bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification and Characterization of a Ca2+-Dependent Actin Filament-Severing Protein from Lily Pollen
Authors: Fan Xiaoxue , Hou Jian , Chen Xiaoliang , Chaudhry Faisal , Staiger Christopher J. , Ren Haiyun 
Published: December 2004

AbstractIt is well known that a tip-focused intracellular Ca2+ gradient and the meshwork of short actin filaments at the tip region are necessary for pollen tube growth. However, little is known about the connections between the two factors. Here, a novel Ca2+-dependent actin-binding protein with molecular mass of 41 kD from lily (Lilium davidii) pollen (LdABP41) was isolated and purified with DNase I chromatography. Our purification procedure yielded about 0.6 mg of LdABP41 with &gt;98% purity from 10 g of lily pollen. At least two isoforms with isoelectric points of 5.8 and 6.0 were detected on two-dimensional gels. The results of N-terminal sequencing and mass-spectrometry analysis of LdABP41 showed that both isoforms shared substantial similarity with trumpet lily (Lilium longiflorum) villin and other members of the gelsolin superfamily. Negative-stained electron microscope images showed that LdABP41 severed in vitro-polymerized lily pollen F-actin into short actin filaments in a Ca2+-sensitive manner. Microinjection of the anti-LdABP41 antibody into germinated lily pollen demonstrated that the protein was required for pollen tube growth. The results of immunolocalization of the protein showed that it existed in the cytoplasm of the pollen tube, especially focused in the tip region. Our results suggest that LdABP41 belongs to the gelsolin superfamily and may play an important role in controlling actin organization in the pollen tube tip by responding to the oscillatory, tip-focused Ca2+ gradient.
Analysis of Sequence, Map Position, and Gene Expression Reveals Conserved Essential Genes for Iron Uptake in Arabidopsis and Tomato
Authors: Bauer Petra , Thiel Thomas , Klatte Marco , Bereczky Zsolt , Brumbarova Tzvetina , Hell Rüdiger , Grosse Ivo 
Published: December 2004

Abstract
Arabidopsis (Arabidopsis thaliana) and tomato (Lycopersicon esculentum) show similar physiological responses to iron deficiency, suggesting that homologous genes are involved. Essential gene functions are generally considered to be carried out by orthologs that have remained conserved in sequence and map position in evolutionarily related species. This assumption has not yet been proven for plant genomes that underwent large genome rearrangements. We addressed this question in an attempt to deduce functional gene pairs for iron reduction, iron transport, and iron regulation between Arabidopsis and tomato. Iron uptake processes are essential for plant growth. We investigated iron uptake gene pairs from tomato and Arabidopsis, namely sequence, conserved gene content of the regions containing iron uptake homologs based on conserved orthologous set marker analysis, gene expression patterns, and, in two cases, genetic data. Compared to tomato, the Arabidopsis genome revealed more and larger gene families coding for the iron uptake functions. The number of possible homologous pairs was reduced if functional expression data were taken into account in addition to sequence and map position. We predict novel homologous as well as partially redundant functions of ferric reductase-like and iron-regulated transporter-like genes in Arabidopsis and tomato. Arabidopsis nicotianamine synthase genes encode a partially redundant family. In this study, Arabidopsis gene redundancy generally reflected the presumed genome duplication structure. In some cases, statistical analysis of conserved gene regions between tomato and Arabidopsis suggested a common evolutionary origin. Although involvement of conserved genes in iron uptake was found, these essential genes seem to be of paralogous rather than orthologous origin in tomato and Arabidopsis.
Short-Day Potentiation of Low Temperature-Induced Gene Expression of a C-Repeat-Binding Factor-Controlled Gene during Cold Acclimation in Silver Birch
Authors: Puhakainen Tuula , Li Chunyang , Boije-Malm Maria , Kangasjärvi Jaakko , Heino Pekka , Palva E. Tapio 
Published: December 2004

