bluuebunny/crossref_metadata_2025 huggingface dataset:
Exceptional chemical and thermal stability of zeolitic imidazolate frameworks
Authors: Park Kyo Sung , Ni Zheng , Côté Adrien P. , Choi Jae Yong , Huang Rudan , Uribe-Romo Fernando J. , Chae Hee K. , O’Keeffe Michael , Yaghi Omar M.
Published: June 2006

Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m
2
/g), high thermal stability (up to 550°C), and remarkable chemical resistance to boiling alkaline water and organic solvents.
A burst of auxilin recruitment determines the onset of clathrin-coated vesicle uncoating
Authors: Massol Ramiro H. , Boll Werner , Griffin April M. , Kirchhausen Tomas
Published: June 2006

Clathrin-coated pits assemble on a membrane and pinch off as coated vesicles. The released vesicles then rapidly lose their clathrin coats in a process mediated by the ATPase Hsc70, recruited by auxilin, a J-domain-containing cofactor. How is the uncoating process regulated? We find that during coat assembly small and variable amounts of auxilin are recruited transiently but that a much larger burst of association occurs after the peak of dynamin signal, during the transition between membrane constriction and vesicle budding. We show that the auxilin burst depends on domains of the protein likely to interact with lipid head groups. We conclude that the timing of auxilin recruitment determines the onset of uncoating. We propose that, when a diffusion barrier is established at the constricting neck of a fully formed coated pit and immediately after vesicle budding, accumulation of a specific lipid can recruit sufficient auxilin molecules to trigger uncoating.
Nonhepatic origin of notothenioid antifreeze reveals pancreatic synthesis as common mechanism in polar fish freezing avoidance
Authors: Cheng Chi-Hing C. , Cziko Paul A. , Evans Clive W.
Published: June 2006

Phylogenetically diverse polar and subpolar marine teleost fishes have evolved antifreeze proteins (AFPs) or antifreeze glycoproteins (AFGPs) to avoid inoculative freezing by internalized ice. For over three decades since the first fish antifreeze (AF) protein was discovered, many studies of teleost freezing avoidance showed hepatic AF synthesis and distribution within the circulation as pivotal in preventing the blood, and therefore the fish, from freezing. We have uncovered an important twist to this long-held paradigm: the complete absence of liver synthesis of AFGPs in any life stage of the Antarctic notothenioids, indicating that the liver plays no role in the freezing avoidance in these fishes. Instead, we found the exocrine pancreas to be the major site of AFGP synthesis and secretion in all life stages, and that pancreatic AFGPs enter the intestinal lumen via the pancreatic duct to prevent ingested ice from nucleating the hyposmotic intestinal fluids. AFGPs appear to remain undegraded in the intestinal milieu, and the composition and relative abundance of intestinal AFGP isoforms are nearly identical to serum AFGPs. Thus, the reabsorption of intact pancreas-derived intestinal AFGPs, and not the liver, is the likely source of circulatory AFGPs in notothenioid fishes. We examined diverse northern fish taxa and Antarctic eelpouts with hepatic synthesis of bloodborne AF and found that they also express secreted pancreatic AF of their respective types. The evolutionary convergence of this functional physiology underscores the hitherto largely unrecognized importance of intestinal freezing prevention in polar teleost freezing avoidance, especially in the chronically icy Antarctic waters.
Aphid alarm pheromone produced by transgenic plants affects aphid and parasitoid behavior
Authors: Beale Michael H. , Birkett Michael A. , Bruce Toby J. A. , Chamberlain Keith , Field Linda M. , Huttly Alison K. , Martin Janet L. , Parker Rachel , Phillips Andrew L. , Pickett John A. , Prosser Ian M. , Shewry Peter R. , Smart Lesley E. , Wadhams Lester J. , Woodcock Christine M. , Zhang Yuhua
Published: June 2006

The alarm pheromone for many species of aphids, which causes dispersion in response to attack by predators or parasitoids, consists of the sesquiterpene (E)-β-farnesene (Eβf). We used high levels of expression inArabidopsis thalianaplants of anEβf synthase gene cloned fromMentha×piperitato cause emission of pureEβf. These plants elicited potent effects on behavior of the aphidMyzus persicae(alarm and repellent responses) and its parasitoidDiaeretiella rapae(an arrestant response). Here, we report the transformation of a plant to produce an insect pheromone and demonstrate that the resulting emission affects behavioral responses at two trophic levels.
TNF-α inhibits asbestos-induced cytotoxicity via a NF-κB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis
Authors: Yang Haining , Bocchetta Maurizio , Kroczynska Barbara , Elmishad Amira G. , Chen Yuanbin , Liu Zemin , Bubici Concetta , Mossman Brooke T. , Pass Harvey I. , Testa Joseph R. , Franzoso Guido , Carbone Michele
Published: June 2006

