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Publikation

Wijnker, E.; Harashima, H.; Müller, K.; Parra-Nuñez, P.; de Snoo, C. B.; van de Belt, J.; Rajjou, L.; Bayer, M.; Pradillo, M.; Schnittger, A.; The Cdk1/Cdk2 homolog CDKA;1 controls the recombination landscape in Arabidopsis Proc. Natl. Acad. Sci. U.S.A. 116, 12534-12539, (2019) DOI: 10.1073/pnas.1820753116

Little is known how patterns of cross-over (CO) numbers and distribution during meiosis are established. Here, we reveal that cyclin-dependent kinase A;1 (CDKA;1), the homolog of human Cdk1 and Cdk2, is a major regulator of meiotic recombination in Arabidopsis. Arabidopsis plants with reduced CDKA;1 activity experienced a decrease of class I COs, especially lowering recombination rates in centromere-proximal regions. Interestingly, this reduction of type I CO did not affect CO assurance, a mechanism by which each chromosome receives at least one CO, resulting in all chromosomes exhibiting similar genetic lengths in weak loss-of-function cdka;1 mutants. Conversely, an increase of CDKA;1 activity resulted in elevated recombination frequencies. Thus, modulation of CDKA;1 kinase activity affects the number and placement of COs along the chromosome axis in a dose-dependent manner.
Publikation

Harashima, H.; Dissmeyer, N.; Hammann, P.; Nomura, Y.; Kramer, K.; Nakagami, H.; Schnittger, A.; Modulation of plant growth in vivo and identification of kinase substrates using an analog-sensitive variant of CYCLIN-DEPENDENT KINASE A;1 BMC Plant Biol. 16, 209, (2016) DOI: 10.1186/s12870-016-0900-7

BackgroundModulation of protein activity by phosphorylation through kinases and subsequent de-phosphorylation by phosphatases is one of the most prominent cellular control mechanisms. Thus, identification of kinase substrates is pivotal for the understanding of many – if not all – molecular biological processes. Equally, the possibility to deliberately tune kinase activity is of great value to analyze the biological process controlled by a particular kinase.ResultsHere we have applied a chemical genetic approach and generated an analog-sensitive version of CDKA;1, the central cell-cycle regulator in Arabidopsis and homolog of the yeast Cdc2/CDC28 kinases. This variant could largely rescue a cdka;1 mutant and is biochemically active, albeit less than the wild type. Applying bulky kinase inhibitors allowed the reduction of kinase activity in an organismic context in vivo and the modulation of plant growth. To isolate CDK substrates, we have adopted a two-dimensional differential gel electrophoresis strategy, and searched for proteins that showed mobility changes in fluorescently labeled extracts from plants expressing the analog-sensitive version of CDKA;1 with and without adding a bulky ATP variant. A pilot set of five proteins involved in a range of different processes could be confirmed in independent kinase assays to be phosphorylated by CDKA;1 approving the applicability of the here-developed method to identify substrates.ConclusionThe here presented generation of an analog-sensitive CDKA;1 version is functional and represent a novel tool to modulate kinase activity in vivo and identify kinase substrates. Our here performed pilot screen led to the identification of CDK targets that link cell proliferation control to sugar metabolism, proline proteolysis, and glucosinolate production providing a hint how cell proliferation and growth are integrated with plant development and physiology.
Publikation

Faden, F.; Ramezani, T.; Mielke, S.; Almudi, I.; Nairz, K.; Froehlich, M. S.; Höckendorff, J.; Brandt, W.; Hoehenwarter, W.; Dohmen, R. J.; Schnittger, A.; Dissmeyer, N.; Phenotypes on demand via switchable target protein degradation in multicellular organisms Nat. Commun. 7, 12202, (2016) DOI: 10.1038/ncomms12202

Phenotypes on-demand generated by controlling activation and accumulation of proteins of interest are invaluable tools to analyse and engineer biological processes. While temperature-sensitive alleles are frequently used as conditional mutants in microorganisms, they are usually difficult to identify in multicellular species. Here we present a versatile and transferable, genetically stable system based on a low-temperature-controlled N-terminal degradation signal (lt-degron) that allows reversible and switch-like tuning of protein levels under physiological conditions in vivo. Thereby, developmental effects can be triggered and phenotypes on demand generated. The lt-degron was established to produce conditional and cell-type-specific phenotypes and is generally applicable in a wide range of organisms, from eukaryotic microorganisms to plants and poikilothermic animals. We have successfully applied this system to control the abundance and function of transcription factors and different enzymes by tunable protein accumulation.
Publikation

Harashima, H.; Dissmeyer, N.; Schnittger, A.; Cell cycle control across the eukaryotic kingdom Trends Cell Biol. 23, 345-356, (2013) DOI: 10.1016/j.tcb.2013.03.002

