively high phosphorylation of ribosomal protein S6 (RPS6) in the snrk1α1/α2 mutant. RPS6 is a major target of TOR signalling and its phosphorylation correlates with translation. Further evidence for an antagonistic SnRK1 and TOR crosstalk comparable to the animal system was demonstrated by the in vivo interaction of SnRK1α1 and RAPTOR1B in the cytosol and by phosphorylation of RAPTOR1B by SnRK1α1 in kinase assays. Moreover, changed levels of phosphorylation states of several chloroplastic proteins in the snrk1α1/α2 mutant indicated an unexpected link to regulation of photosynthesis, the main energy source in plants.
View details for DOI 10.1038/srep31697
View details for PubMedID 27545962
SnRK1-triggered switch of bZIP63 dimerization mediates the low-energy response in plants
Metabolic adjustment to changing environmental conditions, particularly balancing of growth and defense responses, is crucial for all organisms to survive. The evolutionary conserved AMPK/Snf1/SnRK1 kinases are well-known metabolic master regulators in the low-energy response in animals, yeast and plants. They act at two different levels: by modulating the activity of key metabolic enzymes, and by massive transcriptional reprogramming. While the first part is well established, the latter function is only partially understood in animals and not at all in plants. Here we identified the Arabidopsis transcription factor bZIP63 as key regulator of the starvation response and direct target of the SnRK1 kinase. Phosphorylation of bZIP63 by SnRK1 changed its dimerization preference, thereby affecting target gene expression and ultimately primary metabolism. A bzip63 knock-out mutant exhibited starvation-related phenotypes, which could be functionally complemented by wild type bZIP63, but not by a version harboring point mutations in the identified SnRK1 target sites.
View details for DOI 10.7554/eLife.05828
View details for Web of Science ID 000373809400001
View details for PubMedID 26263501
Solving the Differential Biochemical Jacobian from Metabolomics Covariance Data
2014; 9 (4)
High-throughput molecular analysis has become an integral part in organismal systems biology. In contrast, due to a missing systematic linkage of the data with functional and predictive theoretical models of the underlying metabolic network the understanding of the resulting complex data sets is lacking far behind. Here, we present a biomathematical method addressing this problem by using metabolomics data for the inverse calculation of a biochemical Jacobian matrix, thereby linking computer-based genome-scale metabolic reconstruction and in vivo metabolic dynamics. The incongruity of metabolome coverage by typical metabolite profiling approaches and genome-scale metabolic reconstruction was solved by the design of superpathways to define a metabolic interaction matrix. A differential biochemical Jacobian was calculated using an approach which links this metabolic interaction matrix and the covariance of metabolomics data satisfying a Lyapunov equation. The predictions of the differential Jacobian from real metabolomic data were found to be correct by testing the corresponding enzymatic activities. Moreover it is demonstrated that the predictions of the biochemical Jacobian matrix allow for the design of parameter optimization strategies for ODE-based kinetic models of the system. The presented concept combines dynamic modelling strategies with large-scale steady state profiling approaches without the explicit knowledge of individual kinetic parameters. In summary, the presented strategy allows for the identification of regulatory key processes in the biochemical network directly from metabolomics data and is a fundamental achievement for the functional interpretation of metabolomics data.
View details for DOI 10.1371/journal.pone.0092299
View details for Web of Science ID 000334103000018
View details for PubMedID 24695071
Metabolism and development - integration of micro computed tomography data and metabolite profiling reveals metabolic reprogramming from floral initiation to silique development
2014; 202 (1): 322-335
The interrelationship of morphogenesis and metabolism is a poorly studied phenomenon. The main paradigm is that development is controlled by gene expression. The aim of the present study was to correlate metabolism to early and late stages of flower and fruit development in order to provide the basis for the identification of metabolic adjustment and limitations. A highly detailed picture of morphogenesis is achieved using nondestructive micro computed tomography. This technique was used to quantify morphometric parameters of early and late flower development in an Arabidopsis thaliana mutant with synchronized flower initiation. The synchronized flower phenotype made it possible to sample enough early floral tissue otherwise not accessible for metabolomic analysis. The integration of metabolomic and morphometric data enabled the correlation of metabolic signatures with the process of flower morphogenesis. These signatures changed significantly during development, indicating a pronounced metabolic reprogramming in the tissue. Distinct sets of metabolites involved in these processes were identified and were linked to the findings of previous gene expression studies of flower development. High correlations with basic leucine zipper (bZIP) transcription factors and nitrogen metabolism genes involved in the control of metabolic carbon : nitrogen partitioning were revealed. Based on these observations a model for metabolic adjustment during flower development is proposed.
View details for DOI 10.1111/nph.12631
View details for Web of Science ID 000331737900038
View details for PubMedID 24350948
Phosphorylation of Arabidopsis transketolase at Ser(428) provides a potential paradigm for the metabolic control of chloroplast carbon metabolism
2014; 458: 313-322
Calcium is an important second messenger in eukaryotic cells that regulates many different cellular processes. To elucidate calcium regulation in chloroplasts, we identified the targets of calcium-dependent phosphorylation within the stromal proteome. A 73 kDa protein was identified as one of the most dominant proteins undergoing phosphorylation in a calcium-dependent manner in the stromal extracts of both Arabidopsis and Pisum. It was identified as TKL (transketolase), an essential enzyme of both the Calvin-Benson-Bassham cycle and the oxidative pentose phosphate pathway. Calcium-dependent phosphorylation of both Arabidopsis isoforms (AtTKL1 and AtTKL2) could be confirmed in vitro using recombinant proteins. The phosphorylation is catalysed by a stroma-localized protein kinase, which cannot utilize GTP. Phosphorylation of AtTKL1, the dominant isoform in most tissues, occurs at a serine residue that is conserved in TKLs of vascular plants. By contrast, an aspartate residue is present in this position in cyanobacteria, algae and mosses. Characterization of a phosphomimetic mutant (S428D) indicated that Ser428 phosphorylation exerts significant effects on the enzyme's substrate saturation kinetics at specific physiological pH values. The results of the present study point to a role for TKL phosphorylation in the regulation of carbon allocation.