Asbestos is the main cause of human malignant mesothelioma (MM).In vivo, macrophages phagocytize asbestos and, in response, release TNF-α and other cytokines that contribute to carcinogenesis through unknown mechanisms.In vitro, asbestos does not induce transformation of primary human mesothelial cells (HM); instead, asbestos is very cytotoxic to HM, causing extensive cell death. This finding raised an apparent paradox: How can asbestos cause MM if HM exposed to asbestos die? We found that asbestos induced the secretion of TNF-α and the expression of TNF-α receptor I in HM. Treatment of HM with TNF-α significantly reduced asbestos cytotoxicity. Through numerous technical approaches, including chemical inhibitors and small interfering RNA strategies, we demonstrate that, in HM, TNF-α activates NF-κB and that NF-κB activation leads to HM survival and resistance to the cytotoxic effects of asbestos. Our data show a critical role for TNF-α and NF-κB signaling in mediating HM responses to asbestos. TNF-α signaling through NF-κB-dependent mechanisms increases the percent of HM that survives asbestos exposure, thus increasing the pool of asbestos-damaged HM that are susceptible to malignant transformation. Cytogenetics supported this hypothesis, showing only rare, aberrant metaphases in HM exposed to asbestos and an increased mitotic rate with fewer irregular metaphases in HM exposed to both TNF-α and asbestos. Our findings provide a mechanistic rationale for the paradoxical inability of asbestos to transform HMin vitro, elucidate and underscore the role of TNF-α in asbestos pathogenesis in humans, and identify potential molecular targets for anti-MM prevention and therapy.
Mating-responsive genes in reproductive tissues of femaleDrosophila melanogaster
Authors: Mack Paul D. , Kapelnikov Anat , Heifetz Yael , Bender Michael
Published: June 2006

Male-derived accessory gland proteins that are transferred to females during mating have profound effects on female reproductive physiology including increased ovulation, mating inhibition, and effects on sperm utilization and storage. The extreme rates of evolution seen in accessory gland proteins may be driven by sperm competition and sexual conflict, processes that may ultimately drive complex interactions between female- and male-derived molecules and sperm. However, little is known of how gene expression in female reproductive tissues changes in response to the presence of male molecules and sperm. To characterize this response, we conducted parallel genomic and proteomic analyses of gene expression in the reproductive tract of 3-day-old unmated and mated femaleDrosophila melanogaster. Using DNA microarrays, we identified 539 transcripts that are differentially expressed in unmated vs. mated females and revealed a striking peak in differential expression at 6 h postmating and a marked shift from primarily down-regulated to primarily up-regulated transcripts within 3 h after mating. Combining two-dimensional gel electrophoresis and liquid chromatography mass spectrometry analyses, we identified 84 differentially expressed proteins at 3 h postmating, including proteins that appeared to undergo posttranslational modification. Together, our observations define transcriptional and translational response to mating within the female reproductive tract and suggest a bimodal model of postmating gene expression initially correlated with mating and the final stages of female reproductive tract maturation and later with the declining presence of male reproductive molecules and with sperm maintenance and utilization.
Aspm specifically maintains symmetric proliferative divisions of neuroepithelial cells
Authors: Fish Jennifer L. , Kosodo Yoichi , Enard Wolfgang , Pääbo Svante , Huttner Wieland B.
Published: June 2006

The ASPM (abnormal spindle-like microcephaly-associated) protein has previously been implicated in the determination of human cerebral cortical size, but the cell biological basis of this regulation has not been studied. Here we investigate the role of Aspm in mouse embryonic neuroepithelial (NE) cells, the primary stem and progenitor cells of the mammalian brain. Aspm was found to be concentrated at mitotic spindle poles of NE cells and to be down-regulated with their switch from proliferative to neurogenic divisions. Upon RNA interference in telencephalic NE cells,
Aspm
mRNA is reduced, mitotic spindle poles lack Aspm protein, and the cleavage plane of NE cells is less frequently oriented perpendicular to the ventricular surface of the neuroepithelium. The alteration in the cleavage plane orientation of NE cells increases the probability that these highly polarized cells undergo asymmetric division, i.e., that apical plasma membrane is inherited by only one of the daughter cells. Concomitant with the resulting increase in abventricular cells in the ventricular zone, a larger proportion of NE cell progeny is found in the neuronal layer, implying a reduction in the number of NE progenitor cells upon Aspm knock-down relative to control. Our results demonstrate that Aspm is crucial for maintaining a cleavage plane orientation that allows symmetric, proliferative divisions of NE cells during brain development. These data provide a cell biological explanation of the primary microcephaly observed in humans with mutations in
ASPM
, which also has implications for the evolution of mammalian brains.
Os8N3
is a host disease-susceptibility gene for bacterial blight of rice
Authors: Yang Bing , Sugio Akiko , White Frank F.
Published: June 2006

Many bacterial diseases of plants depend on the interaction of type III effector genes of the pathogen and disease-susceptibility genes of the host. The host susceptibility genes are largely unknown. Here, we show that expression of the rice gene
Os8N3
, a member of the
MtN3
gene family from plants and animals, is elevated upon infection by
Xanthomonas oryzae
pv.
oryzae
strain PXO99
A
and depends on the type III effector gene
pthXo1
.
Os8N3
resides near
xa13
, and PXO99
A
failed to induce
Os8N3
in rice lines with
xa13
. Silencing of
Os8N3
by inhibitory RNA produced plants that were resistant to infection by strain PXO99
A
yet remained susceptible to other strains of the pathogen. The effector gene
avrXa7
from strain PXO86 enabled PXO99
A
compatibility on either
xa13
- or
Os8N3
-silenced plants. The findings indicate that
Os8N3
is a host susceptibility gene for bacterial blight targeted by the type III effector PthXo1. The results support the hypothesis that
X. oryzae
pv.
oryzae
commandeers the regulation of otherwise developmentally regulated host genes to induce a state of disease susceptibility. Furthermore, the results support a model in which the pathogen induces disease susceptibility in a gene-for-gene manner.
Origins and evolution of the
recA
/
RAD51
gene family: Evidence for ancient gene duplication and endosymbiotic gene transfer
Authors: Lin Zhenguo , Kong Hongzhi , Nei Masatoshi , Ma Hong
Published: June 2006

