bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport of the leaderless protein Ku on the cell surface of activated monocytes regulates their migratory abilities
Authors: Paupert Jenny , Dauvillier Stéphanie , Salles Bernard , Muller Catherine
Published: May 2007

Recent evidence shows that the DNA repair protein Ku is expressed on the surface of a subset of cells, where it contributes to adhesion and invasion processes, and also to viral or bacterial entry into target cells. Here, we show that Ku was expressed on the cell surface during activation of human monocytes and that its expression was independent of the conventional endoplasmic reticulum (ER)/Golgi secretory pathway. Ku inhibition, by blocking antibodies, decreases the migration of monocytes on fibronectin and laminin. On activation, nuclear Ku seems to move to the periphery of the cell and it shows a punctuate staining in the cytoplasm. The cytoplasmic distribution of Ku was shown to be unaltered by brefeldin A. Protease protection experiments show that Ku is contained within vesicles in activated monocytes. These data support a new role for Ku in the migration of monocytes into tissues, which depends on a tightly regulated pathway of intracellular redistribution.
Ferroelectric-field-induced spin-pinning effect in Pb(Zr0.5Ti0.5)O3∕La0.9Sr0.1MnO3 bilayers
Authors: Liao J. H. , Wu T. B. , Chen Y. T. , Wu J. M.
Published: May 2007

The magnetic properties of Pb(Zr0.5Ti0.5)O3∕La0.9Sr0.1MnO3 bilayers epitaxially grown on Nb-doped SrTiO3 (001) substrate were studied. Bilayers with a fixed Pb(Zr0.5Ti0.5)O3 (PZT) layer thickness of 200nm and different La1−xSrxMnO3 layer thicknesses varying from 10to40nm show a divergence between field-cooled (FC) and zero-field-cooled (ZFC) temperature-dependent magnetization measurements. Moreover, the polarization state of the PZT ferroelectric layer induces a spin-pinning effect causing a variation of the M∕M(10K) ratio in ZFC measurement and the divergent temperature (Td) between FC and ZFC processes. The magnetic hysteresis loops measured in FC and ZFC processes confirm the spin-pinning effect induced from the ferroelectric polarization field, leading to an alternation of the hysteresis loop characteristics for samples polarized with different signs of voltage.
Specific behavior of refractive indices in low-dose He+-implanted LiNbO3 waveguides
Authors: Kostritskii S. M. , Moretti P.
Published: May 2007

Y - or Z- cut LiNbO3 crystals were implanted at room temperature by helium with energy in the MeV range and various doses with a specific care for the 1010–1016ions∕cm2 range. The induced structure defects were investigated by micro-Raman and IR reflectivity. IR Brewster angle technique was applied for detailed measurements on both indices variations in nuclear collision damaged areas. It is established that a transition from point to extended defects occurs at some threshold dose around 1.5×1015ions∕cm2 and that the extraordinary index is increased in a specific dose range around this threshold. A model based on depolarized cluster formation is proposed to explain the difference observed between the changes of ordinary and extraordinary refractive indices.
Relation between the chord length distribution of an infinitely long cylinder and that of its base
Authors: Sukiasian H. S. , Gille Wilfried
Published: May 2007

Chord length distributions are defined for planar and spatial geometric figures. There exist connections between the planar and the spatial cases: The chord length distribution densities (CLDs) of a cylinder B and its base S (the cylinder’s orthogonal cross section) are interrelated by a simple, surveyable integral transformation. From this transformation, it was concluded that the odd moments of the CLD f(x) of S define the leading asymptotic terms of the CLD Aμ(r) of B. The power series of Aμ(r) at r=0 can be traced back to the derivatives of f(x) in the origin. As a general conclusion, there exist different geometric bodies B in R3 with the same CLD Aμ(r). An exact recognition of B via its CLD is not possible. CLDs do not characterize spatial sets. This result is of importance in materials science in order to avoid wrong interpretations in structure research. The new CLD integral transformation has been illustrated in connection with the transitions triangle→triangular rod and rectangle→rectangular rod.
The effect of Mach number on unstable disturbances in shock/boundary-layer interactions
Authors: Yao Y. , Krishnan L. , Sandham N. D. , Roberts G. T.
Published: May 2007

The effect of Mach number on the growth of unstable disturbances in a boundary layer undergoing a strong interaction with an impinging oblique shock wave is studied by direct numerical simulation and linear stability theory (LST). To reduce the number of independent parameters, test cases are arranged so that both the interaction location Reynolds number (based on the distance from the plate leading edge to the shock impingement location for a corresponding inviscid flow) and the separation bubble length Reynolds number are held fixed. Small-amplitude disturbances are introduced via both white-noise and harmonic forcing and, after verification that the disturbances are convective in nature, linear growth rates are extracted from the simulations for comparison with parallel flow LST and solutions of the parabolized stability equations (PSE). At Mach 2.0, the oblique modes are dominant and consistent results are obtained from simulation and theory. At Mach 4.5 and Mach 6.85, the linear Navier-Stokes results show large reductions in disturbance energy at the point where the shock impinges on the top of the separated shear layer. The most unstable second mode has only weak growth over the bubble region, which instead shows significant growth of streamwise structures. The two higher Mach number cases are not well predicted by parallel flow LST, which gives frequencies and spanwise wavenumbers that are significantly different from the simulations. The PSE approach leads to good qualitative predictions of the dominant frequency and wavenumber at Mach 2.0 and 4.5, but suffers from reduced accuracy in the region immediately after the shock impingement. Three-dimensional Navier-Stokes simulations are used to demonstrate that at finite amplitudes the flow structures undergo a nonlinear breakdown to turbulence. This breakdown is enhanced when the oblique-mode disturbances are supplemented with unstable Mack modes.
C
Al
4
X
(XSi,Ge): Molecules with simultaneous planar tetracoordinate carbon, aluminum, and silicon/germanium
Authors: Xie Hong-bin , Ding Yi-hong
Published: May 2007

