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Planta
Kinds of Planta Selected AbstractsExtension of a biochemical model for the generalized stoichiometry of electron transport limited C3 photosynthesisPLANT CELL & ENVIRONMENT, Issue 10 2004X. YIN ABSTRACT The widely used steady-state model of Farquhar et al. (Planta 149: 78,90, 1980) for C3 photosynthesis was developed on the basis of linear whole-chain (non-cyclic) electron transport. In this model, calculation of the RuBP-regeneration limited CO2 -assimilation rate depends on whether it is insufficient ATP or NADPH that causes electron transport limitation. A new, generalized equation that allows co-limitation of NADPH and ATP on electron transport is presented herein. The model is based on the assumption that other thylakoid pathways (the Q-cycle, cyclic photophosphorylation, and pseudocyclic electron transport) interplay with the linear chain to co-contribute to a balanced production of NADPH and ATP as required by stromal metabolism. The original model assuming linear electron transport limited either by NADPH or by ATP, predicts quantum yields for CO2 uptake that represent the highest and the lowest values, respectively, of the range given by the new equation. The applicability of the new equation is illustrated for a number of C3 crop species, by curve fitting to gas exchange data in the literature. In comparison with the original model, the new model enables analysis of photosynthetic regulation via the electron transport pathways in response to environmental stresses. [source] Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2 - and O3 - enriched atmospheresPLANT CELL & ENVIRONMENT, Issue 4 2004H. EICHELMANN ABSTRACT Two silver birch (Betula pendula Roth) clones K1659 and V5952 were grown in open-top chambers over 3 years (age 7,9 years). The treatments were increased CO2 concentration (+CO2, 72 Pa), increased O3 concentration (+O3, 2 × ambient O3 with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO2 + O3). Thirty-seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer-operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78,90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b6f, Rubisco specificity and Km (CO2) were not influenced by treatments. Net photosynthetic rate responded to +CO2 with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO2 in clones K1659 and V5952, respectively. The elevated O3 caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O3 had less effect in the presence of +CO2 than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O3 treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress. [source] On the need to incorporate sensitivity to CO2 transfer conductance into the Farquhar,von Caemmerer,Berry leaf photosynthesis modelPLANT CELL & ENVIRONMENT, Issue 2 2004G. J. ETHIER ABSTRACT Virtually all current estimates of the maximum carboxylation rate (Vcmax) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the maximum electron transport rate (Jmax) for C3 species implicitly assume an infinite CO2 transfer conductance (gi). And yet, most measurements in perennial plant species or in ageing or stressed leaves show that gi imposes a significant limitation on photosynthesis. Herein, we demonstrate that many current parameterizations of the photosynthesis model of Farquhar, von Caemmerer & Berry (Planta 149, 78,90, 1980) based on the leaf intercellular CO2 concentration (Ci) are incorrect for leaves where gi limits photosynthesis. We show how conventional A,Ci curve (net CO2 assimilation rate of a leaf ,An, as a function of Ci) fitting methods which rely on a rectangular hyperbola model under the assumption of infinite gi can significantly underestimate Vcmax for such leaves. Alternative parameterizations of the conventional method based on a single, apparent Michaelis,Menten constant for CO2 evaluated at Ci[Km(CO2)i] used for all C3 plants are also not acceptable since the relationship between Vcmax and gi is not conserved among species. We present an alternative A,Ci curve fitting method that accounts for gi through a non-rectangular hyperbola version of the model of Farquhar et al. (1980). Simulated and real examples are used to demonstrate how this new approach eliminates the errors of the conventional A,Ci curve fitting method and provides Vcmax estimates that are virtually insensitive to gi. Finally, we show how the new A,Ci curve fitting method can be used to estimate the value of the kinetic constants of Rubisco in vivo is presented [source] Parameterization of