TY - THES A1 - Müller-Röber, Bernd T1 - Molekularphysiologische Ansätze zur Analyse primärer Stoffwechselwege und stomatärer Funktionsprozesse in Höheren Pflanzen : Darstellung der publizierten Forschungsergebnisse unter Berücksichtigung des allgemeinen Kenntnisstands und Einordnung in den wissenschaftlichen Gesamtzusammenhang Y1 - 1997 ER - TY - JOUR A1 - Gomez-Merino, Fernando Carlos A1 - Brearley, C. A. A1 - Ornatowska, Magdalena A1 - Abdel-Haliem, Mahmoud E. F. A1 - Zanor, Maria Ines A1 - Müller-Röber, Bernd T1 - AtDGK2, a novel diacylglycerol kinase from Arabidopsis thaliana, phosphorylates 1-stearoyl-2-arachidonoyl-sn- glycerol and 1,2-dioleoyl-sn-glycerol and exhibits cold-inducible gene expression N2 - Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DAG) to generate phosphatidic acid (PA). Both DAG and PA are implicated in signal transduction pathways. DGKs have been widely studied in animals, but their analysis in plants is fragmentary. Here, we report the cloning and biochemical characterization of AtDGK2, encoding DGK from Arabidopsis thaliana. AtDGK2 has a predicted molecular mass of 79.4 kDa and, like AtDGK1 previously reported, harbors two copies of a phorbol ester/DAG-binding domain in its N-terminal region. AtDGK2 belongs to a family of seven DGK genes in A. thaliana. AtDGK3 to AtDGK7 encode similar to55-kDa DGKs that lack a typical phorbol ester/DAG-binding domain. Phylogenetically, plant DGKs fall into three clusters. Members of all three clusters are widely expressed in vascular plants. Recombinant AtDGK2 was expressed in Escherichia coli and biochemically characterized. The enzyme phosphorylated 1,2-dioleoyl-sn-glycerol to yield PA, exhibiting Michaelis-Menten type kinetics. Estimated K-m and V-max values were 125 muM for DAG and 0.25 pmol of PA min(-1) mug(-1), respectively. The enzyme was maximally active at pH 7.2. Its activity was Mg2+-dependent and affected by the presence of detergents, salts, and the DGK inhibitor R59022, but not by Ca2+. AtDGK2 exhibited substrate preference for unsaturated DAG analogues (i.e. 1-stearoyl-2-arachidonoyl-sn-glycerol and 1,2- dioleoyl-sn-glycerol). The AtDGK2 gene is expressed in various tissues of the Arabidopsis plant, including leaves, roots, and flowers, as shown by Northern blot analysis and promoter-reporter gene fusions. We found that AtDGK2 is induced by exposure to low temperature (4degreesC), pointing to a role in cold signal transduction Y1 - 2004 SN - 0021-9258 ER - TY - JOUR A1 - Dreyer, Ingo A1 - Poree, Fabien A1 - Schneider, A. A1 - Mittelstadt, J. A1 - Bertl, Adam A1 - Sentenac, H. A1 - Thibaud, Jean-Baptiste A1 - Müller-Röber, Bernd T1 - Assembly of plant Shaker-like K-out channels requires two distinct sites of the channel alpha-subunit N2 - SKOR and GORK are outward-rectifying plant potassium channels from Arabidopsis thaliana. They belong to the Shaker superfamily of voltage-dependent K+ channels. Channels of this class are composed of four alpha-subunits and subunit assembly is a prerequisite for channel function. In this study the assembly mechanism of SKOR was investigated using the yeast two-hybrid system and functional assays in Xenopus oocytes and in yeast. We demonstrate that SKOR and GORK physically interact and assemble into heteromeric K-out channels. Deletion mutants and chimeric proteins generated from SKOR and the K-in channel alpha-subunit KAT1 revealed that the cytoplasmic C-terminus of SKOR determines channel assembly. Two domains thatchannel a-subunit KAT1 revealed that the cytoplasmic C-terminus of SKOR determines channel assembly. Two domains that are crucial for channel assembly were identified: i), a proximal interacting region comprising a putative cyclic nucleotide-binding domain together with 33 amino acids just upstream of this domain, and ii), a distal interacting region showing some resemblance to the K-T domain of KAT1. Both regions contributed differently to channel assembly. Whereas the proximal interacting region