The authors report the first theoretical study on the hexa-atomic molecules CAl4X (XSi,Ge) at the B3LYP∕6-311++G(2d), MP2∕6-311++G(2d), and CCSD(T)∕6-311++G(3df) (single point) levels. Three low-lying isomers (within 2.0kcal∕mol) can be formally viewed as constructed by one Al+ interacting with the planar CAl3X− at the side Al–X bond (X-1), side Al–Al bond (X-2), and central C atom (X-3). The isomers X-1 and X-2 both have planar structures that include the planar tetracoordinate carbon, aluminum, and silicon/germanium, while the three-dimensional isomer X-3 has the pentacoordinate carbon. The planarity of X-1 and X-2 is ascribed to the ligand five-center two-electron bonding molecular orbital, similar to the orbital responsible for the planarity of CAl3X− (XSi,Ge). Kinetically, the two planar structures X-1 and X-2 can be easily interconverted to each other via the intermediate X-3, indicative of their coexistence. Of particular interest, isomer X-1 represents the first example that simultaneously contains three types of planar centers in a single molecule, to the best of our knowledge. The three low-lying and structurally interesting isomers X-1, X-2, and X-3 await future experimental verification. The present results could enrich the planar chemistry.
Resonance of electrostatically actuated thin-film amorphous silicon microelectromechanical systems microresonators in aqueous solutions: Effect of solution conductivity and viscosity
Authors: Adrega T. , Chu V. , Conde J. P.
Published: May 2007

The resonance of electrostatically actuated thin-film hydrogenated amorphous silicon microbridges in air and immersed in aqueous solutions is measured and characterized. The detection of the resonance frequency of a microbridge operating in aqueous solutions with high electrical conductivities, up to 8 mS/cm, and high viscosities, up to 0.15 Pa s is demonstrated. The range of actuation voltages needed to excite resonance frequencies in the megahertz in these microstructures under aqueous solutions allows electrostatic actuation without electrode screening and electrolysis. Values of the quality factor between 1 and 10 in aqueous solutions will allow the detection of ∼1 pg of added mass to the resonators.
Development of large eddy simulation for modeling of decaying compressible magnetohydrodynamic turbulence
Authors: Chernyshov A. A. , Karelsky K. V. , Petrosyan A. S.
Published: May 2007

The large eddy simulation technique is developed for the study of decaying compressible magnetohydrodynamic turbulence. In the present paper the obtained results of numerical computations for large eddy simulation are compared with the results of direct numerical simulation of three-dimensional compressible magnetohydrodynamic turbulence under various similarity parameters, namely, magnetic Reynolds numbers, hydrodynamic Reynolds numbers, and Mach numbers. The comparison of five subgrid-scale closures of large eddy simulation for the magnetohydrodynamic case is made. The comparison between large eddy simulation and direct numerical simulation is carried out regarding the time evolution of kinetic and magnetic energy, cross helicity, subgrid-scale and molecular dissipations for kinetic and magnetic energy, turbulent intensities and quantities that describe anisotropy of flow, that is, skewness and kurtosis of velocity and magnetic field. It is shown that some subgrid-scale models proposed in the paper provide sufficient dissipation of kinetic and magnetic energy, reduce computational efforts and produce adequate results of magnetohydrodynamic turbulent modeling for various values of similarity parameters of flows.
On the dissipative effects in the electron transport through conducting polymer nanofibers
Authors: Zimbovskaya Natalya A.
Published: May 2007

Here, the author studies the effects of stochastic nuclear motions on the electron transport in doped polymer fibers assuming the conducting state of the material. The author treats conducting polymers as granular metals and applies the quantum theory of conduction in mesoscopic systems to describe the electron transport between metalliclike granules. To analyze the effects of nuclear motions, the author mimics them by a phonon bath and includes electron-phonon interactions in consideration. The results show that the phonon bath plays a crucial part in the intergrain electron transport at moderately low and room temperatures, suppressing the original intermediate state for the resonance electron tunneling and producing new states which support the electron transport. Also, the temperature dependence of the magnitudes of the peaks in the electron transmission corresponding to these new states is analyzed.
Time-dependent density functional theory scheme for efficient calculations of dynamic (hyper)polarizabilities
Authors: Andrade Xavier , Botti Silvana , Marques Miguel A. L. , Rubio Angel
Published: May 2007

The authors present an efficient perturbative method to obtain both static and dynamic polarizabilities and hyperpolarizabilities of complex electronic systems. This approach is based on the solution of a frequency-dependent Sternheimer equation, within the formalism of time-dependent density functional theory, and allows the calculation of the response both in resonance and out of resonance. Furthermore, the excellent scaling with the number of atoms opens the way to the investigation of response properties of very large molecular systems. To demonstrate the capabilities of this method, they implemented it in a real-space (basis-set-free) code and applied it to benchmark molecules, namely, CO, H2O, and para-nitroaniline. Their results are in agreement with experimental and previous theoretical studies and fully validate their approach.
Experimental and theoretical studies of the electronic structure and the ionization and dissociation processes of trifluoromethyl peroxynitrate
Authors: Yao Li , Du Lin , Ge Maofa , Wang Dianxun
Published: May 2007