The bacterial
recA
gene and its eukaryotic homolog
RAD51
are important for DNA repair, homologous recombination, and genome stability. Members of the
recA/RAD51
family have functions that have differentiated during evolution. However, the evolutionary history and relationships of these members remains unclear. Homolog searches in prokaryotes and eukaryotes indicated that most eubacteria contain only one
recA
. However, many archaeal species have two
recA/RAD51
homologs (
RADA
and
RADB
), and eukaryotes possess multiple members (
RAD51
,
RAD51B
,
RAD51C
,
RAD51D
,
DMC1
,
XRCC2
,
XRCC3
, and
recA
). Phylogenetic analyses indicated that the
recA/RAD51
family can be divided into three subfamilies: (
i
)
RADα
, with highly conserved functions; (
ii
)
RADβ
, with relatively divergent functions; and (
iii
)
recA
, functioning in eubacteria and eukaryotic organelles. The
RADα
and
RAD
β subfamilies each contain archaeal and eukaryotic members, suggesting that a gene duplication occurred before the archaea/eukaryote split. In the
RAD
α subfamily, eukaryotic
RAD51
and
DMC1
genes formed two separate monophyletic groups when archaeal
RADA
genes were used as an outgroup. This result suggests that another duplication event occurred in the early stage of eukaryotic evolution, producing the
DMC1
clade with meiosis-specific genes. The
RAD
β subfamily has a basal archaeal clade and five eukaryotic clades, suggesting that four eukaryotic duplication events occurred before animals and plants diverged. The eukaryotic
recA
genes were detected in plants and protists and showed strikingly high levels of sequence similarity to
recA
genes from proteobacteria or cyanobacteria. These results suggest that endosymbiotic transfer of
recA
genes occurred from mitochondria and chloroplasts to nuclear genomes of ancestral eukaryotes.
Pyrogenic Reactions and Hemorrhage Associated With Intrinsic Exposure to Endotoxin-Contaminated Intravenous Solutions
Authors: Daufenbach Luciane Zappelini , Alves Waneska A. , de Azevedo Jaime B. , Arduino Matthew J. , Forster Terri S. , Carmo Eduardo H. , Hatch Douglas L.
Published: June 2006

Objective.

An epidemiological investigation was conducted to determine risk factors for adverse reactions among patients in hospitals and the possibility of extrinsic or intrinsic contamination of intravenous solutions.

Design.

A retrospective cohort study was conducted to identify solutions associated with adverse reactions. Implicated lots were cultured for bacteria, and endotoxin concentrations were measured.

Setting.

Five hospitals in the state of Pernambuco, Brazil, were investigated from February through March 2002.

Patients.

Surgical inpatients or outpatients receiving intravenous solutions during the study period.

Results.

Of 355 surgical patients or outpatients treated at hospitals, 28 (8%) developed illness within a mean of 2.5 hours after exposure to intravenous solutions implicated in adverse reactions; 5 (17.9%) of the case patients died. Laboratory testing of bottles from the lots of Ringer's lactate solution implicated in deaths demonstrated a high mean endotoxin concentration of 88.3 endotoxin units (EU)/mL (range, 9.7-298.0 EU/mL), compared with the permitted limit in Brazil of <0.5 EU/mL. Testing of metronidazole implicated in adverse reactions at another hospital and produced by the same company that manufactured the lots Ringer's lactate solution also showed high endotoxin concentrations (mean level, 8.3 EU/mL [range, 5.0-58.3 EU/mL]). The outbreak was controlled after a national recall of the implicated brand of intravenous solutions.

Conclusions.

Case patient status was associated with use of Ringer's lactate solution and metronidazole from large bottles, both of which were produced by the same company. High endotoxin concentrations were demonstrated in unopened bottles of implicated products, which is consistent with intrinsic contamination. The high mortality rate may have been compounded by the fact that clinicians administered additional volumes of contaminated 0.9% isotonic sodium chloride solution in response to hypotension or bleeding to some surgical patients. No additional case patients were identified after a national recall of products, inspection, closure of the implicated company's manufacturing facility, and establishment of random quality-control testing of intravenous solutions.
ONE WORLD, ONE CURRENCY: EXPLORING THE ISSUES
Authors: STARR MARTHA A.
Published: June 2006

Along with globalization of trade and finance has come a certain globalization of money. Some countries have adopted monetary unions and currency boards; others increasingly use international currencies in place of national monies. This article explores the idea of a global money—framed here as a voluntary, representative arrangement based on accepted principles for optimal conduct monetary policy. It argues that if the current pace of economic and financial integration continues, a global money may emerge that is better adapted to internationalization of production and exchange—although such a change may be a long time in coming. (JEL F330, F360, E420)
The last mile: earthquake risk mitigation assistance in developing countries
Authors: Shah Haresh C
Published: June 2006