was found to be active on its own, the distal interacting region required an intact proximal interacting region to be active. K-out alpha-subunits did not assemble with K-in alpha-subunits because of the absence of interaction between their assembly sites Y1 - 2004 SN - 0006-3495 ER - TY - JOUR A1 - Witt, Isabell A1 - Zanor, Maria Ines A1 - Müller-Röber, Bernd T1 - Transcription factor function search : how do individual factors regulate agronomical important processes in plants? (Subproject A) Y1 - 2004 SN - 3-00-011587-0 ER - TY - JOUR A1 - Kohler, B. A1 - Müller-Röber, Bernd T1 - Remote control - cell and organ communication within plants Y1 - 2004 ER - TY - JOUR A1 - Becker, Dirk A1 - Geiger, D. A1 - Dunkel, M. A1 - Roller, A. A1 - Bertl, Adam A1 - Latz, A. A1 - Carpaneto, Armando A1 - Dietrich, Peter A1 - Roelfsema, M. R. G. A1 - Voelker, C. A1 - Schmidt, D. A1 - Müller-Röber, Bernd A1 - Czempinski, Katrin A1 - Hedrich, R. T1 - AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+- dependent manner N2 - The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium Y1 - 2004 SN - 0027-8424 ER - TY - JOUR A1 - Gomez-Merino, Fernando Carlos A1 - Arana-Ceballos, Fernando Alberto A1 - Trejo-Tellez, L. I. A1 - Skirycz, Aleksandra A1 - Brearley, C. A. A1 - Dormann, P. A1 - Müller-Röber, Bernd T1 - Arabidopsis AtDGK7, the smallest member of plant diacylglycerol kinases (DGKs), displays unique biochemical features and saturates at low substrate concentration : the DGK inhibitor R59022 differentially affects AtDGK2 and AtDGK7 activity in vitro and alters plant growth and development N2 - Diacylglycerol kinase (DGK) regulates the level of the second messenger diacylglycerol and produces phosphatidic acid (PA), another signaling molecule. The Arabidopsis thaliana genome encodes seven putative diacylglycerol kinase isozymes (named AtDGK1 to -7), structurally falling into three major clusters. So far, enzymatic activity has not been reported for any plant Cluster II DGK. Here, we demonstrate that a representative of this cluster, AtDGK7, is biochemically active when expressed as a recombinant protein in Escherichia coli. AtDGK7, encoded by gene locus At4g30340, contains 374 amino acids with an apparent molecular mass of 41.2 kDa. AtDGK7 harbors an N-terminal catalytic domain, but in contrast to various characterized DGKs (including AtDGK2), it lacks a cysteine-rich domain at its N terminus, and, importantly, its C-terminal DGK accessory domain is incomplete. Recombinant AtDGK7 expressed in E. coli exhibits Michaelis-Menten type kinetics with 1,2-dioleoyl-sn-glycerol as substrate. AtDGK7 activity was affected by pH, detergents, and the DGK inhibitor R59022. We demonstrate that both AtDGK2 and AtDGK7 phosphorylate diacylglycerol molecular species that are typically found in plants, indicating that both enzymes convert physiologically relevant substrates. AtDGK7 is expressed throughout the Arabidopsis plant, but expression is strongest in flowers and young seedlings. Expression of AtDGK2 is transiently induced by wounding. R59022 at similar to 80 mu M inhibits root elongation and lateral root formation and reduces plant growth, indicating that DGKs play an important role in plant development Y1 - 2005 SN - 0021-9258 ER - TY - JOUR A1 - Michard, Erwan A1 - Lacombe, Benoît A1 - Poree, Fabien A1 - Müller-Röber, Bernd A1 - Sentenac, Hervé A1 - Thibaud, Jean-Baptiste A1 - Dreyer, Ingo T1 - A unique voltage sensor sensitizes the potassium channel AKT2 to phosphoregulation N2 - Among all voltage-gated K+ channels from the model plant Arabidopsis thaliana, the weakly rectifying K+ channel (K-weak channel) AKT2 displays unique gating properties. AKT2 is exceptionally regulated by phosphorylation: when nonphosphorylated AKT2 behaves as an inward-rectifying potassium channel; phosphorylation of AKT2 abolishes inward rectification by shifting its activation threshold far positive (>200 mV) so that it closes only at voltages positive of + 100 mV. In