In this work, we present a complete study of the ionization and dissociation processes for trifluoromethyl peroxynitrate (CF3OONO2). CF3OONO2 was generated by UV photolysis of a mixture of (CF3CO)2O, NO2, and O2. The product was detected and characterized by the photoelectron spectroscopy (PES) and photoionization mass spectroscopy (PIMS). The geometric and electronic structures of CF3OONO2 were investigated by the combination of experiments and the density functional and ab initio calculations. It is worthwhile mentioning that drastic changes occur in the geometry of CF3OONO2 after ionization. Due to the removal of one electron from the O–N σ bond, the COON dihedral angle changes to 180° and as a result, the nonplanar structure becomes planar. And the O–N single bond length increases remarkably, with the positive charge most localized on the NO2 moiety. The experimental first vertical ionization potential is 12.39eV. Based on the calculated bond dissociation energies, the dissociation pathway was predicted. The calculated results explain the ion intensities observed in the photoionization mass spectrum. The dissociation of O–N single bond is found to be the most favored of the possible dissociation paths for CF3OONO2+.
Small angle x-ray scattering measurements of lithographic patterns with sidewall roughness from vertical standing waves
Authors: Wang Chengqing , Jones Ronald L. , Lin Eric K. , Wu Wen-Li , Leu Jim
Published: May 2007

Small angle x-ray scattering (SAXS) measurements are used to quantify the wavelength and amplitude of the sidewall roughness in a lithographic line:space pattern due to vertical standing waves present during the photoresist exposure. Analytic equations are derived to model the x-ray scattering intensity and are used to determine the periodicity and amplitude of the standing wave roughness. The average periodicity, or pitch, and the linewidth were L=422±1nm and w0=148±1nm. The period and amplitude of the standing wave roughness were λs=65±1nm and As=3.0±0.5nm. These results demonstrate the potential of SAXS measurements to quantify nondestructively and quantitatively dimensional deviations from an ideal structure.
Preliminary results of an olive cultivar trial at high density
Authors: De la Rosa R. , León L. , Guerrero N. , Rallo L. , Barranco D.
Published: May 2007

In the last decade, a new concept of olive orchards based on densities of around 2000 trees/ha arose. Its main advantage is the totally mechanised harvesting that drastically reduces the labour needed to collect the crop. In order to evaluate the suitability of 5 olive cultivars (Arbequina, Arbequina IRTA-i·18, Arbosana, Koroneiki, and Fs-17) to this planting system, a comparative trial was set up in 1999 and the initial results are presented in this study. Koroneiki was the most precocious cultivar, but all the rest bear 3 years after planting. Arbequina and Arbosana had the highest accumulated olive yield 6 years after planting. However, the differences in oil content mitigated the variability in yield. Therefore, accumulated oil yields were not significantly different for all the cultivars under study, except for Fs-17. No significant differences were found between Arbequina and its selected clone Arbequina IRTA-i·18 for any of the traits evaluated. The oleic acid content was low in Arbequina and Fs-17, intermediate in Arbosana, and high in Koroneiki. In conclusion, Arbosana showed a similar suitability to Arbequina for high-density orchards due to its high productivity in the first years after planting and its high oleic acid content. In addition, this cultivar is resistant to Spilocea oleagina and Colletotricum spp. in the area of the trial, Córdoba, southern Spain.
Growth responses of cool-season grain legumes to transient waterlogging
Authors: Solaiman Z. , Colmer T. D. , Loss S. P. , Thomson B. D. , Siddique K. H. M.
Published: May 2007

Transient waterlogging reduces the yield of cool-season grain legumes in several parts of the world. The tolerance of grain legumes to waterlogging may vary between and within species. This study investigated the effects of 7 days of waterlogging and subsequent recovery (10 days) on plant growth to evaluate the variation in tolerance among 7 cool-season grain legume species, in sand culture in glasshouse experiments. Additionally waterlogging tolerance of 6 faba bean genotypes was also evaluated. Tolerance to waterlogging as indicated by root and shoot growth (as % of drained controls) was ranked as follows: faba bean > yellow lupin > grass pea > narrow-leafed lupin > chickpea > lentil > field pea. Faba bean produced adventitious roots and aerenchyma leading to increased root porosity (9% gas volume per unit root volume). Among the 6 faba bean genotypes screened, accession 794 showed the best waterlogging tolerance, but it was also the slowest growing accession, which might have contributed to apparent tolerance (i.e. growth as % drained control). It is concluded that waterlogging tolerance in grain legumes varied between and within species, with faba bean being the most tolerant. The variation in tolerance identified within the limited set of faba bean genotypes evaluated suggests scope for further genetic improvement of tolerance in this species.
Fusarium oxysporum Evades I-3-Mediated Resistance Without Altering the Matching Avirulence Gene
Authors: Rep M. , Meijer M. , Houterman P. M. , van der Does H. C. , Cornelissen B. J. C.
Published: May 2007

I-3-Mediated resistance of tomato against Fusarium wilt disease caused by Fusarium oxysporum f. sp. lycopersici depends on Six1, a protein that is secreted by the fungus during colonization of the xylem. Among natural isolates of F. oxysporum f. sp. lycopersici are several that are virulent on a tomato line carrying only the I-3 resistance gene. However, evasion of I-3-mediated resistance by these isolates is not correlated with mutation of the SIX1 gene. Moreover, the SIX1 gene of an I-3-virulent isolate was shown to be fully functional in that i) the gene product is secreted in xylem sap, ii) deletion leads to a further increase in virulence on the I-3 line as well as reduced virulence on susceptible lines, and iii) the gene confers full avirulence on the I-3 line when transferred to another genetic background. Remarkably, all I-3-virulent isolates were of race 1, suggesting a link between the presence of AVR1 and evasion of I-3-mediated resistance.
Harpin of Pseudomonas syringae pv. phaseolicola Harbors a Protein Binding Site
Authors: Li Chun-Mei , Haapalainen Minna , Lee Justin , Nürnberger Thorsten , Romantschuk Martin , Taira Suvi
Published: May 2007