Over the past few decades, we have seen many joint programmes between developed countries and developing countries to help the latter in managing their earthquake risks. These programmes span the whole spectrum of disciplines from seismology and geology to engineering, social science and economics. Many of these programmes have been effective in raising awareness, in urging governments to work towards risk reduction and in spawning an ‘industry’ of disaster management in many of the developing countries. However, even as these efforts proceed, we have seen death and destruction due to earthquake after earthquake in developing countries, strongly suggesting that the problems for which those assistance programmes were developed are not so effective. Therefore, it is natural to ask why this is happening. Are the assistance programmes reaching the right people? Maybe we are reaching the right people and doing the right type of things in these countries, but we have not allowed enough time for our actions to take effect. Maybe we are reaching the right people and doing the right actions for most of the miles we need to cover in helping communities mitigate their earthquake risks. However, the issue could be whether we are reaching people who represent the ‘last mile’ on this pathway. Here, I explore whether the work that many organizations and countries have done towards earthquake risk reduction over the past few decades in developing countries is appropriate or not. Why do we keep seeing the catastrophes of Sumatra, Chi Chi, Bhuj, Turkey, Algeria and on and on? I will articulate what I think is the problem. My contribution is intended to generate discussions, self-analysis of our approaches, what we are doing right and what we are not doing right. Hopefully such discussions will result in a better connection between the last mile and programmes around the world which are working towards earthquake risk mitigation.
L1 Division and Differentiation Patterns Influence Shoot Apical Meristem Maintenance
Authors: Kessler Sharon , Townsley Brad , Sinha Neelima
Published: June 2006

Plant development requires regulation of both cell division and differentiation. The class 1 KNOTTED1-like homeobox (KNOX) genes such as knotted1 (kn1) in maize (Zea mays) and SHOOTMERISTEMLESS in Arabidopsis (Arabidopsis thaliana) play a role in maintaining shoot apical meristem indeterminacy, and their misexpression is sufficient to induce cell division and meristem formation. KNOX overexpression experiments have shown that these genes interact with the cytokinin, auxin, and gibberellin pathways. The L1 layer has been shown to be necessary for the maintenance of indeterminacy in the underlying meristem layers. This work explores the possibility that the L1 affects meristem function by disrupting hormone transport pathways. The semidominant Extra cell layers1 (Xcl1) mutation in maize leads to the production of multiple epidermal layers by overproduction of a normal gene product. Meristem size is reduced in mutant plants and more cells are incorporated into the incipient leaf primordium. Thus, Xcl1 may provide a link between L1 division patterns, hormonal pathways, and meristem maintenance. We used double mutants between Xcl1 and dominant KNOX mutants and showed that Xcl1 suppresses the Kn1 phenotype but has a synergistic interaction with gnarley1 and rough sheath1, possibly correlated with changes in gibberellin and auxin signaling. In addition, double mutants between Xcl1 and crinkly4 had defects in shoot meristem maintenance. Thus, proper L1 development is essential for meristem function, and XCL1 may act to coordinate hormonal effects with KNOX gene function at the shoot apex.
Imaging of Dynamic Secretory Vesicles in Living Pollen Tubes of Picea meyeri Using Evanescent Wave Microscopy
Authors: Wang Xiaohua , Teng Yan , Wang Qinli , Li Xiaojuan , Sheng Xianyong , Zheng Maozhong , Šamaj Jozef , Baluška František , Lin Jinxing
Published: June 2006

Evanescent wave excitation was used to visualize individual, FM4-64-labeled secretory vesicles in an optical slice proximal to the plasma membrane of Picea meyeri pollen tubes. A standard upright microscope was modified to accommodate the optics used to direct a laser beam at a variable angle. Under evanescent wave microscopy or total internal reflection fluorescence microscopy, fluorophores localized near the surface were excited with evanescent waves, which decay exponentially with distance from the interface. Evanescent waves with penetration depths of 60 to 400 nm were generated by varying the angle of incidence of the laser beam. Kinetic analysis of vesicle trafficking was made through an approximately 300-nm optical section beneath the plasma membrane using time-lapse evanescent wave imaging of individual fluorescently labeled vesicles. Two-dimensional trajectories of individual vesicles were obtained from the resulting time-resolved image stacks and were used to characterize the vesicles in terms of their average fluorescence and mobility, expressed here as the two-dimensional diffusion coefficient D2. The velocity and direction of vesicle motions, frame-to-frame displacement, and vesicle trajectories were also calculated. Analysis of individual vesicles revealed for the first time, to our knowledge, that two types of motion are present, and that vesicles in living pollen tubes exhibit complicated behaviors and oscillations that differ from the simple Brownian motion reported in previous investigations. Furthermore, disruption of the actin cytoskeleton had a much more pronounced effect on vesicle mobility than did disruption of the microtubules, suggesting that actin cytoskeleton plays a primary role in vesicle mobility.
Bestatin, an Inhibitor of Aminopeptidases, Provides a Chemical Genetics Approach to Dissect Jasmonate Signaling in Arabidopsis
Authors: Zheng Wenguang , Zhai Qingzhe , Sun Jiaqiang , Li Chang-Bao , Zhang Lei , Li Hongmei , Zhang Xiaoli , Li Shuyu , Xu Yingxiu , Jiang Hongling , Wu Xiaoyan , Li Chuanyou
Published: June 2006

