bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localization and control of expression of Nt‐Syr1, a tobacco snare protein
Authors: Leyman Barbara , Geelen Danny , Blatt Michael R. 
Published: March 2003

SummarySyntaxins and other SNARE proteins are crucial for intracellular vesicle trafficking, fusion and secretion. Previously, we isolated the syntaxin‐related protein Nt‐Syr1 from Nicotiana in a screen for ABA‐related signalling elements, and demonstrated its role in determining the ABA sensitivity of stomatal guard cells. Because the location and expression of SNAREs are often important clues to their functioning, we have examined the distribution and stimulus‐dependent expression of Nt‐Syr1 between tissues, as well as its location within the cell, using antisera raised against purified recombinant peptides corresponding to overlapping cytosolic domains of Nt‐Syr1. The Nt‐Syr1 epitope was strongly represented in roots and to lesser extents in stems, leaves and flowers of well‐watered plants. Biochemical analysis and examination of immunogold labelling under the electron microscope indicated Nt‐Syr1 to be located primarily at the plasma membrane. Expression of the protein in leaves and to a lesser extent in flowers and stems was transiently enhanced by ABA, but not by auxin, kinetin or gibberellic acid. Expression in leaves was promoted by salt stress and wounding, but not by cold. By contrast, Nt‐Syr1 levels in the root were unaffected by ABA. In the leaves, enhanced expression of Nt‐Syr1 by salt stress was not observed in aba1 mutant Nicotiana, which is deficient in ABA synthesis, and in plants carrying the Arabidopsis abi1 transgene that suppresses a number of ABA‐evoked responses in these plants. However, an enhanced expression in response to wounding was observed, even in the mutant backgrounds. We conclude that Nt‐Syr1 expression at the plasma membrane is important for its function and is subject to control by parallel, stress‐related signalling pathways, both dependent on and independent of ABA. Nt‐Syr1 may be associated with additional functions, especially in the roots, that are unrelated to ABA or stress responses in the plant.
Promotive effect of brassinosteroids on cell division involves a distinct CycD3‐induction pathway in Arabidopsis
Authors: Hu Yuxin , Bao Fang , Li Jiayang 
Published: March 2003

SummaryBrassinosteroids (BRs) are steroid hormones that play an essential role in plant growth and development. However, the contradictory results of previous studies make their role in cell division unclear. Using a cDNA array, we identified genes that respond to BR in the det2 suspension culture of Arabidopsis, and found that epi‐brassinolide upregulated transcription of the CycD3, a D‐type plant cyclin gene through which cytokinin activates cell division. RNA gel‐blot analysis and cell culturing showed that epi‐brassinolide may promote cell division through CycD3, and can substitute cytokinin in culturing of Arabidopsis callus and suspension cells. The CycD3 induction by epi‐brassinolide was further shown to involve de novo protein synthesis, but no protein phosphorylation or dephosphorylation. Induction was also found to occur in cells of a BR‐insensitive mutant, bri1, suggesting that BR induces CycD3 transcription through a previously unknown signal pathway in plants.
The ABI1 and ABI2 protein phosphatases 2C act in a negative feedback regulatory loop of the abscisic acid signalling pathway
Authors: Merlot Sylvain , Gosti Françoise , Guerrier Danièle , Vavasseur Alain , Giraudat Jérôme 
Published: March 2003

SummaryThe ArabidopsisABI1andABI2genes encode two protein serine/threonine phosphatases 2C (PP2C). These genes have been originally identified by the dominant mutationsabi1–1andabi2–1,which reduce the plant's responsiveness to the hormone abscisic acid (ABA). However, recessive mutants ofABI1were recently shown to be supersensitive to ABA, which demonstrated that the ABI1 phosphatase is a negative regulator of ABA signalling. We report here the isolation and characterisation of the first reduction‐of‐function allele ofABI2,abi2–1R1. Thein vitrophosphatase activity of the abi2–1R1 protein is approximately 100‐fold lower than that of the wild‐type ABI2 protein.Abi2–1R1plants displayed a wild‐type ABA sensitivity. However, doubly mutant plants combining theabi2–1R1allele and a loss‐of‐function allele at theABI1locus were more responsive to ABA than each of the parental single mutants. These data indicate that the wild‐type ABI2 phosphatase is a negative regulator of ABA signalling, and that the ABI1 and ABI2 phosphatases have overlapping roles in controlling ABA action. Measurements of PP2C activity in plant extracts showed that the phosphatase activity of ABI1 and ABI2 increases in response to ABA. These results suggest that ABI1 and ABI2 act in a negative feedback regulatory loop of the ABA signalling pathway.
Ethylene‐dependent salicylic acid regulates an expanded cell death response to a plant pathogen
Authors: O'Donnell Philip J. , Jones Jeffrey B. , Antoine Francis R. , Ciardi Joseph , Klee Harry J. 
Published: March 2003