Harpin HrpZ of plant-pathogenic bacterium Pseudomonas syringae elicits a hypersensitive response (HR) in some nonhost plants, but its function in the pathogenesis process is still obscure. HrpZ-interacting proteins were identified by screening a phage-display library of random peptides. HrpZ of the bean pathogen P. syringae pv. Phaseolicola (HrpZPph) shows affinity to peptides with a consensus amino acid motif W(L)ARWLL(G/L). To localize the peptide-binding site, the hrpZPph gene was mutagenized with randomly placed 15-bp insertions, and the mutant proteins were screened for the peptide-binding ability. Mutations that inhibited peptide-binding localized to the central region of hrpZPph, which is separate from the previously determined HR-inducing region. Antiserum raised against one of the hrpZPph-binding peptides recognized small proteins in bean, tomato, parsley, and Arabidopsis thaliana but none in tobacco. On native protein blots, hrpZPph bound to a bean protein with similar pI as the protein recognized by the peptide antiserum. The result suggests a protein-protein interaction between the harpin and a host plant protein, possibly involved in the bacterial pathogenesis.
Involvement of the Small GTPase Rac in the Defense Responses of Tobacco to Pathogens
Authors: Moeder Wolfgang , Yoshioka Keiko , Klessig Daniel F.
Published: May 2007

During the hypersensitive response (HR), plants accumulate reactive oxygen species (ROS) that are likely generated at least in part by an NADPH oxidase similar to that found in mammalian neutrophils. An essential regulator of mammalian NADPH oxidase is the small GTP-binding protein Rac. To investigate whether Rac also regulates the pathogen-induced oxidative burst in plants, a dominant negative form of the rice OsRac1 gene was overexpressed in tobacco carrying the N resistance gene. Following infection with Tobacco mosaic virus (TMV), DN-OsRac1 plants developed smaller lesions than wild-type plants, accumulated lower levels of lipid peroxidation products, and failed to activate expression of antioxidant genes. These results, combined with the demonstration that superoxide and hydrogen peroxide levels were reduced in DN-OsRac1 tobacco developing a synchronous HR triggered by transient expression of the TMV p50 helicase domain or the Pto and AvrPto proteins, suggest that ROS production is impaired. The dominant negative effect of DN-OsRac1 could be rescued by transiently overexpressing the wild-type OsRac1 protein. TMV-induced salicylic acid accumulation also was compromised in DN-OsRac1 tobacco. Interestingly, while systemic acquired resistance to TMV was not impaired, nonhost resistance to Pseudomonas syringae pv. maculicola ES4326 was suppressed. Thus, the effect DN-OsRac1 expression exerts on the resistance signaling pathway appears to vary depending on the identity of the inoculated pathogen.
Glutathione and Homoglutathione Play a Critical Role in the Nodulation Process of Medicago truncatula
Authors: Frendo Pierre , Harrison Judith , Norman Christel , Jiménez María Jesús Hernández , Van de Sype Ghislaine , Gilabert Alain , Puppo Alain
Published: May 2007

Legumes form a symbiotic interaction with bacteria of the Rhizobiaceae family toproduce nitrogen-fixing root nodules under nitrogen-limiting conditions. This process involves the recognition of the bacterial Nod factors by the plant which mediates the entry of the bacteria into the root and nodule organogenesis. We have examined the importance of the low molecular weight thiols, glutathione (GSH) and homoglutathione (hGSH), during the nodulation process in the model legume Medicago truncatula. Using both buthionine sulfoximine, a specific inhibitor of GSH and hGSH synthesis, and transgenic roots expressing GSH synthetase and hGSH synthetase in an antisense orientation, we showed that deficiency in GSH and hGSH synthesis inhibited the formation of the root nodules. This inhibition was not correlated to a modification in the number of infection events or to a change in the expression of the Rhizobium sp.-induced peroxidase rip1, indicating that the low level of GSH or hGSH did not alter the first steps of the infection process. In contrast, a strong diminution in the number of nascent nodules and in the expression of the early nodulin genes, Mtenod12 and Mtenod40, were observed in GSHand hGSH-depleted plants. In conclusion, GSH and hGSH appear to be essential for proper development of the root nodules during the symbiotic interaction.
Barley Rom1 Reveals a Potential Link Between Race-Specific and Nonhost Resistance Responses to Powdery Mildew Fungi
Authors: Freialdenhoven Andreas , Orme James , Lahaye Thomas , Schulze-Lefert Paul
Published: May 2007