Almost two billion years of evolution have generated a vast and amazing variety of eukaryotic life with approximately 8.7 million extant species. Growth and reproduction of all of these organisms depend on faithful duplication and distribution of their chromosomes to the newly forming daughter cells in a process called the cell cycle. However, most of what is known today about cell cycle control comes from a few model species that belong to the unikonts; that is, to only one of five ‘supergroups’ that comprise the eukaryotic kingdom. Recently, analyzing species from distantly related clades is providing insights into general principles of cell cycle regulation and shedding light on its evolution. Here, referring to animal and fungal as opposed to non-unikont systems, especially flowering plants from the archaeplastid supergroup, we compare the conservation of central cell cycle regulator functions, the structure of network topologies, and the evolutionary dynamics of substrates of core cell cycle kinases.
Publikation

Zhao, X.; Harashima, H.; Dissmeyer, N.; Pusch, S.; Weimer, A. K.; Bramsiepe, J.; Bouyer, D.; Rademacher, S.; Nowack, M. K.; Novak, B.; Sprunck, S.; Schnittger, A.; A General G1/S-Phase Cell-Cycle Control Module in the Flowering Plant Arabidopsis thaliana PLOS Genet. 8, e1002847, (2012) DOI: 10.1371/journal.pgen.1002847

The decision to replicate its DNA is of crucial importance for every cell and, in many organisms, is decisive for the progression through the entire cell cycle. A comparison of animals versus yeast has shown that, although most of the involved cell-cycle regulators are divergent in both clades, they fulfill a similar role and the overall network topology of G1/S regulation is highly conserved. Using germline development as a model system, we identified a regulatory cascade controlling entry into S phase in the flowering plant Arabidopsis thaliana, which, as a member of the Plantae supergroup, is phylogenetically only distantly related to Opisthokonts such as yeast and animals. This module comprises the Arabidopsis homologs of the animal transcription factor E2F, the plant homolog of the animal transcriptional repressor Retinoblastoma (Rb)-related 1 (RBR1), the plant-specific F-box protein F-BOX-LIKE 17 (FBL17), the plant specific cyclin-dependent kinase (CDK) inhibitors KRPs, as well as CDKA;1, the plant homolog of the yeast and animal Cdc2+/Cdk1 kinases. Our data show that the principle of a double negative wiring of Rb proteins is highly conserved, likely representing a universal mechanism in eukaryotic cell-cycle control. However, this negative feedback of Rb proteins is differently implemented in plants as it is brought about through a quadruple negative regulation centered around the F-box protein FBL17 that mediates the degradation of CDK inhibitors but is itself directly repressed by Rb. Biomathematical simulations and subsequent experimental confirmation of computational predictions revealed that this regulatory circuit can give rise to hysteresis highlighting the here identified dosage sensitivity of CDK inhibitors in this network.
Publikation

Weimer, A. K.; Nowack, M. K.; Bouyer, D.; Zhao, X.; Harashima, H.; Naseer, S.; De Winter, F.; Dissmeyer, N.; Geldner, N.; Schnittger, A.; RETINOBLASTOMA RELATED1 Regulates Asymmetric Cell Divisions in Arabidopsis Plant Cell 24, 4083-4095, (2012) DOI: 10.1105/tpc.112.104620

Formative, also called asymmetric, cell divisions produce daughter cells with different identities. Like other divisions, formative divisions rely first of all on the cell cycle machinery with centrally acting cyclin-dependent kinases (CDKs) and their cyclin partners to control progression through the cell cycle. However, it is still largely obscure how developmental cues are translated at the cellular level to promote asymmetric divisions. Here, we show that formative divisions in the shoot and root of the flowering plant Arabidopsisthaliana are controlled by a common mechanism that relies on the activity level of the Cdk1 homolog CDKA;1, with medium levels being sufficient for symmetric divisions but high levels being required for formative divisions. We reveal that the function of CDKA;1 in asymmetric cell divisions operates through a transcriptional regulation system that is mediated by the Arabidopsis Retinoblastoma homolog RBR1. RBR1 regulates not only cell cycle genes, but also, independent of the cell cycle transcription factor E2F, genes required for formative divisions and cell fate acquisition, thus directly linking cell proliferation with differentiation. This mechanism allows the implementation of spatial information, in the form of high kinase activity, with intracellular gating of developmental decisions.
Publikation

Nowack, M.; Harashima, H.; Dissmeyer, N.; Zhao, X.; Bouyer, D.; Weimer, A.; De Winter, F.; Yang, F.; Schnittger, A.; Genetic Framework of Cyclin-Dependent Kinase Function in Arabidopsis Dev. Cell 22, 1030-1040, (2012) DOI: 10.1016/j.devcel.2012.02.015

Cyclin-dependent kinases (CDKs) are at the heart of eukaryotic cell-cycle control. The yeast Cdc2/CDC28 PSTAIRE kinase and its orthologs such as the mammalian Cdk1 have been found to be indispensable for cell-cycle progression in all eukaryotes investigated so far. CDKA;1 is the only PSTAIRE kinase in the flowering plant Arabidopsis and can rescue Cdc2/CDC28 mutants. Here, we show that cdka;1 null mutants are viable but display specific cell-cycle and developmental defects, e.g., in S phase entry and stem cell maintenance. We unravel that the crucial function of CDKA;1 is the control of the plant Retinoblastoma homolog RBR1 and that codepletion of RBR1 and CDKA;1 rescued most defects of cdka;1 mutants. Our work further revealed a basic cell-cycle control system relying on two plant-specific B1-type CDKs, and the triple cdk mutants displayed an early germline arrest. Taken together, our data indicate divergent functional differentiation of Cdc2-type kinases during eukaryote evolution.
Bücher und Buchkapitel