SummaryThe molecular events associated with susceptible plant responses to disease‐causing organisms are not well understood. We have previously shown that ethylene‐insensitive tomato plants infected with Xanthomonas campestris pv. vesicatoria have greatly reduced disease symptoms relative to wild‐type cultivars. Here we show that salicylic acid (SA) is also an important component of the susceptible disease response. SA accumulates in infected wild‐type tissues and is correlated with necrosis but does not accumulate in ethylene‐insensitive plants. Exogenous feeding of SA to ethylene‐deficient plants restores necrosis, indicating that reduced disease symptoms are associated with failure to accumulate SA. These results indicate a mechanism for co‐ordination of phytohormone signals that together constitute a susceptible response to pathogens.
The ratio of campesterol to sitosterol that modulates growth in Arabidopsis is controlled by STEROL METHYLTRANSFERASE 2;1
Authors: Schaeffer Aurélie , Bronner Roberte , Benveniste Pierre , Schaller Hubert 
Published: March 2003

SummaryThe Arabidopsis genome contains three distinct genes encoding sterol‐C24‐methyltransferases (SMTs) involved in sterol biosynthesis. The expression of one of them, STEROL METHYLTRANSFERASE 2;1, was modulated in 35S::SMT2;1 Arabidopsis in order to study its physiological function. Plants overexpressing the transgene accumulate sitosterol, a 24‐ethylsterol which is thought to be the typical plant membrane reinforcer, at the expense of campesterol. These plants displayed a reduced stature and growth that could be restored by brassinosteroid treatment. Plants showing co‐suppression of SMT2;1 were characterized by a predominant 24‐methylsterol biosynthetic pathway leading to a high campesterol content and a depletion in sitosterol. Pleiotropic effects on development such as reduced growth, increased branching, and low fertility of high‐campesterol plants were not modified by exogenous brassinosteroids, indicating specific sterol requirements to promote normal development. Thus SMT2;1 has a crucial role in balancing the ratio of campesterol to sitosterol in order to fit both growth requirements and membrane integrity.
Expression of a plant gene with sequence similarity to animal TGF‐β receptor interacting protein is regulated by brassinosteroids and required for normal plant development
Authors: Jiang Jingrui , Clouse Steven D. 
Published: March 2003

SummaryBrassinosteroids (BRs) regulate the expression of numerous genes associated with plant development, and require the activity of a Ser/Thr receptor kinase to realize their effects. In animals, the transforming growth factor‐β (TGF‐β) family of peptides acts via Ser/Thr receptor kinases to have a major impact on several pathways involved in animal development and adult homeostasis. TGF‐β receptor‐interacting protein (TRIP‐1) was previously shown by others to be an intracellular substrate of the TGF‐β type II receptor kinase which plays an important role in TGF‐β signaling. TRIP‐1 is a WD‐repeat protein that also has a dual role as an essential subunit of the eukaryotic translation initiation factor eIF3 in animals, yeast and plants, thereby revealing a putative link between a developmental signaling pathway and the control of protein translation. In yeast, expression of a TRIP‐1 homolog has also been closely associated with cell proliferation and progression through the cell cycle. We report here the novel observation that transcript levels of TRIP‐1 homologs in plants are regulated by BR treatment under a variety of conditions, and that transgenic plants expressing antisense TRIP‐1 RNA exhibit a broad range of developmental defects, including some that resemble the phenotype of BR‐deficient and ‐insensitive mutants. This correlative evidence suggests that a WD‐domain protein with reported dual functions in vertebrates and fungi might mediate some of the molecular mechanisms underlying the regulation of plant growth and development by BRs.
Interaction of phytochromes A and B in the control of de‐etiolation and flowering in pea
Authors: Weller James L. , Beauchamp Nicola , Kerckhoffs L. Huub J. , Platten J. Damien , Reid James B. 
Published: March 2003