The Rar1 gene, identified in the context of race-specific powdery mildew resistance mediated by the Hordeum vulgare (barley) resistance (R) gene Mla12, is required for the function of many R-mediated responses in monoand dicotyledonous plant species. Mla resistance is associated with an oxidative burst and a subsequent cell death reaction of attacked cells. Rar1 mutants are impaired in these responses and, to identify genetic elements which negatively regulate the Mla12-triggered response, we have screened mutagenized Mla12 rar1 mutant populations for restoration of the resistance response. Here we describe the restoration of Mla12-specified resistance (rom1) mutant that restores features of disease resistance to a Blumeria graminis f. sp. hordei isolate expressing the avirulence gene AvrMla12 and retains susceptibility to an isolate lacking AvrMla12. Histochemical analyses show that, in rom1 mutant plants, a whole-cell oxidative burst and cell death response in attacked epidermal cells is restored in the incompatible interaction. Defense responses against tested inappropriate powdery mildews, B. graminis f. sp. tritici and Golovinomyces orontii, were diminished in rar1 mutant plants and enhanced in rom1 mutant plants relative to the wild type. These findings indicate antagonistic activities of Rar1 and Rom1 and reveal their contribution to nonhost and race-specific resistance responses.
Identification of a New Quorum-Sensing-Controlled Virulence Factor in Erwinia carotovora subsp. atroseptica Secreted via the Type II Targeting Pathway
Authors: Corbett Mark , Virtue Sam , Bell Kenneth , Birch Paul , Burr Tom , Hyman Lysbeth , Lilley Kathryn , Poock Susannah , Toth Ian , Salmond George
Published: May 2007

Two-dimensional polyacrylamide gel electrophoresis of the secreted proteins of Erwinia carotovora subsp. atroseptica revealed alow-abundance protein that was identified by mass spectrometry as a homologue of a Xanthomonas campestris avirulence protein with unknown function. The predicted Svx protein has an N-terminal signal sequence and zinc binding-region signature, and the mature protein is post-translationally modified. A 2D difference gel electrophoresis (DIGE) showed that the protein is secreted by the type II (out) secretion apparatus, which is also responsible for the secretion of the major known virulence factors, PelC and CelV. Transcription of the svx gene is under Nacyl- homoserine lactone-mediated quorum-sensing control. The svx gene was inactivated by transposon insertion. The mutant showed a decrease in virulence in potato plant assays, demonstrating a role for Svx in the pathogenicity of E. carotovora subsp. atroseptica. These results show that Svx is a previously unidentified virulence determinant which is secreted by the out machinery and is regulated by quorum sensing, two systems employed by several other virulence factors. Thus, the type II secretory machine is a conduit for virulence factors other than the main pectinnases and cellulase in E. carotovora subsp. atroseptica.
Aldehyde Oxidase (AO) in the Root Nodules of Lupinus albus and Medicago truncatula: Identification of AO in Meristematic and Infection Zones
Authors: Fedorova Elena , Redondo Francisco J. , Koshiba Tomokazu , Pueyo José J. , de Felipe M. Rosario , Lucas M. Mercedes
Published: May 2007

Phytohormones are involved in the organogenesis of legume root nodules. The source of the auxin indole-3-acetic acid (IAA) in nodules has not been clearly determined. We studied the enzyme aldehyde oxidase (AO; EC 1.2.3.1), that catalyzes the last step of IAA biosynthesis in plants, in the nodules of Lupinus albus and Medicago truncatula. Primordia and young lupin nodules and mature M. truncatula nodules showed AO activity bands after native polyacrylamide gel electrophoresis. Gel activity analyses using indole-3-aldehyde as substrate indicated that the nodules of white lupin and M.truncatula have the capability to synthesize IAA via the indole-3-pyruvic acid pathway. Immunolocalization and in situ hybridization experiments revealed that AO is preferentially expressed in the meristematic and the invasion zones in Medicago nodules and in the lateral meristematic zone of Lupinus nodules. High IAA immunolabeling was also detected in the meristematic and invasion zones. Low expression levels and no AO activity were detected in lupin Fix- nodules that displayed restricted growth and early senescence. We propose that local synthesis of IAA in the root nodule meristem and modulation of AO expression and activity are involved in regulation of nodule development.
The LATD Gene of Medicago truncatula Is Required for Both Nodule and Root Development
Authors: Bright Lydia J. , Liang Yan , Mitchell David M. , Harris Jeanne M.
Published: May 2007

The evolutionary origins of legume root nodules are largely unknown. We have identified a gene,LATD, of the model legume Medicago truncatula, that is required for both nodule and root development, suggesting that these two developmental processes may share a common evolutionary origin. The latd mutant plants initiate nodule formation but do not complete it, resulting in immature, non-nitrogen-fixing nodules. Similarly, lateral roots initiate, but remain shortstumps. The primary root, which initially appears to be wild type, gradually ceases growth and forms an abnormal tipthat resembles that of the mutant lateral roots. Infection by the rhizobial partner, Sinorhizobium meliloti, can occur, although infection is rarely completed. Once inside latd mutant nodules, S. meliloti fails to express rhizobial genes associatedwith the developmental transition from free-living bacterium to endosymbiont, such as bacA and nex38. The infecting rhizobia also fail to express nifH and fix nitrogen. Thus, both plant and bacterial development are blocked in latd mutant roots. Based on the latd mutant phenotype, we propose that the wild-type function of the LATD gene is to maintain root meristems. The strong requirement of both nodules and lateral roots for wild-type LATD gene function supports lateral roots as a possible evolutionary origin for legume nodules.
The Pseudomonas syringae avrRpt2 Gene Contributes to Virulence on Tomato
Authors: Lim Melisa T. S. , Kunkel Barbara N.
Published: May 2007