Pusch, S.; Dissmeyer, N.; Schnittger, A.; Bimolecular-Fluorescence Complementation Assay to Monitor Kinase–Substrate Interactions In Vivo (Dissmeyer, N. & Schnittger, A., eds.). Methods Mol. Biol. 779, 245-257, (2011) ISBN: 978-1-61779-264-9 DOI: 10.1007/978-1-61779-264-9_14

Enzyme–substrate interactions are weak and occur only transiently and thus, a faithful analysis of these interactions typically requires elaborated biochemical methodology. The bimolecular-fluorescence complementation (BiFC) assay, also referred to as split YFP assay, is a powerful and straightforward tool to test protein–protein interactions. This system is commonly used due to many advantages and especially due to its simple ease of use. BIFC relies on the reconstitution of an N-terminal and C-terminal half of YFP into a functional, i.e., fluorescent protein. Noteworthy, the dissociation constant of the two YFP halves is much lower than the association constant leading to a stabilization of the protein–protein interaction to be monitored. Whereas this property is sometimes critical, it also increases the sensitivity of the detection system by stabilizing transient interactions. Here, we exploit this property to detect and monitor interaction between a kinase and its substrate. In particular, we characterize with the BiFC system kinase-variants that show an altered substrate binding.
Bücher und Buchkapitel

Dissmeyer, N.; Schnittger, A.; Use of Phospho-Site Substitutions to Analyze the Biological Relevance of Phosphorylation Events in Regulatory Networks (Dissmeyer, N. & Schnittger, A., eds.). Methods Mol. Biol. 779, 93-138, (2011) ISBN: 978-1-61779-264-9 DOI: 10.1007/978-1-61779-264-9_6

Biological information is often transmitted by phosphorylation cascades. However, the biological relevance of specific phosphorylation events is often difficult to determine. An invaluable tool to study the effect of kinases and/or phosphatases is the use of phospho- and dephospho-mimetic substitutions in the respective target proteins. Here, we present a generally applicable procedure of how to design, set-up, and carry out phosphorylation modulation experiments and subsequent monitoring of protein activities, taking ­cyclin-dependent kinases (CDKs) as a case study. CDKs are key regulators of cell cycle progression in all eukaryotic cells. Consequently, CDKs are controlled at many levels and phosphorylation of CDKs ­themselves is used to regulate their kinase activity. We describe in detail complementation experiments of a mutant in CDKA;1, the major cell cycle kinase in Arabidopsis, with phosphorylation-site variants of CDKA;1. CDKA;1 versions were generated either by mimicking a phosphorylated amino acid by replacing the respective residue with a negatively charged amino acid, e.g., aspartate or glutamate, or by mutating it to a non-phoshorylatable amino acid, such as alanine, valine, or phenylalanine. The genetic complementation studies were accompanied by the isolation of these kinase variants from plant extract and subsequent kinase assays to determine changes in their activity levels. This work allowed us to judge the importance of ­posttranslational regulation of CDKA;1 in plants and has shown that the molecular mechanistics of CDK function are apparently conserved across the kingdoms. However, the regulatory wiring of CDKs is ­strikingly different between plants, animals, and yeast.
Bücher und Buchkapitel

Dissmeyer, N.; Schnittger, A.; The Age of Protein Kinases (Dissmeyer, N. & Schnittger, A., eds.). Methods Mol. Biol. 779, 7-52, (2011) ISBN: 978-1-61779-264-9 DOI: 10.1007/978-1-61779-264-9_2

Major progress has been made in unravelling of regulatory mechanisms in eukaryotic cells. Modification of target protein properties by reversible phosphorylation events has been found to be one of the most prominent cellular control processes in all organisms. The phospho-status of a protein is dynamically controlled by protein kinases and counteracting phosphatases. Therefore, monitoring of kinase and phosphatase activities, identification of specific phosphorylation sites, and assessment of their functional significance are of crucial importance to understand development and homeostasis. Recent advances in the area of molecular biology and biochemistry, for instance, mass spectrometry-based phosphoproteomics or fluorescence spectroscopical methods, open new possibilities to reach an unprecidented depth and a proteome-wide understanding of phosphorylation processes in plants and other species. In addition, the growing number of model species allows now deepening evolutionary insights into signal transduction cascades and the use of kinase/phosphatase systems. Thus, this is the age where we move from an understanding of the structure and function of individual protein modules to insights how these proteins are organized into pathways and networks. In this introductory chapter, we briefly review general definitions, methodology, and current concepts of the molecular mechanisms of protein kinase function as a foundation for this methods book. We briefly review biochemistry and structural biology of kinases and provide selected examples for the role of kinases in biological systems.
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