SummaryThe interactions of phytochrome A (phyA) and phytochrome B (phyB) in the photocontrol of vegetative and reproductive development in pea have been investigated using null mutants for each phytochrome. White‐light‐grown phyA phyB double mutant plants show severely impaired de‐etiolation both at the seedling stage and later in development, with a reduced rate of leaf production and swollen, twisted internodes, and enlarged cells in all stem tissues. PhyA and phyB act in a highly redundant manner to control de‐etiolation under continuous, high‐irradiance red light. The phyA phyB double mutant shows no significant residual phytochrome responses for either de‐etiolation or shade‐avoidance, but undergoes partial de‐etiolation in blue light. PhyB is shown to inhibit flowering under both long and short photoperiods and this inhibition is required for expression of the promotive effect of phyA. PhyA is solely responsible for the promotion of flowering by night‐breaks with white light, whereas phyB appears to play a major role in detection of light quality in end‐of‐day light treatments, night breaks and day extensions. Finally, the inhibitory effect of phyB is not graft‐transmissible, suggesting that phyB acts in a different manner and after phyA in the control of flower induction.
Evidence for a disease‐resistance pathway in rice similar to the NPR1‐mediated signaling pathway in Arabidopsis
Authors: Chern Maw‐Sheng , Fitzgerald Heather A. , Yadav Ram C. , Canlas Patrick E. , Dong Xinnian , Ronald Pamela C. 
Published: March 2003

SummaryThe Arabidopsis NPR1/NIM1 gene is a key regulator of systemic acquired resistance (SAR). Over‐expression of NPR1 leads to enhanced resistance in Arabidopsis. To investigate the role of NPR1 in monocots, we over‐expressed the Arabidopsis NPR1 in rice and challenged the transgenic plants with Xanthomonas oryzae pv. oryzae (Xoo), the rice bacterial blight pathogen. The transgenic plants displayed enhanced resistance to Xoo. RNA blot hybridization indicates that enhanced resistance requires expression of NPR1 mRNA above a threshold level in rice. To identify components mediating the resistance controlled by NPR1, we used NPR1 as bait in a yeast two‐hybrid screen. We isolated four cDNA clones encoding rice NPR1 interactors (named rTGA2.1, rTGA2.2, rTGA2.3 and rLG2) belonging to the bZIP family. rTGA2.1, rTGA2.2 and rTGA2.3 share 75, 76 and 78% identity with Arabidopsis TGA2, respectively. In contrast, rLG2 shares highest identity (81%) to the maize liguleless (LG2) gene product, which is involved in establishing the leaf blade–sheath boundary. The interaction of NPR1 with the rice bZIP proteins in yeast was impaired by the npr1‐1 and npr1‐2 mutations, but not by the nim1‐4 mutation. The NPR1–rTGA2.1 interaction was confirmed by an in vitro pull‐down experiment. In gel mobility shift assays, rTGA2.1 binds to the rice RCH10 promoter and to a cis‐element required sequence‐specifically for salicylic acid responsiveness. This is the first demonstration that the Arabidopsis NPR1 gene can enhance disease resistance in a monocot plant. These results also suggest that monocot and dicot plants share a conserved signal transduction pathway controlling NPR1‐mediated resistance.
Regulation of drought tolerance by gene manipulation of 9‐cis‐epoxycarotenoid dioxygenase, a key enzyme in abscisic acid biosynthesis in Arabidopsis
Authors: Iuchi Satoshi , Kobayashi Masatomo , Taji Teruaki , Naramoto Masaaki , Seki Motoaki , Kato Tomohiko , Tabata Satoshi , Kakubari Yoshitaka , Yamaguchi‐Shinozaki Kazuko , Shinozaki Kazuo 
Published: March 2003

SummaryAbscisic acid (ABA), a plant hormone, is involved in responses to environmental stresses such as drought and high salinity, and is required for stress tolerance. ABA is synthesized de novo in response to dehydration. 9‐cis‐epoxycarotenoid dioxygenase (NCED) is thought to be a key enzyme in ABA biosynthesis. Here we demonstrate that the expression of an NCED gene of Arabidopsis, AtNCED3, is induced by drought stress and controls the level of endogenous ABA under drought‐stressed conditions. Overexpression of AtNCED3 in transgenic Arabidopsis caused an increase in endogenous ABA level, and promoted transcription of drought‐ and ABA‐inducible genes. Plants overexpressing AtNCED3 showed a reduction in transpiration rate from leaves and an improvement in drought tolerance. By contrast, antisense suppression and disruption of AtNCED3 gave a drought‐sensitive phenotype. These results indicate that the expression of AtNCED3 plays a key role in ABA biosynthesis under drought‐stressed conditions in Arabidopsis. We improved drought tolerance by gene manipulation of AtNCED3 causing the accumulation of endogenous ABA.
A high‐throughput method for quantifying growth of phytopathogenic bacteria in Arabidopsis thaliana
Authors: Tornero Pablo , Dangl Jeffery L. 
Published: March 2003