In order to cause disease on plants, gram-negative phytopathogenic bacteria introduce numerous virulence factors into the host cell in order to render host tissue more hospitable for pathogen proliferation. The mode of action of such bacterial virulence factors and their interaction with host defense pathways remain poorly understood. avrRpt2, a gene from Pseudomonas syringae pv. tomato JL1065, has been shown to promote the virulence of heterologous P. syringae strains on Arabidopsis thaliana. However, the contribution of avrRpt2 to the virulence of JL1065 has not been examined previously. We show that a mutant derivative of JL1065 that carries a disruption in avrRpt2 is impaired in its ability to cause disease on tomato (Lycopersicon esculentum), indicating that avrRpt2 also acts as a virulence gene in its native strain on a natural host. The virulence activity of avrRpt2 was detectable on tomato lines that are defective in either ethylene perception or the accumulation of salicylic acid, but could not be detected on a tomato mutant insensitive to jasmonic acid. The enhanced virulence conferred by the expression of avrRpt2 in JL1065 was not associated with the suppression of several defense-related genes induced during the infection of tomato.
Growth Deficiency of a Xanthomonas oryzae pv. oryzae fur Mutant in Rice Leaves Is Rescued by Ascorbic Acid Supplementation
Authors: Subramoni Sujatha , Sonti Ramesh V.
Published: May 2007

Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, a serious disease of rice. A mutation was isolated in the ferric uptake regulator (fur) gene of X. oryzae pv. oryzae and it was shown to result in the production of siderophores in a constitutive manner. The fur mutant is hypersensitive to the metallo-antibiotic streptonigrin, a phenotype that is indicative of intracellular free-iron overload, and also exhibits a slow growth phenotype on rich medium. The fur mutant is virulence deficient, hypersensitive to hydrogen peroxide, and exhibits reduced catalase activity. Exogenous supplementation with ascorbic acid (an antioxidant) rescues the growth deficiency of the fur mutant in rice leaves. The virulence deficiency of the X. oryzae pv. oryzae fur mutant is proposed to be due, at least in part, to an impaired ability to cope with the oxidative stress conditions that are encountered during infection.
Quorum Sensing Regulates Exopolysaccharide Production, Motility, and Virulence in Pseudomonas syringae
Authors: Quiñones Beatriz , Dulla Glenn , Lindow Steven E.
Published: May 2007

The N-acyl homoserine lactone (AHL)-mediated quorumsensing system in the phytopathogen Pseudomonas syringae pv. syringae requires the AHL synthase AhlI and the regulator AhlR, and is additionally subject to regulation by AefR. The contribution of quorum sensing to the expression of a variety of traits expected to be involved in epiphytic fitness and virulence of P. syringae were examined. Both an aefR- mutant and an ahlR- double mutant, deficient in AHL production, were significantly impaired in alginate production and had an increased susceptibility to hydrogen peroxide compared with the wild-type strain. These mutants were hypermotile in culture, invaded leaves more rapidly, and caused an increased incidence of brown spot lesions on bean leaves after a 48-h moist incubation. Interestingly, an aefR- mutant was both the most motile and virulent. Like the wild-type strain, the AHL-deficient mutant strains incited water-soaked lesions on bean pods. However, lesions caused by an ahlI- ahlR- double mutant were larger, whereas those incited by an aefR- mutant were smaller. In contrast, tissue maceration of pods, which occurs at a later stage of infection, was completely abolished in the AHL-deficient mutants. Both the incidence of disease and in planta growth of P. syringae pv. tabaci were greatly reduced in transgenic tobacco plants that produced AHL compared with wild-type plants. These results demonstrate that quorum sensing in P. syringae regulates traits that contribute to epiphytic fitness as well as to distinct stages of disease development during plant infection.
Accumulation of the Long Clas of siRNA Is Associated with Resistance to Plum pox virus in a Transgenic Woody Perennial Plum Tree
Authors: Hily Jean-Michel , Scorza Ralph , Webb Kevin , Ravelonandro Michel
Published: May 2007

We investigated the hallmarks of posttranscription gene silencing (PTGS) in mature plants, embryos, and seedlings of the transgenic plum trees (Prunus sp.) that are resistant to Plum pox virus (PPV). We previously demonstrated that the transgene insert and resistance to PPV were mutually inherited in progeny of line C5. We show here that C5 constitutively produces a short (22 nt) and a long (25 to 26 nt) speciesshort interfering (si)RNA from embryo to mature plant in the absence of PPV inoculation. Unlike siRNA, methylation and transcription of the PPV-coat protein transgene were ‘o;re-set’ following seed germination. Uninoculated transgenic susceptible clones did not display DNA methylation, nor did they produce detectable levels of siRNA. Upon infection, susceptible clones, transgenic or untransformed, did produce siRNA but only the short 22-nt species. These findings show that plum trees respond to virus infection by initiating PTGS-like mechanisms that involve the production of siRNA. We further suggest that high-level virus resistance in transgenic Prunus species requires the production of the long-size class of siRNA. The research adds new insights into PTGS silencing in woody perennial plant species.
Integrity of Nonviral Fragments in Recombinant Tomato bushy stunt virus and Defective Interfering RNA Is Influenced by Silencing and the Type of Inserts
Authors: Zhong Xueyan , Hou Hesheng , Qiu Wenping
Published: May 2007