Abstract
Development of winter hardiness in trees is a two-stage process involving sequential perception of distinct environmental cues, short-day (SD) photoperiod and low temperature (LT). We have shown that both SD and LT are recognized by leaves of silver birch (Betula pendula cv Roth) leading to increased freezing tolerance, and thus leaves can be used as an experimental model to study the physiological and molecular events taking place during cold acclimation. To obtain a molecular marker for the acclimation process in birch we cloned a gene, designated Bplti36, encoding a 36-kD acidic SK2 type of dehydrin. The gene was responsive to LT, drought, salt, and exogenous abscisic acid. This responsiveness to abiotic stresses and abscisic acid was retained when Bplti36 was introduced to Arabidopsis (Arabidopsis thaliana). The LT induction of the gene appeared to be under the control of the C-repeat-binding factor pathway as suggested by the presence of several C-repeat/dehydration-responsive element/LT-responsive elements in the Bplti36 promoter and its constitutive expression in C-repeat-binding factor overproducing Arabidopsis. In birch SD photoperiod at normal-growth temperature did not result in significant induction of Bplti36. However, preexposure to SD followed by LT treatment resulted in a remarkable increase in Bplti36 transcript accumulation as compared to LT-treated plants grown at long-day photoperiod. This suggests that SD photoperiod potentiates the LT response by conditioning the leaf tissue to be more responsive to the LT stimulus.
Glutamate Dehydrogenase of Tobacco Is Mainly Induced in the Cytosol of Phloem Companion Cells When Ammonia Is Provided Either Externally or Released during Photorespiration
Authors: Tercé-Laforgue Thérèse , Dubois Frédéric , Ferrario-Méry Sylvie , Pou de Crecenzo Marie-Anne , Sangwan Rajbir , Hirel Bertrand 
Published: December 2004

Abstract
Glutamate (Glu) dehydrogenase (GDH) catalyses the reversible amination of 2-oxoglutarate for the synthesis of Glu using ammonium as a substrate. This enzyme preferentially occurs in the mitochondria of companion cells of a number of plant species grown on nitrate as the sole nitrogen source. For a better understanding of the controversial role of GDH either in ammonium assimilation or in the supply of 2-oxoglutarate (F. Dubois, T. Tercé-Laforgue, M.B. Gonzalez-Moro, M.B. Estavillo, R. Sangwan, A. Gallais, B. Hirel [2003] Plant Physiol Biochem 41: 565–576), we studied the localization of GDH in untransformed tobacco (Nicotiana tabacum) plants grown either on low nitrate or on ammonium and in ferredoxin-dependent Glu synthase antisense plants. Production of GDH and its activity were strongly induced when plants were grown on ammonium as the sole nitrogen source. The induction mainly occurred in highly vascularized organs such as stems and midribs and was likely to be due to accumulation of phloem-translocated ammonium in the sap. GDH induction occurred when ammonia was applied externally to untransformed control plants or resulted from photorespiratory activity in transgenic plants down-regulated for ferredoxin-dependent Glu synthase. GDH was increased in the mitochondria and appeared in the cytosol of companion cells. Taken together, our results suggest that the enzyme plays a dual role in companion cells, either in the mitochondria when mineral nitrogen availability is low or in the cytosol when ammonium concentration increases above a certain threshold.
Extracellular Calmodulin-Induced Stomatal Closure Is Mediated by Heterotrimeric G Protein and H2O2
Authors: Chen Yu-Ling , Huang Rongfeng , Xiao Yu-Mei , Lü Pin , Chen Jia , Wang Xue-Chen 
Published: December 2004

Abstract
Extracellular calmodulin (ExtCaM) exerts multiple functions in animals and plants, but the mode of ExtCaM action is not well understood. In this paper, we provide evidence that ExtCaM stimulates a cascade of intracellular signaling events to regulate stomatal movement. Analysis of the changes of cytosolic free Ca2+ ([Ca2+]cyt) and H2O2 in Vicia faba guard cells combined with epidermal strip bioassay suggests that ExtCaM induces an increase in both H2O2 levels and [Ca2+]cyt, leading to a reduction in stomatal aperture. Pharmacological studies implicate heterotrimeric G protein in transmitting the ExtCaM signal, acting upstream of [Ca2+]cyt elevation, and generating H2O2 in guard cell responses. To further test the role of heterotrimeric G protein in ExtCaM signaling in stomatal closure, we checked guard cell responses in the Arabidopsis (Arabidopsis thaliana) Gα-subunit-null gpa1 mutants and cGα overexpression lines. We found that gpa1 mutants were insensitive to ExtCaM stimulation of stomatal closure, whereas cGα overexpression enhanced the guard cell response to ExtCaM. Furthermore, gpa1 mutants are impaired in ExtCaM induction of H2O2 generation in guard cells. Taken together, our results strongly suggest that ExtCaM activates an intracellular signaling pathway involving activation of a heterotrimeric G protein, H2O2 generation, and changes in [Ca2+]cyt in the regulation of stomatal movements.
Phenolic Profiling of Caffeic Acid O-Methyltransferase-Deficient Poplar Reveals Novel Benzodioxane Oligolignols
Authors: Morreel Kris , Ralph John , Lu Fachuang , Goeminne Geert , Busson Roger , Herdewijn Piet , Goeman Jan L. , Van der Eycken Johan , Boerjan Wout , Messens Eric 
Published: December 2004