SummaryMeasuring the growth of pathogenic bacteria in leaves is a mainstay of plant pathology studies. We have made significant improvements to standard methods that will not only increase the throughput but also reduce the space limitations. Additionally, the method described here is as accurate as the standard method. Briefly, we infected leaves by dipping whole seedlings of Arabidopsis into a bacterial solution containing a surfactant. After harvest, the seedlings were then simply shaken in buffer. The resulting bacterial solutions were diluted in microtitre plates and spotted onto agar plates. Colony‐forming units were then counted 40 h after plating. Therefore, we have eliminated most of the labour‐intensive steps involved in measuring the growth of bacteria in Arabidopsis, and describe a method that could be automated. The assay is sensitive enough to detect small differences between pathogens or ecotypes.
Identification and regulation of high light‐induced genes in Chlamydomonas reinhardtii
Authors: Im Chung Soon , Grossman Arthur R. 
Published: March 2003

SummaryWe have used restriction fragment differential display for isolating genes of the unicellular green alga Chlamydomonas reinhardtii that exhibit elevated expression on exposure of cells to high light. Some of the high light‐activated genes were also controlled by CO2 concentration. Genes requiring both elevated light and low CO2 levels for activation encoded both novel polypeptides and those that function in concentrating inorganic carbon (extracellular carbonic anhydrase, low CO2‐induced protein, ABC transporter of the MRP subfamily). All the genes in this category were shown to be under the control of Cia5, a protein that regulates the responses of C. reinhardtii to low‐CO2 conditions. Genes specifically activated by high light, even under high‐CO2 conditions, encoded a 30 kDa chloroplast membrane protein, a serine hydroxymethyltransferase, a nuclease, and two proteins of unknown function. Experiments using DCMU, an inhibitor of photosynthetic electron transport, and mutants devoid of either photosystem I or photosystem II activity, showed aberrant expression of all the genes regulated by both CO2 and high light, suggesting that redox plays a role in controlling their expression. In contrast, there was little effect of DCMU or lesions that block photosynthetic electron transport on the activity of genes that were specifically controlled by high light.
Antisense inhibition of protein phosphatase 2C accelerates cold acclimation in Arabidopsis thaliana
Authors: Tähtiharju Sari , Palva Tapio 
Published: March 2003

SummaryTwo related protein phosphatases 2C, ABI1 and AtPP2CA have been implicated as negative regulators of ABA signalling. In this study we characterized the role of AtPP2CA in cold acclimation. The pattern of expression of AtPP2CA and ABI1 was studied in different tissues and in response to abiotic stresses. The expression of both AtPP2CA and ABI1 was induced by low temperature, drought, high salt and ABA. The cold and drought‐induced expression of these genes was ABA‐dependent, but divergent in various ABA signalling mutants. In addition, the two PP2C genes exhibited differences in their tissue‐specific expression as well as in temporal induction in response to low temperature. To elucidate the function of AtPP2CA in cold acclimation further, the corresponding gene was silenced by antisense inhibition. Transgenic antisense plants exhibited clearly accelerated development of freezing tolerance. Both exposure to low temperature and application of ABA resulted in enhanced freezing tolerance in antisense plants. These plants displayed increased sensitivity to ABA both during development of frost tolerance and during seed germination, but not in their drought responses. Furthermore, the expression of cold‐and ABA‐induced genes was enhanced in transgenic antisense plants. Our results suggest that AtPP2CA is a negative regulator of ABA responses during cold acclimation.
Molecular analysis of the acetolactate synthase gene of Chlamydomonas reinhardtii and development of a genetically engineered gene as a dominant selectable marker for genetic transformation
Authors: Kovar Joy L. , Zhang Jun , Funke Roel P. , Weeks Donald P. 
Published: March 2003