Recombinant plant viruses have the propensity to remove foreign inserts during replication. This process is virusspecific and occurs in a host-dependent manner. In the present study, we investigated the integrity of foreign inserts in recombinant plant viruses using a model system consisting of Tomato bushy stunt virus (TBSV) and its defective interfering RNA (DI). These were tested in Nicotiana benthamiana plants that were either wild type or transgenic for the green fluorescent protein (GFP) gene. GFP-derived inserts were retained in the recombinant TBSV and DI population that were inoculated onto GFPtransgenic N. benthamiana plants in which silencing of the GFP transgene was initiated, but they were removed from the virus and DIs that were maintained on wild-type plants. A foreign insert derived from an endogenous N. benthamiana gene encoding the H subunit of the magnesium chelatase (NbChlH) was deleted, whereas the fragment of an RNA-dependent RNA polymerase gene (NbRdRP1m) was retained in the recombinant TBSV population. These results demonstrate that the recombination of TBSV to remove nonviral fragments is influenced by silencing and the type of inserts.
An Endopolygalacturonase from Sclerotinia sclerotiorum Induces Calcium-Mediated Signaling and Programmed Cell Death in Soybean Cells
Authors: Zuppini Anna , Navazio Lorella , Sella Luca , Castiglioni Carala , Favaron Francesco , Mariani Paola
Published: May 2007

A basic endopolygalacturonase (PG) isoform, produced early by Sclerotinia sclerotiorum when infecting soybean seedlings, was used to examine the signaling role of the enzyme in aequorin-expressing soybean cells. A cytosolic Ca2+ elevation was induced, with a rapid increase (phase 1) and a very slow decrease (phase 2) of Ca2+ concentration, indicating the involvement of Ca2+ ions in PG signaling. Within 1 h of PG-cell contact a remarkable level of cell death was recorded, significantly higher than the control cell culture turnover. The observed morphological and biochemical changes were indicative of the activation of programmed cell death; in particular, cytochrome c release in the cytoplasm and activation of both caspase 9-like and caspase 3-like proteases were found. When a polygalacturonase-inhibiting protein (PGIP) and the PG were simultaneously applied to cells, both the Ca2+ increase and cell death were annulled. The possible roles of prolonged sustained cytosolic Ca2+ concentrations in inducing cell death and of the PG-PGIP interaction in preventing PG signaling are discussed.
Cation Fluxes Cause Plasma Membrane Depolarization Involved in β-Glucan Elicitor-Signaling in Soybean Roots
Authors: Mithöfer Axel , Ebel Jürgen , Felle Hubert H.
Published: May 2007

Inducible and specific ion fluxes on plasma membranes represent very early events during elicitation of plant cells. The hierarchy of such ion fluxes involved is still unknown. The effect of Phytophthora sojae-derived β-glucan elicitors on the plasma membrane potential as well as on surface K+, Ca2+, and H+ fluxes has been investigated on soybean roots using ion-selective microelectrodes. β-Glucans with different degrees of polymerization transiently depolarized the plasma membrane. The elicitor concentration necessary for half-maximal depolarization closely resembled the corresponding binding affinities of soybean root membranes toward the respective β-glucans. Upon repeated elicitor treatment, the root cells responded partially refractory, suggesting a complex responsiveness of the system. Within the root hair space, characteristic decreasing K+- and Ca2+-free concentrations were induced by the elicitors, probably causing depolarization through the influx of positive charges. Whereas K+ fluxes were inverted after passing the K+ equilibrium (Nernst-) potential, Ca2+ influx continued. No anion fluxes sufficient to account for charge compensation were observed under the same experimental conditions. K+ and Ca2+ fluxes as well as depolarization were inhibited by 100 μM or less of the Ca2+ antagonist La3+. Contrasting other systems, in soybean the main cause for elicitor-induced plasma membrane depolarization is the activation of cation instead of anion fluxes.
The Type III Secretion System of Biocontrol Pseudomonas fluorescens KD Targets the Phytopathogenic Chromista Pythium ultimum and Promotes Cucumber Protection
Authors: Rezzonico Fabio , Binder Christian , Défago Geneviève , Moënne-Loccoz Yvan
Published: May 2007

The type III secretion system (TTSS) is used by Proteobacteria for pathogenic or symbiotic interaction with plant and animal hosts. Recently, TTSSgenes thought to originate from the phytopathogen Pseudomonas syringae were evidenced in Pseudomonas fluorescens KD, which protects cucumber from the oomycete Pythium ultimum (kingdom Chromista/Stramenopila). However, it is not known whether te TTSS contributes to plant protection by the bacterium and, if so, whether it targets the plant or the phytopathogen. Inactivation of TTSS gene hrcV following the insertion of an omega cassette strongly reduced the biocontrol activity of the pseudomonad against P. ultimum on cucumber when compared with the wild type, but had no effect on its root-colonization ability. Analysis of a plasmid-based transcriptional hrpJ′-inaZ reporter fusion revealed that expression in strain KD of the operon containing hrcV was strongly stimulated in vitro and in situ by the oomycete and not by the plant. In vitro, both strain KD and its hrcV mutant reduced the activity level of the pectinase polygalacturonase (a key pathogenicity factor) from P. ultimum, but the reduction was much stronger with the wild type. Together, these results show that the target range of bacterial TTSS is not restricted to plants and animals but also can include members of Chromista/Stramenopila, and suggest that virulence genes acquired horizontally from phytopathogenic bacteria were functionally recycled in biocontrol saprophytic Pseudomonas spp., resulting in enhanced plant protection by the latter.
Resistance Quantitative Trait Loci Originating from Solanum sparsipilum Act Independently on the Sex Ratio of Globodera pallida and Together for Developing a Necrotic Reaction
Authors: Caromel Bernard , Mugniéry Didier , Kerlan Marie-Claire , Andrzejewski Sandra , Palloix Alain , Ellissèche Daniel , Rousselle-Bourgeois Françoise , Lefebvre Véronique
Published: May 2007

