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J. A. Banks,
T. Nishiyama,
M. Hasebe,
J. L. Bowman,
M. Gribskov,
C. Depamphilis,
V. A. Albert,
N. Aono,
T. Aoyama,
B. A. Ambrose, [......],
U. Hellsten,
D. Loque,
R. Otillar,
A. Salamov,
J. Schmutz,
H. Shapiro,
E. Lindquist,
S. Lucas,
D. Rokhsar,
I. V. Grigoriev
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ABSTRACT: Vascular plants appeared ~410 million years ago, then diverged into several lineages, of which only two survive: the euphyllophytes(ferns and seed plants) and the lycophytes. Here, we report the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionary diverse taxa, we found that the transition from a gametophyte- to sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, while secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the tasiRNA pathway and extensive RNA editing of organellar genes.
Science. 01/2011; 5:5.
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ABSTRACT: The group of voltage-independent K(+) channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1-TPK5) and a single K(ir)-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein-protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels.
Plant Biology 09/2010; 12 Suppl 1:56-63. · 2.39 Impact Factor
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ABSTRACT: The family of voltage-gated (Shaker-like) potassium channels in plants includes both inward-rectifying (Kin) channels that allow plant cells to accumulate K<sup>+</sup> and outward-rectifying (K<sub>out</sub>) channels that mediate K<sup>+</sup> efflux. Despite their close structural similarities, Kin and Kout channels differ in their gating sensitivity towards voltage and the extracellular K<sup>+</sup> concentration. We have carried out a systematic program of domain swapping between the K<sub>out</sub> channel SKOR and the Kin channel KAT1 to examine the impacts on gating of the pore regions, the S4, S5, and the S6 helices. We found that, in particular, the N-terminal part of the S5 played a critical role in KAT1 and SKOR gating. Our findings were supported by molecular dynamics of KAT1 and SKOR homology models. In silico analysis revealed that during channel opening and closing, displacement of certain residues, especially in the S5 and S6 segments, is more pronounced in KAT1 than in SKOR. From our analysis of the S4-S6 region, we conclude that gating (and K <sup>+</sup>-sensing in SKOR) depend on a number of structural elements that are dispersed over this ∼145-residue sequence and that these place additional constraints on configurational rearrangement of the channels during gating.
Molecular Plant. 01/2010; 3(1):236-245.
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ABSTRACT: Senescence is a highly regulated process, eventually leading to cell and tissue disintegration: a physiological process associated with nutrient (e.g. nitrogen) redistribution from leaves to reproductive organs. Senescence is not observed in young leaves, indicating that repressors efficiently act to suppress cell degradation during early leaf development and/or that senescence activators are switched on when a leaf ages. Thus, massive regulatory network re-wiring likely constitutes an important component of the pre-senescence process. Transcription factors (TFs) have been shown to be central elements of such regulatory networks. Here, we used quantitative real-time polymerase chain reaction (qRT-PCR) analysis to study the expression of 1880 TF genes during pre-senescence and early-senescence stages of leaf development, using Arabidopsis thaliana as a model. We show that the expression of 185 TF genes changes when leaves develop from half to fully expanded leaves and finally enter partial senescence. Our analysis identified 41 TF genes that were gradually up-regulated as leaves progressed through these developmental stages. We also identified 144 TF genes that were down-regulated during senescence. A considerable number of the senescence-regulated TF genes were found to respond to abiotic stress, and salt stress appeared to be the major factor controlling their expression. Our data indicate a peculiar fine-tuning of developmental shifts during late-leaf development that is controlled by TFs.
Plant Biology 09/2008; 10 Suppl 1:63-75. · 2.39 Impact Factor
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ABSTRACT: Leaf senescence is a developmentally regulated process that contributes to nutrient redistribution during reproductive growth and finally leads to tissue death. Manipulating leaf senescence through breeding or genetic engineering may help to improve important agronomic traits, such as crop yield and the storage life of harvested organs. Here, we studied natural variations in the regulation of plant senescence among 16 Arabidopsis thaliana accessions. Chlorophyll content and the proportion of yellow leaves were used as indicator parameters to determine leaf and plant senescence respectively. Our study indicated significant genotype effects on the onset and development of senescence. We selected three late- and five early-senescence accessions for further physiological studies. The relationship between leaf and plant senescence was accession-dependent. There was a significant correlation between plant senescence and the total number of leaves, siliques and plant bolting age. We monitored expression of two senescence marker genes, SAG12 and WRKY53, to evaluate progression of senescence. Our data revealed that chlorophyll content does not fully reflect leaf age, because even fully green leaves had already commenced senescence at the molecular level. Integrating senescence parameters, such as the proportion of senescent leaves, at the whole plant level provided a better indication of the molecular status of the plant than single leaf senescence parameters.