Abstract
Caffeic acid O-methyltransferase (COMT) catalyzes preferentially the methylation of 5-hydroxyconiferaldehyde to sinapaldehyde in monolignol biosynthesis. Here, we have compared HPLC profiles of the methanol-soluble phenolics fraction of xylem tissue from COMT-deficient and control poplars (Populus spp.), using statistical analysis of the peak heights. COMT down-regulation results in significant concentration differences for 25 of the 91 analyzed peaks. Eight peaks were exclusively detected in COMT-deficient poplar, of which four could be purified for further identification using mass spectrometry/mass spectrometry, nuclear magnetic resonance, and spiking of synthesized reference compounds. These new compounds were derived from 5-hydroxyconiferyl alcohol or 5-hydroxyconiferaldehyde and were characterized by benzodioxane moieties, a structural type that is also increased in the lignins of COMT-deficient plants. One of these four benzodioxanes amounted to the most abundant oligolignol in the HPLC profile. Furthermore, all of the differentially accumulating oligolignols involving sinapyl units were either reduced in abundance or undetectable. The concentration levels of all identified oligolignols were in agreement with the relative supply of monolignols and with their chemical coupling propensities, which supports the random coupling hypothesis. Chiral HPLC analysis of the most abundant benzodioxane dimer revealed the presence of both enantiomers in equal amounts, indicating that they were formed by radical coupling reactions under simple chemical control rather than guided by dirigent proteins.
Metabolic Engineering of the Chloroplast Genome Using the Echerichia coli ubiC Gene Reveals That Chorismate Is a Readily Abundant Plant Precursor for p-Hydroxybenzoic Acid Biosynthesis
Authors: Viitanen Paul V. , Devine Andrew L. , Khan Muhammad Sarwar , Deuel Deborah L. , Van Dyk Drew E. , Daniell Henry 
Published: December 2004

Abstract
p-Hydroxybenzoic acid (pHBA) is the major monomer in liquid crystal polymers. In this study, the Escherichia coli ubiC gene that codes for chorismate pyruvate-lyase (CPL) was integrated into the tobacco (Nicotiana tabacum) chloroplast genome under the control of the light-regulated psbA 5′ untranslated region. CPL catalyzes the direct conversion of chorismate, an important branch point intermediate in the shikimate pathway that is exclusively synthesized in plastids, to pHBA and pyruvate. The leaf content of pHBA glucose conjugates in fully mature T1 plants exposed to continuous light (total pooled material) varied between 13% and 18% dry weight, while the oldest leaves had levels as high as 26.5% dry weight. The latter value is 50-fold higher than the best value reported for nuclear-transformed tobacco plants expressing a chloroplast-targeted version of CPL. Despite the massive diversion of chorismate to pHBA, the plastid-transformed plants and control plants were indistinguishable. The highest CPL enzyme activity in pooled leaf material from adult T1 plants was 50,783 pkat/mg of protein, which is equivalent to approximately 35% of the total soluble protein and approximately 250 times higher than the highest reported value for nuclear transformation. These experiments demonstrate that the current limitation for pHBA production in nuclear-transformed plants is CPL enzyme activity, and that the process becomes substrate-limited only when the enzyme is present at very high levels in the compartment of interest, such as the case with plastid transformation. Integration of CPL into the chloroplast genome provides a dramatic demonstration of the high-flux potential of the shikimate pathway for chorismate biosynthesis, and could prove to be a cost-effective route to pHBA. Moreover, exploiting this strategy to create an artificial metabolic sink for chorismate could provide new insight on regulation of the plant shikimate pathway and its complex interactions with downstream branches of secondary metabolism, which is currently poorly understood.
Organization of Monoterpene Biosynthesis in Mentha. Immunocytochemical Localizations of Geranyl Diphosphate Synthase, Limonene-6-Hydroxylase, Isopiperitenol Dehydrogenase, and Pulegone Reductase
Authors: Turner Glenn W. , Croteau Rodney 
Published: December 2004