its phosphorylated form, AKT2 is thus locked in the open state in the entire physiological voltage range. To understand the molecular grounds of this unique gating behavior, we generated chimeras between AKT2 and the conventional inward-rectifying channel KAT1. The transfer of the pore from KAT1 to AKT2 altered the permeation properties of the channel. However, the gating properties were unaffected, suggesting that the pore region of AKT2 is not responsible for the unique K-weak gating. Instead, a lysine residue in S4, highly conserved among all K-weak channels but absent from other plant K+ channels, was pinpointed in a site-directed mutagenesis approach. Substitution of the lysine by serine or aspartate abolished the "open-lock" characteristic and converted AKT2 into an inward- rectifying channel. Interestingly, phosphoregulation of the mutant AKT2-K197S appeared to be similar to that of the K-in channel KAT1: as suggested by mimicking the phosphorylated and dephosphorylated states, phosphorylation induced a shift of the activation threshold of AKT2-K197S by about +50 mV. We conclude that the lysine residue K197 sensitizes AKT2 to phosphoregulation. The phosphorylation-induced reduction of the activation energy in AKT2 is similar to 6 kT larger than in the K197S mutant. It is discussed that this hypersensitive response of AKT2 to phosphorylation equips a cell with the versatility to establish a potassium gradient and to make efficient use of it Y1 - 2005 ER - TY - JOUR A1 - Lin, W. H. A1 - Wang, Y. A1 - Müller-Röber, Bernd A1 - Brearley, C. A. A1 - Xu, Z. H. A1 - Xue, H. W. T1 - At5PTase13 modulates cotyledon vein development through regulating auxin homeostasis N2 - Phosphatidylinositol signaling pathway and the relevant metabolites are known to be critical to the modulation of different aspects of plant growth, development, and stress responses. Inositol polyphosphate 5-phosphatase is a key enzyme involved in phosphatidylinositol metabolism and is encoded by an At5PTase gene family in Arabidopsis thaliana. A previous study shows that At5PTase11 mediates cotyledon vascular development probably through the regulation of intracellular calcium levels. In this study, we provide evidence that At5PTase13 modulates the development of cotyledon veins through its regulation of auxin homeostasis. A T-DNA insertional knockout mutant, At5pt13-1, showed a defect in development of the cotyledon vein, which was rescued completely by exogenous auxin and in part by brassinolide, a steroid hormone. Furthermore, the mutant had reduced auxin content and altered auxin accumulation in seedlings revealed by the DR5:beta-glucuronidase fusion construct in seedlings. In addition, microarray analysis shows that the transcription of key genes responsible for auxin biosynthesis and transport was altered in At5pt13-1. The At5pt13-1 mutant was also less sensitive to auxin inhibition of root elongation. These results suggest that At5PTase13 regulates the homeostasis of auxin, a key hormone controlling vascular development in plants Y1 - 2005 SN - 0032-0889 ER - TY - JOUR A1 - Riano-Pachon, Diego Mauricio A1 - Dreyer, Ingo A1 - Müller-Röber, Bernd T1 - Orphan transcripts in Arabidopsis thaliana : identification of several hundred previously unrecognized genes N2 - Expressed sequence tags (ESTs) represent a huge resource for the discovery of previously unknown genetic information and functional genome assignment. In this study we screened a collection of 178 292 ESTs from Arabidopsis thaliana by testing them against previously annotated genes of the Arabidopsis genome. We identified several hundreds of new transcripts that match the Arabidopsis genome at so far unassigned loci. The transcriptional activity of these loci was independently confirmed by comparison with the Salk Whole Genome Array Data. To a large extent, the newly identified transcriptionally active genomic regions do not encode 'classic' proteins, but instead generate non-coding RNAs and/or