Plant Biology 09/2008; 10 Suppl 1:136-47. · 2.39 Impact Factor
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D Becker,
D Geiger,
M Dunkel,
A Roller,
A Bertl,
A Latz,
A Carpaneto,
P Dietrich,
M R G Roelfsema,
C Voelker,
D Schmidt, B Mueller-Roeber,
K Czempinski,
R Hedrich
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ABSTRACT: 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.
Proceedings of the National Academy of Sciences 12/2004; 101(44):15621-6. · 9.68 Impact Factor
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ABSTRACT: An appreciable number of potassium channels mediating K+ uptake have been identified in higher plants. Promoter-beta-glucuronidase reporter gene studies were used here to demonstrate that SKT1, encoding a potato K+ inwardly rectifying channel, is expressed in guard cells in addition to KST1 previously reported. However, whereas KST1 was found to be expressed in essentially all mature guard cells, SKT1 expression was almost exclusively restricted to guard cells of the abaxial leaf epidermis. This suggests that different types of K+ channel subunits contribute to channel formation in potato guard cells and therefore differential regulation of stomatal movements in the two leaf surfaces. The overlapping expression pattern of SKT1 and KST1 in abaxial guard cells indicates that K+in channels of different sub-families contribute to ionic currents in this cell type, thus explaining the different properties of channels expressed solely in heterologous systems and those endogenous to guard cells. Interaction studies had previously suggested that plant K+ inward rectifiers form clusters via their conserved C-terminal domain, KT/HA. K+ channels co-expressed in one cell type may therefore form heteromers, which increase functional variability of K+ currents, a phenomenon well described for animal voltage-gated K+ channels. Co-expression of KST1 and SKT1 in Xenopus oocytes resulted in currents with an intermediate sensitivity towards Cs+, suggesting the presence of heteromers, and a sensitivity towards external Ca2+, which reflected the property of the endogenous K+in current in guard cells. Modulation of KST1 currents in oocytes by co-expressing KST1 with a SKT1 pore-mutant, which by itself was not able to confer activating K+ currents, demonstrated the possibility that KST1 and SKT1 co-assemble to hetero-oligomers. Furthermore, various C-terminal deletions of the mutated SKT1 channel restored KST1 currents, showing that the C-terminal KT motif is essential for heteromeric channel formation.
The Plant Journal 01/2002; 28(5):517-27. · 6.16 Impact Factor
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ABSTRACT: Due to their unique structure and function, guard cells have attracted much attention at the physiological level. Very little, however, is known about the molecular events involved in the determination and maintenance of guard cell specificity. The KST1 gene encodes a K+ influx channel of guard cells in potato, and was therefore chosen as a model to study regulation of guard cell-specific gene expression. Transgenic potato plants carrying a fusion between the KST1 promoter and the E. coli uidA (beta-glucuronidase) reporter gene revealed promoter activity in guard cells and in flowers. A detailed dissection of the KST1 promoter led to the discovery of two independent small TATA box-proximal regulatory units, each of which was sufficient to direct guard cell-specific gene transcription. Both fragments contain the sequence motif, 5'-TAAAG-3', which is related to known target sites for a novel class of zinc finger transcription factors, called Dof proteins. Block mutagenesis of these Dof target sites in the context of different promoter constructs dramatically reduced guard cell promoter activity. A Dof gene, StDof1, was cloned and shown to be expressed in epidermal fragments highly enriched for guard cells. In gel retardation experiments, the StDof1 protein interacted in a sequence-specific manner with a KST1 promoter fragment containing the TAAAG motif. These results provide evidence that TAAAG elements are target sites for trans-acting Dof proteins controlling guard cell-specific gene expression. Our data will add to the design of tailor-made guard cell promoters as a further tool in molecular engineering of guard cell function and, hence, control of stomatal carbon dioxide (CO2) uptake and water loss in crop plants.