Abstract
We present immunocytochemical localizations of four enzymes involved in p-menthane monoterpene biosynthesis in mint: the large and small subunits of peppermint (Mentha x piperita) geranyl diphosphate synthase, spearmint (Mentha spicata) (−)-(4S)-limonene-6-hydroxylase, peppermint (−)-trans-isopiperitenol dehydrogenase, and peppermint (+)-pulegone reductase. All were localized to the secretory cells of peltate glandular trichomes with abundant labeling corresponding to the secretory phase of gland development. Immunogold labeling of geranyl diphosphate synthase occurred within secretory cell leucoplasts, (−)-4S-limonene-6-hydroxylase labeling was associated with gland cell endoplasmic reticulum, (−)-trans-isopiperitenol dehydrogenase labeling was restricted to secretory cell mitochondria, while (+)-pulegone reductase labeling occurred only in secretory cell cytoplasm. We discuss this pathway compartmentalization in relation to possible mechanisms for the intracellular movement of monoterpene metabolites, and for monoterpene secretion into the extracellular essential oil storage cavity.
Rice Contains Two Disparate ent-Copalyl Diphosphate Synthases with Distinct Metabolic Functions
Authors: Prisic Sladjana , Xu Meimei , Wilderman P. Ross , Peters Reuben J. 
Published: December 2004

Abstract
Rice (Oryza sativa) produces ent-copalyl diphosphate for both gibberellin (GA) phytohormone and defensive phytoalexin biosynthesis, raising the question of how this initial biosynthetic step is carried out for these distinct metabolic processes. Here, a functional genomics approach has been utilized to identify two disparate ent-copalyl diphosphate synthases from rice (OsCPS1ent and OsCPS2ent). Notably, it was very recently demonstrated that only one of these (OsCPS1ent) normally operates in GA biosynthesis as mutations in this gene result in severely impaired growth. Evidence is presented here strongly indicating that the other (OsCPS2ent) is involved in related secondary metabolism producing defensive phytochemicals. In particular, under appropriate conditions, OsCPS2ent mRNA is specifically induced in leaves prior to production of the corresponding phytoalexins. Thus, transcriptional control of OsCPS2ent seems to be an important means of regulating defensive phytochemical biosynthesis. Finally, OsCPS1ent is significantly more similar to the likewise GA-specific gene An1/ZmCPS1ent in maize (Zea mays) than its class II terpene synthase paralogs involved in rice secondary metabolism. Hence, we speculate that this cross-species conservation by biosynthetic process reflects derivation of related secondary metabolism from the GA primary biosynthetic pathway prior to the early divergence between the separate lineages within the cereal/grass family (Poaceae) resulting in modern rice and maize.
Green Fluorescent Protein-mTalin Causes Defects in Actin Organization and Cell Expansion in Arabidopsis and Inhibits Actin Depolymerizing Factor's Actin Depolymerizing Activity in Vitro
Authors: Ketelaar Tijs , Anthony Richard G. , Hussey Patrick J. 
Published: December 2004

Abstract
Expression of green fluorescent protein (GFP) linked to an actin binding domain is a commonly used method for live cell imaging of the actin cytoskeleton. One of these chimeric proteins is GFP-mTalin (GFP fused to the actin binding domain of mouse talin). Although it has been demonstrated that GFP-mTalin colocalizes with the actin cytoskeleton, its effect on actin dynamics and cell expansion has not been studied in detail. We created Arabidopsis (Arabidopsis thaliana) plants harboring alcohol inducible GFP-mTalin constructs to assess the effect of GFP-mTalin expression in vivo. We focused on the growing root hair as this is a model cell for studying cell expansion and root hair tip growth that requires a highly dynamic and polar actin cytoskeleton. We show that alcohol inducible expression of GFP-mTalin in root hairs causes severe defects in actin organization, resulting in either the termination of growth, cell death, and/or changes in cell shape. Fluorescence recovery after photobleaching experiments demonstrate that the interaction of GFP-mTalin and actin filaments is highly dynamic. To assess how GFP-mTalin affects actin dynamics we performed cosedimentation assays of GFP-mTalin with actin on its own or in the presence of the actin modulating protein, actin depolymerizing factor. We show that that GFP-mTalin does not affect actin polymerization but that it does inhibit the actin depolymerizing activity of actin depolymerizing factor. These observations demonstrate that GFP-mTalin can affect cell expansion, actin organization, and the interaction of actin binding proteins with actin.
The Role of Aquaporins and Membrane Damage in Chilling and Hydrogen Peroxide Induced Changes in the Hydraulic Conductance of Maize Roots
Authors: Aroca Ricardo , Amodeo Gabriela , Fernández-Illescas Silvia , Herman Eliot M. , Chaumont François , Chrispeels Maarten J. 
Published: December 2004