Bestatin, a potent inhibitor of some aminopeptidases, was shown previously to be a powerful inducer of wound-response genes in tomato (Lycopersicon esculentum). Here, we present several lines of evidence showing that bestatin specifically activates jasmonic acid (JA) signaling in plants. First, bestatin specifically activates the expression of JA-inducible genes in tomato and Arabidopsis (Arabidopsis thaliana). Second, the induction of JA-responsive genes by bestatin requires the COI1-dependent JA-signaling pathway, but does not depend strictly on JA biosynthesis. Third, microarray analysis using Arabidopsis whole-genome chip demonstrates that the gene expression profile of bestatin-treated plants is similar to that of JA-treated plants. Fourth, bestatin promotes a series of JA-related developmental phenotypes. Taken together, the unique action mode of bestatin in regulating JA-signaled processes leads us to the hypothesis that bestatin exerts its effects through the modulation of some key regulators in JA signaling. We have employed bestatin as an experimental tool to dissect JA signaling through a chemical genetic screening, which yielded a collection of Arabidopsis bestatin-resistant (ber) mutants that are insensitive to the inhibitory effects of bestatin on root elongation. Further characterization efforts demonstrate that some ber mutants are defective in various JA-induced responses, which allowed us to classify the ber mutants into three phenotypic groups: JA-insensitive ber mutants, JA-hypersensitive ber mutants, and mutants insensitive to bestatin but showing normal response to JA. Genetic and phenotypic analyses of the ber mutants with altered JA responses indicate that we have identified several novel loci involved in JA signaling.
Activation of Ntf4, a Tobacco Mitogen-Activated Protein Kinase, during Plant Defense Response and Its Involvement in Hypersensitive Response-Like Cell Death
Authors: Ren Dongtao , Yang Kwang-Yeol , Li Guo-Jing , Liu Yidong , Zhang Shuqun
Published: June 2006

Mitogen-activated protein kinase (MAPK) cascades are important signaling modules in eukaryotic cells. They function downstream of sensors/receptors and regulate cellular responses to external and endogenous stimuli. Recent studies demonstrated that SIPK and WIPK, two tobacco (Nicotiana spp.) MAPKs, are involved in signaling plant defense responses to various pathogens. Ntf4, another tobacco MAPK that shares 93.6% and 72.3% identity with SIPK and WIPK, respectively, was reported to be developmentally regulated and function in pollen germination. We found that Ntf4 is also expressed in leaves and suspension-cultured cells. Genomic analysis excluded the possibility that Ntf4 and SIPK are orthologs from the two parental lines of the amphidiploid common tobacco. In vitro and in vivo phosphorylation and activation assays revealed that Ntf4 shares the same upstream MAPK kinase, NtMEK2, with SIPK and WIPK. Similar to SIPK and WIPK, Ntf4 is also stress responsive and can be activated by cryptogein, a proteinaceous elicitin from oomycetic pathogen Phytophthora cryptogea. Tobacco recognition of cryptogein induces rapid hypersensitive response (HR) cell death in tobacco. Transgenic Ntf4 plants with elevated levels of Ntf4 protein showed accelerated HR cell death when treated with cryptogein. In addition, conditional overexpression of Ntf4, which results in high cellular Ntf4 activity, is sufficient to induce HR-like cell death. Based on these results, we concluded that Ntf4 is multifunctional. In addition to its role in pollen germination, Ntf4 is also a component downstream of NtMEK2 in the MAPK cascade that regulates pathogen-induced HR cell death in tobacco.
Effects of Endogenous Salicylic Acid on Nodulation in the Model Legumes Lotus japonicus and Medicago truncatula
Authors: Stacey Gary , McAlvin Crystal Bickley , Kim Sung-Yong , Olivares José , Soto María José
Published: June 2006

The exogenous addition of salicylic acid (SA) was previously shown to inhibit indeterminate but not determinate-type nodulation. We sought to extend these results by modulating endogenous levels of SA through the transgenic expression of salicylate hydroxylase (NahG) in both stably transformed Lotus japonicus and composite Medicago truncatula plants. NahG expression in L. japonicus resulted in a marked reduction of SA levels. This reduction correlated with an increase in the number of infections and mean nodule number when compared to controls. However, a complicating factor was that NahG-expressing plants had greater root growth. Spot inoculations of NahG-expressing L. japonicus plants confirmed increased nodulation in these plants. Consistent with the reported inhibitory effects of exogenous SA on indeterminate-type nodulation, NahG expression in M. truncatula plants led to enhanced nodulation and infection. These data point to an important role for SA-mediated plant defense pathways in controlling nodule formation on both determinate and indeterminate nodule-forming hosts.
Enhancement of Abscisic Acid Sensitivity and Reduction of Water Consumption in Arabidopsis by Combined Inactivation of the Protein Phosphatases Type 2C ABI1 and HAB1
Authors: Saez Angela , Robert Nadia , Maktabi Mohammad H. , Schroeder Julian I. , Serrano Ramón , Rodriguez Pedro L.
Published: June 2006