View details for DOI 10.1042/BJ20130631
View details for Web of Science ID 000333718300013
View details for PubMedID 24328790
- Shaping the pathogen response by protein kinase triggered oxidative burst NEW PHYTOLOGIST 2012; 196 (1): 4-6
Plant organellar calcium signalling: an emerging field
JOURNAL OF EXPERIMENTAL BOTANY
2012; 63 (4): 1525-1542
This review provides a comprehensive overview of the established and emerging roles that organelles play in calcium signalling. The function of calcium as a secondary messenger in signal transduction networks is well documented in all eukaryotic organisms, but so far existing reviews have hardly addressed the role of organelles in calcium signalling, except for the nucleus. Therefore, a brief overview on the main calcium stores in plants-the vacuole, the endoplasmic reticulum, and the apoplast-is provided and knowledge on the regulation of calcium concentrations in different cellular compartments is summarized. The main focus of the review will be the calcium handling properties of chloroplasts, mitochondria, and peroxisomes. Recently, it became clear that these organelles not only undergo calcium regulation themselves, but are able to influence the Ca(2+) signalling pathways of the cytoplasm and the entire cell. Furthermore, the relevance of recent discoveries in the animal field for the regulation of organellar calcium signals will be discussed and conclusions will be drawn regarding potential homologous mechanisms in plant cells. Finally, a short overview on bacterial calcium signalling is included to provide some ideas on the question where this typically eukaryotic signalling mechanism could have originated from during evolution.
View details for DOI 10.1093/jxb/err394
View details for Web of Science ID 000301005200002
View details for PubMedID 22200666
Chloroplast-localized protein kinases: a step forward towards a complete inventory
JOURNAL OF EXPERIMENTAL BOTANY
2012; 63 (4): 1713-1723
In addition to redox regulation, protein phosphorylation has gained increasing importance as a regulatory principle in chloroplasts in recent years. However, only very few chloroplast-localized protein kinases have been identified to date. Protein phosphorylation regulates important chloroplast processes such as photosynthesis or transcription. In order to better understand chloroplast function, it is therefore crucial to obtain a complete picture of the chloroplast kinome, which is currently constrained by two effects: first, recent observations showed that the bioinformatics-based prediction of chloroplast-localized protein kinases from available sequence data is strongly biased; and, secondly, protein kinases are of very low abundance, which makes their identification by proteomics approaches extremely difficult. Therefore, the aim of this study was to obtain a complete list of chloroplast-localized protein kinases from different species. Evaluation of protein kinases which were either highly predicted to be chloroplast localized or have been identified in different chloroplast proteomic studies resulted in the confirmation of only three new kinases. Considering also all reports of experimentally verified chloroplast protein kinases to date, compelling evidence was found for a total set of 15 chloroplast-localized protein kinases in different species. This is in contrast to a much higher number that would be expected based on targeting prediction or on the general abundance of protein kinases in relation to the entire proteome. Moreover, it is shown that unusual protein kinases with differing ATP-binding sites or catalytic centres seem to occur frequently within the chloroplast kinome, thus making their identification by mass spectrometry-based approaches even more difficult due to a different annotation.
View details for DOI 10.1093/jxb/err377
View details for Web of Science ID 000301005200014
View details for PubMedID 22282538
Cross-talk of calcium-dependent protein kinase and MAP kinase signaling.
Plant signaling & behavior
2011; 6 (1): 8-12
Plants use different signalling pathways to acclimate to changing environmental conditions. Fast changes in the concentration of free Ca(2+) ions - so called Ca(2+) signals - are among the first responses to many stress situations. These signals are decoded by different types of calcium-dependent protein kinases, which - together with mitogen-activated protein kinases (MAPK) - present two major pathways that are widely used to adapt the cellular metabolism to a changing environment. Ca(2+)-dependent protein kinase (CDPK) and MAPK pathways are known to be involved in signalling of abiotic and biotic stress in animal, yeast and plant cells. In many cases both pathways are activated in response to the same stimuli leading to the question of a potential cross-talk between those pathways. Cross-talk between Ca(2+)-dependent and MAPK signalling pathways has been elaborately studied in animal cells, but it has hardly been investigated in plants. Early studies of CDPKs involved in the biotic stress response in tobacco indicated a cross-talk of CDPK and MAPK activities, whereas a recent study in Arabidopsis revealed that CDPKs and MAPKs act differentially in innate immune signalling and showed no direct cross-talk between CDPK and MAPK activities. Similar results were also reported for CDPK and MAPK activities in the salt stress response in Arabidopsis. Different modes of action are furthermore supported by the different subcellular localization of the involved kinases. In this review, we discuss recent findings on CDPK and MAPK signalling with respect to potential cross-talk and the subcellular localization of the involved components.
View details for PubMedID 21248475