Plant resistance to nematodes is related to the ability of the host to reduce the development of nematode juveniles into females. Resistance to the potato cyst nematode (PCN) Globodera pallida, originating from the wild species Solanum sparsipilum, was dissected by a quantitative trait loci (QTL) approach. Two QTL explained 89% of the phenotypic variation. The QTL GpaVsspl on chromosome V displayedthe major effect on the cyst number (coefficient of determination [R2] = 76.6%). It restricted G. pallida development to 16.2% of juveniles, 81.5% of males, and 2.3% of females. The QTL GpaXIsspl chromosome XI displayed a lower effect on the cyst number (R2 = 12.7%). It restricted G. pallida development to 13.8% of juveniles, 35.4% of males, and 50.8% of females. Clones carrying both QTL restricted the nematode development to 58.1% juveniles, 41.1% of males, and 0.8% of females. We demonstrated that potato clones carrying both QTL showed a strong necrotic reaction in roots infected by nematodes, while no such reaction was observed in clones carrying a single QTL. This result underlines the importance to introgress together GpaVsspl and GpaXIsspl into potato cultivars, in order to reduce the density of this quarantine pest in soil and to decrease the risk of selecting overcoming G. pallida subpopulations.
Characterization of the Binding of Diarrheagenic Strains of E. coli to Plant Surfaces and the Role of Curli in the Interaction of the Bacteria with Alfalfa Sprouts
Authors: Jeter Cecelia , Matthysse Ann G.
Published: May 2007

Diarrheagenic Escherichia coli were able to bind to plant surfaces, including alfalfa sprouts and open seed coats, and tomato and Arabidopsis thaliana seedlings incubated in water. The characteristics of the binding differed with the bacterial strain examined. Laboratory K12 strains of E. coli failed to show significant binding to any of the plant surfaces examined, suggesting that some of the genes present and expressed in pathogenic strains and absent or unexpressed in K12 strains may be required for binding to plants. When a plasmid carrying the mlrA gene (a positive regulator of curli biosynthesis) or a plasmid carrying the operons that encode the synthesis of curli (csgA-G) was introduced into K12 strains, the bacteria acquired the ability to bind to sprouts. CsgA mutants of an avian pathogenic E. coli and an O157:H7 strain showed no reduction in their ability to bind to sprouts. Thus, the production of curli appears to be sufficient to allow K12 strains to bind, but curli are not necessary for the binding of pathogenic strains, suggesting that pathogenic strains may have more than one mechanism for binding to plant surfaces.
Induction of Apoptotic Cell Death Leads to the Development of Bacterial Rot Caused by Pseudomonas cichorii
Authors: Kiba Akinori , Sangawa Yasutaka , Ohnishi Kouhei , Yao Nan , Park Pyoyun , Nakayashiki Hitoshi , Tosa Yukio , Mayama Shigeyuki , Hikichi Yasufumi
Published: May 2007

Pseudomonas cichorii is the major causal agent of bacterial rot of lettuce. Collapse and browning symptoms were observed in lettuce leaf tissue from 15 to 24 h after inoculation (HAI) with P.cichorii; superoxide anion generation was detected at 1 to 6 HAI; and cell death was induced at 6 HAI, reaching a maximum at approximately 9 and 12 HAI. Heterochromatin condensation and DNA laddering also were observed within 3 HAI. Pharmacological studies showed that induction of cell death and DNA laddering was closely associated with de novo protein synthesis, protein kinase, intracellular reactive oxygen species, DNase, serine protease, and caspase III-like protease. Moreover, chemicals, which inhibited the induction of cell death and DNA laddering, also suppressed the development of disease symptoms. These results suggest that apoptotic cell death might be closely associated with the development of bacterial rot caused by P. cichorii.
Long- and Short-Chain Plant-Produced Bacterial N-Acyl-Homoserine Lactones Become Components of Phyllosphere, Rhizosphere, and Soil
Authors: Scott Russell A. , Weil Jason , Le Phuong T. , Williams Paul , Fray Rupert G. , von Bodman Susanne B. , Savka Michael A.
Published: May 2007

Two N-acyl-homoserine lactone (acyl-HSL) synthase genes, lasI from Pseudomonas aeruginosa and yenI from Yersinia enterocolitica, were introduced into tobacco, individually and in combination. Liquid chromatograph-tandem mass spectrometry and thin-layer chromatography confirmed products of lasI and yenI activity in single and cotransformants. Cotransformants expressing plastid-localized LasI and YenI synthases produced the major acyl-HSLs for each synthase in all tissues tested. Total acyl-HSL signals accumulated in leaf tissue up to 3 pmol/mg of fresh weight, half as much in stem tissue, and approximately 10-fold less in root tissues. Acyl-HSLs were present in aqueous leaf washes from greenhouse-grown transgenic plants. Transgenic lines grown for 14 days under axenic conditions produced detectable levels of acyl-HSLs in root exudates. Ethyl acetate extractions of rhizosphere and nonrhizosphere soil from transgenically grown plants contained active acyl-HSLs, whereas plant-free soil or rhizosphere and nonrhizosphere soil from wild-type plants lacked detectable amounts of acyl-HSLs. This work shows that bioactive acyl-HSLs are exuded from leaves and roots and accumulate in the phytosphere of plants engineered to produce acyl-HSLs. These data further suggest that plants that are bioengineered to synthesize acyl-HSLs can foster beneficial plant-bacteria communications or deter deleterious interactions. Therefore, it is feasible to use bioengineered plants to supplement soils with specific acyl-HSLs to modulate bacterial phenotypes and plant-associated bacterial community structures.