Abscisic acid (ABA) plays a key role in plant responses to abiotic stress, particularly drought stress. A wide number of ABA-hypersensitive mutants is known, however, only a few of them resist/avoid drought stress. In this work we have generated ABA-hypersensitive drought-avoidant mutants by simultaneous inactivation of two negative regulators of ABA signaling, i.e. the protein phosphatases type 2C (PP2Cs) ABA-INSENSITIVE1 (ABI1) and HYPERSENSITIVE TO ABA1 (HAB1). Two new recessive loss-of-function alleles of ABI1, abi1-2 and abi1-3, were identified in an Arabidopsis (Arabidopsis thaliana) T-DNA collection. These mutants showed enhanced responses to ABA both in seed and vegetative tissues, but only a limited effect on plant drought avoidance. In contrast, generation of double hab1-1 abi1-2 and hab1-1 abi1-3 mutants strongly increased plant responsiveness to ABA. Thus, both hab1-1 abi1-2 and hab1-1 abi1-3 were particularly sensitive to ABA-mediated inhibition of seed germination. Additionally, vegetative responses to ABA were reinforced in the double mutants, which showed a strong hypersensitivity to ABA in growth assays, stomatal closure, and induction of ABA-responsive genes. Transpirational water loss under drought conditions was noticeably reduced in the double mutants as compared to single parental mutants, which resulted in reduced water consumption of whole plants. Taken together, these results reveal cooperative negative regulation of ABA signaling by ABI1 and HAB1 and suggest that fine tuning of ABA signaling can be attained through combined action of PP2Cs. Finally, these results suggest that combined inactivation of specific PP2Cs involved in ABA signaling could provide an approach for improving crop performance under drought stress conditions.
Cytosolic Triacylglycerol Biosynthetic Pathway in Oilseeds. Molecular Cloning and Expression of Peanut Cytosolic Diacylglycerol Acyltransferase
Authors: Saha Saikat , Enugutti Balaji , Rajakumari Sona , Rajasekharan Ram
Published: June 2006

Triacylglycerols (TAGs) are the most important storage form of energy for eukaryotic cells. TAG biosynthetic activity was identified in the cytosolic fraction of developing peanut (Arachis hypogaea) cotyledons. This activity was NaF insensitive and acyl-coenzyme A (CoA) dependent. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the final step in TAG biosynthesis that acylates diacylglycerol to TAG. Soluble DGAT was identified from immature peanuts and purified by conventional column chromatographic procedures. The enzyme has a molecular mass of 41 ± 1.0 kD. Based on the partial peptide sequence, a degenerate probe was used to obtain the full-length cDNA. The isolated gene shared less than 10% identity with the previously identified DGAT1 and 2 families, but has 13% identity with the bacterial bifunctional wax ester/DGAT. To differentiate the unrelated families, we designate the peanut gene as AhDGAT. Expression of peanut cDNA in Escherichia coli resulted in the formation of labeled TAG and wax ester from [14C]acetate. The recombinant E. coli showed high levels of DGAT activity but no wax ester synthase activity. TAGs were localized in transformed cells with Nile blue A and oil red O staining. The recombinant and native DGAT was specific for 1,2-diacylglycerol and did not utilize hexadecanol, glycerol-3-phosphate, monoacylglycerol, lysophosphatidic acid, and lysophosphatidylcholine. Oleoyl-CoA was the preferred acyl donor as compared to palmitoyl- and stearoyl-CoAs. These data suggest that the cytosol is one of the sites for TAG biosynthesis in oilseeds. The identified pathway may present opportunities of bioengineering oil-yielding plants for increased oil production.
Iron Deficiency in Cyanobacteria Causes Monomerization of Photosystem I Trimers and Reduces the Capacity for State Transitions and the Effective Absorption Cross Section of Photosystem I in Vivo
Authors: Ivanov Alexander G. , Krol Marianna , Sveshnikov Dmitry , Selstam Eva , Sandström Stefan , Koochek Maryam , Park Youn-Il , Vasil'ev Sergej , Bruce Doug , Öquist Gunnar , Huner Norman P.A.
Published: June 2006

The induction of the isiA (CP43′) protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43′ proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43′-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43′ does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43′ as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.
Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels
Authors: Shabala Sergey , Demidchik Vadim , Shabala Lana , Cuin Tracey A. , Smith Susan J. , Miller Anthony J. , Davies Julia M. , Newman Ian A.
Published: June 2006