Abstract
When chilling-sensitive plants are chilled, root hydraulic conductance (L o) declines precipitously; L o also declines in chilling-tolerant plants, but it subsequently recovers, whereas in chilling-sensitive plants it does not. As a result, the chilling-sensitive plants dry out and may die. Using a chilling-sensitive and a chilling-tolerant maize genotype we investigated the effect of chilling on L o, and its relationship to osmotic water permeability of isolated root cortex protoplasts, aquaporin gene expression, aquaporin abundance, and aquaporin phosphorylation, hydrogen peroxide (H2O2) accumulation in the roots and electrolyte leakage from the roots. Because chilling can cause H2O2 accumulation we also determined the effects of a short H2O2 treatment of the roots and examined the same parameters. We conclude from these studies that the recovery of L o during chilling in the chilling-tolerant genotype is made possible by avoiding or repairing membrane damage and by a greater abundance and/or activity of aquaporins. The same changes in aquaporins take place in the chilling-sensitive genotype, but we postulate that membrane damage prevents the L o recovery. It appears that the aquaporin response is necessary but not sufficient to respond to chilling injury. The plant must also be able to avoid the oxidative damage that accompanies chilling.
Progression through Meiosis I and Meiosis II in Arabidopsis Anthers Is Regulated by an A-Type Cyclin Predominately Expressed in Prophase I
Authors: Wang Yixing , Magnard Jean-Louis , McCormick Sheila , Yang Ming 
Published: December 2004

Abstract
Meiosis is often described as a special case of cell division since it differs from mitosis in having two nuclear divisions without an intervening S-phase. It will be of great interest to uncover what molecular mechanisms underlie these special features of meiosis. We previously reported that the tardy asynchronous meiosis (tam) mutant of Arabidopsis (Arabidopsis thaliana) is slower in cell cycle progression in male meiosis. Here we report that TAM encodes the A-type cyclin, CYCA1;2. The point mutation in tam replaced a conserved threonine with an isoleucine in the linker region between the α4 and α5 helices of the first cyclin fold. By studying the dynamics of a CYCA1;2-green fluorescent protein fusion protein under the control of the CYCA1;2 promoter, we found that the fusion protein was most abundant at pachytene, but was undetectable from late prophase I until telophase II. Nonetheless, cell cycle progression in tam was delayed in both pachytene and meiosis II. We conclude either that the CYCA1;2 produced in prophase I indirectly regulates meiosis II progression, or that a very low level of CYCA1;2 directly regulates meiosis II progression. Either of these scenarios is a deviation from the typical mode of action of mitotic cyclins in mitosis and meiosis I, in which each nuclear division is coupled with a peak of expression of mitotic cyclins.
Efficient Virus-Induced Gene Silencing in Roots Using a Modified Tobacco Rattle Virus Vector
Authors: Valentine Tracy , Shaw Jane , Blok Vivian C. , Phillips Mark S. , Oparka Karl J. , Lacomme Christophe 
Published: December 2004

Abstract
Due to their capability of eliciting a form of posttranscriptional gene silencing (termed virus-induced gene silencing or VIGS), plant viruses are increasingly used as reverse-genetics tools for functional characterization of plant genes. RNA viruses have been shown to trigger silencing in a variety of host plants, including members of Solanacae and Arabidopsis (Arabidopsis thaliana). Several factors affect the silencing response, including host range and viral tropism within the plant. The work presented here demonstrates that a modified tobacco rattle virus (TRV) vector retaining the helper protein 2b, required for transmission by a specific vector nematode, not only invades and replicates extensively in whole plants, including meristems, but also triggers a pervasive systemic VIGS response in the roots of Nicotiana benthamiana, Arabidopsis, and tomato (Lycopersicon esculentum). This sustained VIGS response was exemplified by the silencing of genes involved in root development (IRT1, TTG1 [transparent testa glabra], RHL1 [root hairless1], and β-tubulin), lateral root-meristem function (RML1 [root meristemless1]), and nematode resistance (Mi). Roots of silenced plants exhibit reduced levels of target mRNA and phenocopy previously described mutant alleles. The TRV-2b vector displays increased infectivity and meristem invasion, both key requirements for efficient VIGS-based functional characterization of genes in root tissues. Our data suggest that the TRV helper protein 2b may have an essential role in the host regulatory mechanisms that control TRV invasion.