small peptide-coding RNAs of presently unknown biological function. More than 560 transcripts identified in this study are not represented by the Affymetrix GeneChip arrays currently widely used for expression profiling in A. thaliana. Our data strongly support the hypothesis that numerous previously unknown genes exist in the Arabidopsis genome Y1 - 2005 SN - 0960-7412 ER - TY - JOUR A1 - Xu, J. A1 - Brearley, C. A. A1 - Lin, W. H. A1 - Wang, Y. A1 - Ye, R. A1 - Müller-Röber, Bernd A1 - Xu, Z. H. A1 - Xue, H. W. T1 - A role of Arabidopsis inositol polyphosphate kinase, AtIPK2 alpha, in pollen germination and root growth N2 - Inositol polyphosphates, such as inositol trisphosphate, are pivotal intracellular signaling molecules in eukaryotic cells. In higher plants the mechanism for the regulation of the type and the level of these signaling molecules is poorly understood. In this study we investigate the physiological function of an Arabidopsis (Arabidopsis thaliana) gene encoding inositol polyphosphate kinase (AtIPK2alpha), which phosphorylates inositol 1,4,5-trisphosphate successively at the D-6 and D-3 positions, and inositol 1,3,4,5-tetrakisphosphate at D-6, resulting in the generation of inositol 1,3,4,5,6-pentakisphosphate. Semiquantitative reverse transcription-PCR and promoter-beta-glucuronidase reporter gene analyses showed that AtIPK2alpha is expressed in various tissues, including roots and root hairs, stem, leaf, pollen grains, pollen tubes, the flower stigma, and siliques. Transgenic Arabidopsis plants expressing the AtIPK2alpha antisense gene under its own promoter were generated. Analysis of several independent transformants exhibiting strong reduction in AtIPK2alpha transcript levels showed that both pollen germination and pollen tube growth were enhanced in the antisense lines compared to wild-type plants, especially in the presence of nonoptimal low Ca2+ concentrations in the culture medium. Furthermore, root growth and root hair development were also stimulated in the antisense lines, in the presence of elevated external Ca2+ concentration or upon the addition of EGTA. In addition, seed germination and early seedling growth was stimulated in the antisense lines. These observations suggest a general and important role of AtIPK2alpha, and hence inositol polyphosphate metabolism, in the regulation of plant growth most likely through the regulation of calcium signaling, consistent with the well-known function of inositol trisphosphate in the mobilization of intracellular calcium stores Y1 - 2005 SN - 0032-0889 ER - TY - JOUR A1 - Johansson, Ingela A1 - Wulfetange, Klaas A1 - Poree, Fabien A1 - Michard, Erwan A1 - Gajdanowicz, Pawel A1 - Lacombe, Benoit A1 - Sentenac, Herve A1 - Thibaud, Jean-Baptiste A1 - Müller-Röber, Bernd A1 - Blatt, Michael R. A1 - Dreyer, Ingo T1 - External K+ modulates the activity of the Arabidopsis potassium channel SKOR via an unusual mechanism N2 - Plant outward-rectifying K+ channels mediate K+ efflux from guard cells during stomatal closure and from root cells into the xylem for root-shoot allocation of potassium (K). Intriguingly, the gating of these channels depends on the extracellular K+ concentration, although the ions carrying the current are derived from inside the cell. This K+ dependence confers a sensitivity to the extracellular K+ concentration ([K+]) that ensures that the channels mediate K+ efflux only, regardless of the [K+] prevailing outside. We investigated the mechanism of K+-dependent gating of the K+ channel SKOR of Arabidopsis by site-directed mutagenesis. Mutations affecting the intrinsic K+ dependence of gating were found to cluster in the pore and within the sixth transmembrane helix (S6), identifying an 'S6 gating domain' deep within the membrane. Mapping the SKOR sequence to the crystal structure of the voltage-dependent K+ channel KvAP from Aeropyrum pernix suggested interaction between the S6 gating domain and the base of the pore helix, a prediction