Calcium can ameliorate Na+ toxicity in plants by decreasing Na+ influx through nonselective cation channels. Here, we show that elevated external [Ca2+] also inhibits Na+-induced K+ efflux through outwardly directed, K+-permeable channels. Noninvasive ion flux measuring and patch-clamp techniques were used to characterize K+ fluxes from Arabidopsis (Arabidopsis thaliana) root mature epidermis and leaf mesophyll under various Ca2+ to Na+ ratios. NaCl-induced K+ efflux was not related to the osmotic component of the salt stress, was inhibited by the K+ channel blocker TEA+, was not mediated by inwardly directed K+ channels (tested in the akt1 mutant), and resulted in a significant decrease in cytosolic K+ content. NaCl-induced K+ efflux was partially inhibited by 1 mm Ca2+ and fully prevented by 10 mm Ca2+. This ameliorative effect was at least partially attributed to a less dramatic NaCl-induced membrane depolarization under high Ca2+ conditions. Patch-clamp experiments (whole-cell mode) have demonstrated that two populations of Ca2+-sensitive K+ efflux channels exist in protoplasts isolated from the mature epidermis of Arabidopsis root and leaf mesophyll cells. The instantaneously activating K+ efflux channels showed weak voltage dependence and insensitivity to external and internal Na+. Another population of K+ efflux channels was slowly activating, steeply rectifying, and highly sensitive to Na+. K+ efflux channels in roots and leaves showed different Ca2+ and Na+ sensitivities, suggesting that these organs may employ different strategies to withstand salinity. Our results suggest an additional mechanism of Ca2+ action on salt toxicity in plants: the amelioration of K+ loss from the cell by regulating (both directly and indirectly) K+ efflux channels.
Natural Variation for Carbohydrate Content in Arabidopsis. Interaction with Complex Traits Dissected by Quantitative Genetics
Authors: Calenge Fanny , Saliba-Colombani Véra , Mahieu Stéphanie , Loudet Olivier , Daniel-Vedele Françoise , Krapp Anne
Published: June 2006

Besides being a metabolic fuel, carbohydrates play important roles in plant growth and development, in stress responses, and as signal molecules. We exploited natural variation in Arabidopsis (Arabidopsis thaliana) to decipher the genetic architecture determining carbohydrate content. A quantitative trait locus (QTL) approach in the Bay-0 × Shahdara progeny grown in two contrasting nitrogen environments led to the identification of 39 QTLs for starch, glucose, fructose, and sucrose contents representing at least 14 distinct polymorphic loci. A major QTL for fructose content (FR3.4) and a QTL for starch content (ST3.4) were confirmed in heterogeneous inbred families. Several genes associated with carbon (C) metabolism colocalize with the identified QTL. QTLs for senescence-related traits, and for flowering time, water status, and nitrogen-related traits, previously detected with the same genetic material, colocalize with C-related QTLs. These colocalizations reflect the complex interactions of C metabolism with other physiological processes. QTL fine-mapping and cloning could thus lead soon to the identification of genes potentially involved in the control of different connected physiological processes.
Synergism between RPBF Dof and RISBZ1 bZIP Activators in the Regulation of Rice Seed Expression Genes
Authors: Yamamoto Masayuki P. , Onodera Yasuyuki , Touno Satoru M. , Takaiwa Fumio
Published: June 2006

The Dof (DNA binding with one finger) transcriptional activator rice (Oryza sativa) prolamin box binding factor (RPBF), which is involved in gene regulation of rice seed storage proteins, has been isolated from rice cDNA expressed sequence tag clones containing the conserved Dof. RPBF is found as a single gene per haploid genome. Comparison of RPBF genomic and cDNA sequences revealed that the genomic copy is interrupted by one long intron of 1,892 bp in the 5′ noncoding region. We demonstrated by transient expression in rice callus protoplasts that the isolated RPBF trans-activated several storage protein genes via an AAAG target sequence located within their promoters, and with methylation interference experiments the additional AAAG-like sequences in promoters of genes expressed in maturing seeds were recognized by the RPBF protein. Binding was sequence specific, since mutation of the AAAG motif or its derivatives decreased both binding and trans-activation by RPBF. Synergism between RPBF and RISBZ1 recognizing the GCN4 motif [TGA(G/C)TCA] was observed in the expression of many storage protein genes. Overexpression of both transcription factors gave rise to much higher levels of expression than the sum of individual activities elicited by either RPBF or RISBZ1 alone. Furthermore, mutation of recognition sites suppressed reciprocal trans-activation ability, indicating that there are mutual interactions between RISBZ1 and RPBF. The RPBF gene is predominantly expressed in maturing endosperm and coordinately expressed with seed storage protein genes, and is involved in the quantitative regulation of genes expressed in the endosperm in cooperation with RISBZ1.
RCN1-Regulated Phosphatase Activity and EIN2 Modulate Hypocotyl Gravitropism by a Mechanism That Does Not Require Ethylene Signaling
Authors: Muday Gloria K. , Brady Shari R. , Argueso Cristiana , Deruère Jean , Kieber Joseph J. , DeLong Alison
Published: June 2006

The roots curl in naphthylphthalamic acid1 (rcn1) mutant of Arabidopsis (Arabidopsis thaliana) has altered auxin transport, gravitropism, and ethylene response, providing an opportunity to analyze the interplay between ethylene and auxin in control of seedling growth. Roots of rcn1 seedlings were previously shown to have altered auxin transport, growth, and gravitropism, while rcn1 hypocotyl elongation exhibited enhanced ethylene response. We have characterized auxin transport and gravitropism phenotypes of rcn1 hypocotyls and have explored the roles of auxin and ethylene in controlling these phenotypes. As in roots, auxin transport is increased in etiolated rcn1 hypocotyls. Hypocotyl gravity response is accelerated, although overall elongation is reduced, in etiolated rcn1 hypocotyls. Etiolated, but not light grown, rcn1 seedlings also overproduce ethylene, and mutations conferring ethylene insensitivity restore normal hypocotyl elongation to rcn1. Auxin transport is unaffected by treatment with the ethylene precursor 1-aminocyclopropane carboxylic acid in etiolated hypocotyls of wild-type and rcn1 seedlings. Surprisingly, the ethylene insensitive2-1 (ein2-1) and ein2-5 mutations dramatically reduce gravitropic bending in hypocotyls. However, the ethylene resistant1-3 (etr1-3) mutation does not significantly affect hypocotyl gravity response. Furthermore, neither the etr1 nor the ein2 mutation abrogates the accelerated gravitropism observed in rcn1 hypocotyls, indicating that both wild-type gravity response and enhanced gravity response in rcn1 do not require an intact ethylene-signaling pathway. We therefore conclude that the RCN1 protein affects overall hypocotyl elongation via negative regulation of ethylene synthesis in etiolated seedlings, and that RCN1 and EIN2 modulate hypocotyl gravitropism and ethylene responses through independent pathways.
Endocytosis Is Essential for Pathogenic Development in the Corn Smut Fungus Ustilago maydis
Authors: Fuchs Uta , Hause Gerd , Schuchardt Isabel , Steinberg Gero
Published: June 2006