The Plant Journal 12/2001; 28(4):455-64. · 6.16 Impact Factor
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ABSTRACT: We have cloned a phosphatidylinositol-4-phosphate 5-kinase (PIP5K) cDNA (AtP5K1) from Arabidopsis thaliana. By the application of cell permeabilization and short-term nonequilibrium labelling we show that expression of AtP5K1 in Baculovirus-infected insect (Spodoptera frugiperda) cells directs synthesis of PtdIns(4,5)P2 and PtdIns(3,4,5)P3. The same phosphoinositides were produced by isolated whole-cell membrane fractions of AtP5K1-expressing insect cells. Their synthesis was not affected by adding defined precursor lipids, that is PtdIns(3)P, PtdIns(4)P, PtdIns(3,4)P2, or PtdIns(4,5)P2, in excess, indicating that substrates for the plant enzyme were not limiting in vivo. Enzymatic dissection of lipid headgroups revealed that AtP5K1-directed synthesis of PtdIns(4,5)P2 and PtdIns(3,4,5)P3 proceeds via 5-phosphorylation of precursors. Analysis of promoter-reporter gene (beta-glucuronidase) fusions in transgenic plants revealed that expression of the AtP5K1 gene is strongest in vascular tissues of leaves, flowers, and roots, namely in cells of the lateral meristem, that is the procambium. Single-cell sampling of sap from flower stem meristem tissue and neighbouring phloem cells, when coupled to reverse transcriptase--polymerase chain reaction, confirmed preferential expression of AtP5K1 in procambial tissue. We hypothesize that AtP5K1, like animal and yeast PIP5K, may be involved in the control of cell proliferation.
The Plant Journal 07/2001; 26(6):561-71. · 6.16 Impact Factor
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N Gaedeke,
M Klein,
U Kolukisaoglu,
C Forestier,
A Müller,
M Ansorge,
D Becker,
Y Mamnun,
K Kuchler,
B Schulz, B Mueller-Roeber,
E Martinoia
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ABSTRACT: In the present study, we investigated a new member of the ABC transporter superfamily of Arabidopsis thaliana, AtMRP5. AtMRP5 encodes a 167 kDa protein and exhibits low glutathione conjugate and glucuronide conjugate transport activity. Promotor- beta-glucuronidase fusion constructs showed that AtMRP5 is expressed mainly in the vascular bundle and in the epidermis, especially guard cells. Using reverse genetics, we identified a plant with a T-DNA insertion in AtMRP5 (mrp5-1). mrp5-1 exhibited decreased root growth and increased lateral root formation. Auxin levels in the roots of mrp5-1 plants were increased. This observation may indicate that AtMRP5 works as an auxin conjugate transporter or that mutant plants are affected in ion uptake, which may lead to changes in auxin concentrations. Experiments on epidermal strips showed that in contrast to wild type, the sulfonylurea glibenclamide had no effect on stomatal opening in mrp5-1 plants. This result strongly suggests that AtMRP5 may also function as an ion channel regulator.
The EMBO Journal 05/2001; 20(8):1875-87. · 9.20 Impact Factor
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ABSTRACT: This report describes the use of promoter trap lines from the model plant Arabidopsis thaliana to clone regulatory sequences that mediate guard-cell-specific reporter gene expression. Stomatal guard cells represent a highly differentiated cell type within the epidermis of green tissues of higher plants. They control the stomatal aperture in response to different endogenous and environmental signals in order to optimize carbon fixation while minimizing water loss. We screened available promoter trap lines for guard-cell-specific activation of a beta-glucuronidase (uidA) reporter gene in order to obtain marker lines for guard-cell development and to gain access to regulatory pathways leading to gene expression which is restricted to this cell type. From two lines identified we successfully cloned upstream regulatory sequences. For one line, guard-cell-specific promoter activity was confirmed by re-introducing the uidA gene, fused to the newly identified regulatory sequences, into the Arabidopsis nuclear genome. However, DNA sequences downstream of the uidA/T-DNA insertion sites in the original promoter trap lines revealed no obvious coding regions in the corresponding orientation, indicating that we have probably identified 'cryptic' promoters, being active in guard cells.