supported by mutations at this site. These results offer a unique insight into the molecular basis for a physiologically important K+-sensory process in plants Y1 - 2006 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0960-7412 U6 - https://doi.org/10.1111/j.1365-313X.2006.02690.X SN - 0960-7412 ER - TY - JOUR A1 - Feng, Xiao-Li A1 - Ni, Wei-Min A1 - Elge, Stephan A1 - Müller-Röber, Bernd A1 - Xu, Zhi-Hong A1 - Xue, Hong-Wei T1 - Auxin flow in anther filaments is critical for pollen grain development through regulating pollen mitosis N2 - It was well known that auxin is critical for anther/pollen grain development, however, the clear distribution and detailed effects of auxin during floral development are still unclear. We have shown here that, through analyzing GUS activities of Arabidopsis lines harboring auxin response elements DR5-GUS, auxin was mainly accumulated in the anther during flower stages 10-12. Further studies employing the indoleacetic acid-lysine synthetase (iaaL) coding gene from Pseudomonas syringae subsp. savastanoi under control of the promoter region of Arabidopsis phosphatidylinositol monophosphate 5-kinase 1 gene, which conducts the anther filament-specific expression, showed that block of auxin flow of filaments resulted in shortened filaments and significantly defective pollen grains. Similar phenotype was observed in tobacco plants transformed with the same construct, confirming the effects of auxin flow in filaments on anther development. Detailed studies further revealed that the meiosis process of pollen grain was normal while the mitosis at later stage was significantly defected, indicating the effects of auxin flow in filaments on pollen grain mitosis process. Analysis employing [C-14]IAA, as well as the observation on the expression of AtPIN1, coding for auxin efflux carrier, demonstrated the presence of polar auxin transport in anther filaments and pollen grains Y1 - 2006 UR - http://www.springerlink.com/content/100330 U6 - https://doi.org/10.1007/s11103-006-0005-z SN - 0167-4412 ER - TY - GEN A1 - Lou, Ying A1 - Ma, Hui A1 - Lin, Wen-Hui A1 - Chu, Zhao-Quing A1 - Müller-Röber, Bernd A1 - Xu, Zhi-Hong A1 - Xue, Hong-Wei T1 - The highly charged region of plant beta-type phosphatidylinositol 4-kinase is involved in membrane targeting and phospholipid binding N2 - In Arabidopsis thaliana and Oryza sativa, two types of PI 4-kinase (PI4Ks) have been isolated and functionally characterized. The alpha-type PI4Ks (similar to 220 kDa) contain a PH domain, which is lacking in beta-type PI4Ks (similar to 120 kDa). beta-Type PI4Ks, exemplified by Arabidopsis AtPI4K beta and rice OsPI4K2, contain a highly charged repetitive segment designated PPC (Plant PI4K Charged) region, which is an unique domain only found in plant beta-type PI4Ks at present. The PPC region has a length of similar to 300 amino acids and harboring 11 (AtPI4K beta) and 14 (OsPI4K2) repeats, respectively, of a 20-aa motif. Studies employing a modified yeast-based "Sequence of Membrane- Targeting Detection'' system demonstrate that the PPC(OsPI4K2) region, as well as the former 8 and latter 6 repetitive motifs within the PPC region, are able to target fusion proteins to the plasma membrane. Further detection on the transiently expressed GFP fusion proteins in onion epidermal cells showed that the PPC(OsPI4K2) region alone, as well as the region containing repetitive motifs 1-8, was able to direct GFP to the plasma membrane, while the regions containing less repetitive motifs, i.e. 6, 4, 2 or single motif(s) led to predominantly intracellular localization. Agrobacterium-mediated transient expression of PPC-GFP fusion protein further confirms the membrane-targeting capacities of PPC region. In addition, the predominant plasma membrane localization of AtPI4Kb was mediated by the PPC region. Recombinant PPC peptide, expressed in E. coli, strongly binds phosphatidic acid, PI and PI4P, but not phosphatidylcholine, PI5P, or PI(4,5) P-2 in