It is well established that polarized exocytosis is essential for fungal virulence. By contrast, the contribution of endocytosis is unknown. We made use of a temperature-sensitive mutant in the endosomal target soluble N-ethylmaleimide–sensitive factor attachment protein receptor Yup1 and demonstrate that endocytosis in Ustilago maydis is essential for the initial steps of pathogenic development, including pheromone perception and cell–cell fusion. Furthermore, spore formation and germination were drastically reduced, whereas colonization of the plant was only slightly inhibited. The function of endocytosis in the recognition of mating pheromone through the G protein–coupled pheromone receptor Pra1 was analyzed in greater detail. Biologically active Pra1–green fluorescent protein localizes to the plasma membrane and is constitutively endocytosed. Yup1ts mutants that are blocked in the fusion of endocytic transport vesicles with early endosomes are impaired in pheromone perception and conjugation hyphae formation. This is attributable to an accumulation of Pra1-carrying endocytic vesicles in the cytoplasm and the depletion of the receptor from the membrane. Consistently, strong Pra1 expression rescues the signaling defects in endocytosis mutants, but subsequent cell fusion is still impaired. Thus, we conclude that endocytosis is essential for recognition of the partner at the beginning of the pathogenic program but has additional roles in mating as well as spore formation and germination.
AGL80Is Required for Central Cell and Endosperm Development inArabidopsis
Authors: Portereiko Michael F. , Lloyd Alan , Steffen Joshua G. , Punwani Jayson A. , Otsuga Denichiro , Drews Gary N.
Published: June 2006

During plant reproduction, the central cell of the female gametophyte becomes fertilized to produce the endosperm, a storage tissue that nourishes the developing embryo within the seed. The molecular mechanisms controlling the specification and differentiation of the central cell are poorly understood. We identified a female gametophyte mutant in Arabidopsis thaliana, fem111, that is affected in central cell development. In fem111 female gametophytes, the central cell's nucleolus and vacuole fail to mature properly. In addition, endosperm development is not initiated after fertilization of fem111 female gametophytes. fem111 contains a T-DNA insertion in AGAMOUS-LIKE80 (AGL80). FEM111/AGL80 is a member of the MADS box family of genes that likely encode transcription factors. An AGL80–green fluorescent protein fusion protein is localized to the nucleus. Within the ovule and seed, FEM111/AGL80 is expressed exclusively in the central cell and uncellularized endosperm. FEM111/AGL80 expression is also detected in roots, leaves, floral stems, anthers, and young flowers by real-time RT-PCR. FEM111/AGL80 is required for the expression of two central cell–expressed genes, DEMETER and DD46, but not for a third central cell–expressed gene, FERTILIZATION-INDEPENDENT SEED2. Together, these data suggest that FEM111/AGL80 functions as a transcription factor within the central cell gene regulatory network and controls the expression of downstream genes required for central cell development and function.
Proteomic Analysis of the Eyespot ofChlamydomonas reinhardtiiProvides Novel Insights into Its Components and Tactic Movements
Authors: Schmidt Melanie , Geßner Gunther , Luff Matthias , Heiland Ines , Wagner Volker , Kaminski Marc , Geimer Stefan , Eitzinger Nicole , Reißenweber Tobias , Voytsekh Olga , Fiedler Monika , Mittag Maria , Kreimer Georg
Published: June 2006

Flagellate green algae have developed a visual system, the eyespot apparatus, which allows the cell to phototax. To further understand the molecular organization of the eyespot apparatus and the phototactic movement that is controlled by light and the circadian clock, a detailed understanding of all components of the eyespot apparatus is needed. We developed a procedure to purify the eyespot apparatus from the green model alga Chlamydomonas reinhardtii. Its proteomic analysis resulted in the identification of 202 different proteins with at least two different peptides (984 in total). These data provide new insights into structural components of the eyespot apparatus, photoreceptors, retina(l)-related proteins, members of putative signaling pathways for phototaxis and chemotaxis, and metabolic pathways within an algal visual system. In addition, we have performed a functional analysis of one of the identified putative components of the phototactic signaling pathway, casein kinase 1 (CK1). CK1 is also present in the flagella and thus is a promising candidate for controlling behavioral responses to light. We demonstrate that silencing CK1 by RNA interference reduces its level in both flagella and eyespot. In addition, we show that silencing of CK1 results in severe disturbances in hatching, flagellum formation, and circadian control of phototaxis.