Gene 06/2000; 249(1-2):83-9. · 2.34 Impact Factor
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ABSTRACT: A cDNA encoding a novel inwardly rectifying potassium (K+(in)) channel, LKT1, was cloned from a root-hair-specific cDNA library of tomato (Lycopersicon esculentum Mill.). The LKT1 mRNA was shown to be most strongly expressed in root hairs by Northern blot analysis. The LKT1 channel is a member of the AKT family of K+(in) channels previously identified in Arabidopsis thaliana (L.) Heynh. and potato (Solanum tuberosum L.). Moreover, LKT1 is closely related (97% identical amino acids) to potato SKT1. An electrophysiological comparison of the two channels should therefore assist the identification of possible molecular bases for functional differences. For, this comparison, both channels were functionally expressed and electrophysiologically characterised within the same expression system, i.e. Xenopus laevis oocytes. Voltage-clamp measurements identified LKT1 as a K(+)-selective inward rectifier which activates with slow kinetics upon hyperpolarising voltage pulses to potentials more negative than -50 mV. The activation potential of LKT1 is shifted towards positive potentials with respect to SKT1 which might be due to single amino acid exchanges in the rim of the channel's pore region or in the S4 domain. Like SKT1, LKT1 reversibly activated upon shifting the external pH from 6.6 to 5.5, which indicates a physiological role for pH-dependent regulation of AKT-type K+(in) channels. The pharmacological inhibitor Cs+, applied externally, inhibited K+(in) currents mediated by LKT1 and SKT1 half-maximally with a concentration (IC50) of 21 microM and 17 microM, respectively. In conclusion, LKT1 may serve as a low-affinity influx pathway for K+ into root hair cells. Comparison of homologous K+(in) rectifiers from different plant species expressed in the same heterologous system allows conclusions to be drawn in respect to structure-function relationships.
Planta 05/2000; 210(5):723-31. · 3.00 Impact Factor
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ABSTRACT: Guard cells represent a highly differentiated cell type within the epidermis of plant leaves and stems. They respond to many endogenous and environmental signals and thereby modify the size of the stomatal pore they surround. We identified a novel gene that is highly expressed in guard cells of potato (Solanum tuberosum). It encodes a repetitive proline (Pro)-rich protein of 54 kD (491 amino acids) and was named StGCPRP (S. tuberosum guard cell Pro-rich protein). StGCPRP has a bipartite structure. The C-terminal part of StGCPRP contains a high percentage (46%) of Pro residues organized in distinct repetitive sequence motifs, whereas its extended N terminus is essentially free of Pros. StGCPRP represents the first member of a novel class of hybrid Pro-rich proteins that we designated NHyPRPs. In young but not in mature leaves, StGCPRP transcripts were also present at high levels in mesophyll cells (in addition to guard cells), indicating developmental regulation of StGCPRP gene expression. In addition, StGCPRP expression is regulated by environmental factors, as shown by a decrease in StGCPRP transcript levels under drought stress. Two proteins similar to StGCPRP were found to be encoded by the Arabidopsis genome, indicating that NHyPRPs are more widely distributed in higher plants.
Plant physiology 04/2000; 122(3):677-86. · 6.53 Impact Factor
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A. Skirycz,
A. Radziejwoski,
W. Busch,
M. A. Hannah,
J. Czeszejko,
M. Kwasniewski,
M. I. Zanor,
J. U. Lohmann,
L. De Veylder,
I. Witt, B. Mueller-Roeber
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ABSTRACT: In contrast to animal growth, plant growth is largely post-embryonic. Therefore plants have developed new mechanisms to precisely regulate cell proliferation by means of internal and external stimuli whilst the general core cell cycle machinery is conserved between eukaryotes. In this work we demonstrate a role for the Arabidopsis thaliana DNA-binding-with-one-finger (DOF) transcription factor OBP1 in the control of cell division upon developmental signalling. Inducible overexpression of OBP1 resulted in a significant overrepresentation of cell cycle genes among the upregulated transcripts. Direct targets of OBP1, as verified by chromatin immunoprecipitation, include at least the core cell cycle gene CYCD3;3 and the replication-specific transcription factor gene AtDOF2;3. Consistent with our molecular data, short-term activation of OBP1 in cell cultures affected cell cycle re-entry, shortening the duration of the G(1) phase and the overall length of the cell cycle, whilst constitutive overexpression of OBP1 in plants influenced cell size and cell number, leading to a dwarfish phenotype. Expression during embryogenesis, germination and lateral root initiation suggests an important role for OBP1 in cell cycle re-entry, operating as a transcriptional regulator of key cell cycle genes. Our findings provide significant input into our understanding of how cell cycle activity is incorporated into plant growth and development.
Plant J. 56(5):779-92.
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Genome Biology and Evolution, v.2, 488-503 (2010).
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Plant Journal, v.62, 250-264 (2010).
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Plant Signaling & Behavior, v.5, 733-735 (2010).
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Nucleic Acids Research, v.38, D822-D827 (2010).
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Molecular Plant, v.3, 236-245 (2010).
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A. Skirycz,
Michael Reichelt,
Meike Burow,
C. Birkemeyer,
J. Rolcik,
J. Kopka,
M. I. Zanor,
Jonathan Gershenzon,
M. Strnad,
J. Szopa, B Mueller-Roeber,
I. Witt
Plant Journal, v.47, 10-24 (2006).