SummaryGenomic and cDNA clones of the acetolactate synthase (ALS) gene of Chlamydomonas reinhardtii have been isolated from a mutant, c85–20 (Hartnett et al., 1987), that is resistant to high concentrations of sulfometuron methyl (SMM) and related sulfonylurea herbicides. Comparison of the ALS gene sequences from the wild‐type and the SMM resistant (SMMr) strains revealed two amino acid differences in the mature enzyme, a lysine to threonine change at position 257 (K257T) and a leucine to valine change at position 294 (L294V). Transformation of wild‐type C. reinhardtii with the mutant ALS gene produced no transformants with ability to grow in the presence of a minimum toxic concentration of SMM (3 µm). Substitution of the ALS promoter with the promoter of the C. reinhardtii Rubisco small subunit gene (RbcS2) permitted recovery of SMMr colonies. In vitro mutagenesis of the wild‐type ALS gene to produce various combinations of mutations (K257T, L294V and W580L) indicated that the K257T mutation was necessary and sufficient to confer the SMMr phenotype. Optimum transformation rates were obtained with two constructs (pJK7 and pRP‐ALS) in which all introns in the coding region were present. Rates of transformation with construct pJK7 were approximately 2.5 × 10−4 transformants/cell (i.e. one transformant for each of 4000 initial cells) using electroporation and 8.5 × 10−6 transformants/cell using the glass bead vortexing method. These results suggest that pJK7 and pRP‐ALS can serve as important additional dominant selectable markers for the genetic transformation of C. reinhardtii.
The water permeability of Arabidopsis plasma membrane is regulated by divalent cations and pH
Authors: Gerbeau Patricia , Amodeo Gabriela , Henzler Tobias , Santoni Véronique , Ripoche Pierre , Maurel Christophe 
Published: March 2003

SummaryMechanisms that regulate water channels in the plant plasma membrane (PM) were investigated in Arabidopsis suspension cells. Cell hydraulic conductivity was measured with a cell pressure probe and was reduced 4‐fold as compared to control values when calcium was added in the pipette and in bathing solution. To assess the significance of these effects in vitro, PM vesicles were isolated by aqueous two‐phase partitioning and their water transport properties were characterized by stopped‐flow spectrophotometry. Membrane vesicles isolated in standard conditions exhibited reduced water permeability (Pf) together with a lack of active water channels. In contrast, when prepared in the presence of chelators of divalent cations, PM vesicles showed a 2.3‐fold higher Pf and active water channels. Furthermore, equilibration of purified PM vesicles with divalent cations reduced their Pf and water channel activity down to the basal level of membranes isolated in standard conditions. Ca2+ was the most efficient with a half‐inhibition of Pf at 50–100 µm free Ca2+. Water transport in purified PM vesicles was also reversibly blocked by H+, with a half‐inhibition of Pf at pH 7.2–7.5. Thus, both Ca2+ and H+ contribute to a membrane‐delimited switch from active to inactive water channels that may allow coupling of water transport to cell signalling and metabolism.
A novelin vitrosystem for simultaneous import of precursor proteins into mitochondria and chloroplasts
Authors: Rudhe Charlotta , Chew Orinda , Whelan James , Glaser Elzbieta 
Published: March 2003

SummaryMost chloroplast and mitochondrial precursor proteins are targeted specifically to either chloroplasts or mitochondria. However, there is a group of proteins that are dual targeted to both organelles. We have developed a novelin vitrosystem for simultaneous import of precursor proteins into mitochondria and chloroplasts (dual import system). The mitochondrial precursor of alternative oxidase, AOX was specifically targeted only to mitochondria. The chloroplastic precursor of small subunit of pea ribulose bisphosphate carboxylase/oxygenase, Rubisco, was mistargeted to pea mitochondria in a single import system, but was imported only into chloroplasts in the dual import system. The dual targeted glutathione reductase GR precursor was targeted to both mitochondria and chloroplasts in both systems. The GR pre‐sequence could support import of the mature Rubisco protein into mitochondria and chloroplasts in the single import system but only into chloroplasts in the dual import system. Although the GR pre‐sequence could support import of the mature portion of the mitochondrial FAd subunit of the ATP synthase into mitochondria and chloroplasts, mature AOX protein was only imported into mitochondria under the control of the GR pre‐sequence in both systems. These results show that the novel dual import system is superior to the single import system as it abolishes mistargeting of chloroplast precursors into pea mitochondria observed in a single organelle import system. The results clearly show that although the GR pre‐sequence has dual targeting ability, this ability is dependent on the nature of the mature protein.