vitro, providing insights into potential mechanisms for regulating sub- cellular localization and lipid binding for the plant beta-type PI4Ks Y1 - 2006 UR - http://www.springerlink.com/content/100330 U6 - https://doi.org/10.1007/s11103-005-5548-x SN - 0167-4412 ER - TY - JOUR A1 - Skirycz, Aleksandra A1 - Reichelt, Michael A1 - Burow, Meike A1 - Birkemeyer, Claudia Sabine A1 - Rolcik, Jacub A1 - Kopka, Joachim A1 - Zanor, Maria Ines A1 - Gershenzon, Jonathan A1 - Strnad, Miroslav A1 - Szopa, Jan A1 - Müller-Röber, Bernd A1 - Witt, Isabell T1 - DOF transcription factor AtDof1.1 (OBP2) is part of a regulatory network controlling glucosinolate biosynthesis in Arabidopsis N2 - Glucosinolates are a group of secondary metabolites that function as defense substances against herbivores and micro-organisms in the plant order Capparales. Indole glucosinolates (IGS), derivatives of tryptophan, may also influence plant growth and development. In Arabidopsis thaliana, indole-3-acetaldoxime (IAOx) produced from tryptophan by the activity of two cytochrome P450 enzymes, CYP79B2 and CYP79B3, serves as a precursor for IGS biosynthesis but is also an intermediate in the biosynthetic pathway of indole-3-acetic acid (IAA). Another cytochrome P450 enzyme, CYP83B1, funnels IAOx into IGS. Although there is increasing information about the genes involved in this biochemical pathway, their regulation is not fully understood. OBP2 has recently been identified as a member of the DNA-binding-with-one- finger (DOF) transcription factors, but its function has not been studied in detail so far. Here we report that OBP2 is expressed in the vasculature of all Arabidopsis organs, including leaves, roots, flower stalks and petals. OBP2 expression is induced in response to a generalist herbivore, Spodoptera littoralis, and by treatment with the plant signalling molecule methyl jasmonate, both of which also trigger IGS accumulation. Constitutive and inducible over- expression of OBP2 activates expression of CYP83B1. In addition, auxin concentration is increased in leaves and seedlings of OBP2 over-expression lines relative to wild-type, and plant size is diminished due to a reduction in cell size. RNA interference-mediated OBP2 blockade leads to reduced expression of CYP83B1. Collectively, these data provide evidence that OBP2 is part of a regulatory network that regulates glucosinolate biosynthesis in Arabidopsis Y1 - 2006 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2006.02767.x/full ER - TY - JOUR A1 - Kreft, Oliver A1 - Georgieva, Radostina A1 - Bäumler, Hans A1 - Steup, Martin A1 - Müller-Röber, Bernd A1 - Sukhorukov, Gleb B. A1 - Möhwald, Helmuth T1 - Red blood cell templated polyelectrolyte capsules : a novel vehicle for the stable encapsulation of DNA and proteins N2 - A novel method for the encapsulation of biomacromolecules, such as nucleic acids and proteins, into polyelectrolyte microcapsules is described. Fluorescence-labelled double-stranded DNA and human serum albumin (HSA) are used as model substances for encapsulation in hollow microcapsules templated on human erythrocytes. The encapsulation procedure involves an intermediate drying C, step. The accumulation of DNA and HSA in the capsules is observed by confocal laser scanning microscopy, UV spectroscopy, and flourimetry. The mechanism of encapsulation is discussed Y1 - 2006 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270 U6 - https://doi.org/10.1002/marc.200500777 SN - 1022-1336 ER - TY - JOUR A1 - Gliwicka, Marta A1 - Balazadeh, Salma A1 - Caldana, Camila A1 - Müller-Röber, Bernd A1 - Gaj, Malgorzata D. T1 - The use of multi-qPCR platform and tan1 mutant in identification of TF genes involved in somatic embryogenesis in Arabidopsis Y1 - 2009 UR - http://www.ib.uj.edu.pl/abc/index.php?d=06 SN - 0001-5296 ER - TY - JOUR A1 - Naso, Alessia A1 - Dreyer, Ingo A1 - Pedemonte, Laura A1 - Testa, Ilaria A1 - Gomez-Porras, Judith Lucia A1 - Usai, Cesare A1 - Müller-Röber, Bernd A1 - Diaspro, Alberto A1 - Gambale, Franco A1 - Picco, Cristiana T1 - The role of the C-terminus for functional heteromerization of the plant channel KDC1 N2 - Voltage-gated potassium channels are formed by the assembly of four identical (homotetramer) or different (heterotetramer) subunits. Tetramerization of plant potassium channels involves the C-terminus of the protein. We investigated the role of the C-terminus of KDC1, a Shaker-like inward-rectifying K+ channel that does not form functional homomeric channels, but participates in the formation of heteromeric complexes with other potassium alpha- subunits when expressed in Xenopus oocytes. The interaction of KDC1 with KAT1 was investigated using the yeast two- hybrid system, fluorescence and electrophysiological studies. We found that the KDC1-EGFP fusion protein is not targeted to the plasma membrane of Xenopus oocytes unless it is coexpressed with KAT1. Deletion mutants revealed that the KDC1 C- terminus is involved in heteromerization. Two domains of the C-terminus, the region downstream the putative cyclic nucleotide binding domain and the distal part of the C-terminus called K-HA domain, contributed to a different extent to channel assembly. Whereas the first interacting region of the C-terminus was necessary for channel heteromerization, the removal of the distal KHA domain decreased but did not abolish the formation of heteromeric complexes. Similar results were obtained when coexpressing KDC1 with the KAT1-homolog KDC2 from carrots, thus indicating the physiological significance of the KAT1/KDC1 characterization. Electrophysiological experiments showed furthermore that the heteromerization capacity of KDC1 was negatively influenced by the presence of the enhanced green fluorescence protein fusion. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00063495 U6 - https://doi.org/10.1016/j.bpj.2009.02.055 SN - 0006-3495 ER - TY - JOUR A1 - Gajdanowicz, Pawel A1 - Garcia-Mata, Carlos A1 - Gonzalez, Wendy A1 - Morales-Navarro, Samuel Elïas A1 - Sharma, Tripti A1 - Gonzalez-Nilo, Fernando Danilo A1 - Gutowicz, Jan A1 - Müller-Röber, Bernd A1 - Blatt, Michael R. A1 - Dreyer, Ingo T1 - Distinct roles of the last transmembrane domain in controlling Arabidopsis K+ channel activity N2 - The family of voltage-gated potassium channels in plants presumably evolved from a common ancestor and includes both inward-rectifying (K-in) channels that allow plant cells to accumulate K+ and outward-rectifying (K-out) channels that mediate K+ efflux. Despite their close structural similarities, the activity of Kin channels is largely independent of K+ and depends only on the transmembrane voltage, whereas that of K-out channels responds to the membrane voltage and the prevailing extracellular K+ concentration. Gating of potassium channels is achieved by structural rearrangements within the last transmembrane domain (S6). Here we investigated the functional equivalence of the S6 helices of the Kin channel KAT1 and the K-out channel SKOR by domain-swapping and site-directed mutagenesis. Channel mutants and chimeras were analyzed after expression in Xenopus oocytes. We identified two discrete regions that influence gating differently in both channels, demonstrating a lack of functional complementarity between KAT1 and SKOR. Our findings are supported by molecular models of KAT1 and SKOR in the open and closed states. The role of the S6 segment in gating evolved differently during specialization of the two channel subclasses, posing an obstacle for the transfer of the K+-sensor from K-out to K-in channels. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0028-646X U6 - https://doi.org/10.1111/j.1469-8137.2008.02749.x SN - 0028-646X ER - TY - JOUR A1 - Müller-Röber, Bernd A1 - Arvidsson, Samuel Janne T1 - Fertility control : the role of magnesium transporters in pollen development Y1 - 2009 UR - http://www.nature.com/cr/archive/index.html U6 - https://doi.org/10.1038/Cr.2009.82 SN - 1001-0602 ER -