the CO2 and H2O gas exchange of several temperate deciduous broad-leaved trees at the leaf scale considering seasonal changesPLANT CELL & ENVIRONMENT, Issue 2 2003Y. KOSUGI ABSTRACT A combined model to simulate CO2 and H2O gas exchange at the leaf scale was parameterized using data obtained from in situ leaf-scale observations of diurnal and seasonal changes in the CO2 and H2O gas exchange of four temperate deciduous broad-leaved trees using a porometric method. The model consists of a Ball et al. type stomatal conductance submodel [Ball, Woodrow & Berry, pp. 221,224 in Progress in Photosynthesis Research (ed. I. Biggins), Martinus-Nijhoff Publishers, Dordrecht, The Netherlands, 1987] and a Farquhar et al. type biochemical submodel of photosynthesis (Farquhar, von Caemmerer & Berry, Planta 149, 78,90, 1980). In these submodels, several parameters were optimized for each tree species as representative of the quantitative characteristics related to gas exchange. The results show that the seasonal physiological changes of Vcmax25 in the biochemical model of photosynthesis should be used to estimate the long-term CO2 gas exchange. For Rd25 in the biochemical model of photosynthesis and m in the Ball et al. type stomatal conductance model, the difference should be counted during the leaf expansion period. [source] Improved temperature response functions for models of Rubisco-limited photosynthesisPLANT CELL & ENVIRONMENT, Issue 2 2001C. J. Bernacchi ABSTRACT Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steady-state biochemical model of C3 photosynthesis of Farquhar et al. (Planta 149, 78,90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO2 concentrations. From the responses of the rate of CO2 assimilation at a wide range of temperatures, and CO2 and O2 concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C3 photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10,40 °C) necessary for predicting carbon uptake by terrestrial C3 systems. [source] Ustilago maydis spermidine synthase is encoded by a chimeric gene, required for morphogenesis, and indispensable for survival in the hostFEMS YEAST RESEARCH, Issue 6 2009Laura Valdés-Santiago Abstract To analyze the role of spermidine in cell growth and differentiation of Ustilago maydis, the gene encoding spermidine synthase (Spe) was isolated using PCR. We found that the enzyme is encoded by a chimeric bifunctional gene (Spe-Sdh) that also encodes saccharopine dehydrogenase (Sdh), an enzyme involved in lysine biosynthesis. The gene contains a 5, region encoding Spe, followed, without a termination signal or a second initiation codon, by a 3, region encoding Sdh, and directs the synthesis of a single transcript that hybridizes with 3, or 5, regions' probes of the gene. The gene could not be disrupted in a wild-type strain, but only in a mutant defective in the gene encoding ornithine decarboxylase (Odc). Single spe-sdh mutants were isolated after sexual recombination in planta with a compatible wild-type strain. Mutants were auxotrophic for lysine and spermidine, but not for putrescine, and contained putrescine and spermidine, but not spermine. Putrescine in double mutants is probably synthesized from spermidine by the concerted action of polyamine acetyl transferase and polyamine oxidase. spe-sdh mutants were sensitive to stress, unable to carry out the yeast-to-mycelium dimorphic transition, and showed attenuated virulence to maize. These phenotypic alterations were reverted by complementation with the wild-type gene. [source] Essential oil compounds in a historical sample of marjoram (Origanum majorana L., Lamiaceae)FLAVOUR AND FRAGRANCE JOURNAL, Issue 3 2002Johannes Novak Abstract A historical sample of marjoram (Origanum majorana L., Lamiaceae), more than 60 years old, was analysed and its composition compared to standard material from the European herb market. By using a solvent extract of the historical sample, the rearrangements and artefact formation usually occurring during the distillation of marjoram were avoided. The extract contained high amounts of terpinen-4-ol, thus resembling the distilled essential oil more than the solvent extract of the standard sample. So artefact formation in marjoram can also happen in planta in herbs stored for a long time under suboptimal conditions. The high content of carvacrol, normally never present in standard material from cultivation, gave an indication of the heterogeneity of marjoram in former times, and confirmed the opinion that (cultivated) marjoram is a chemovariety selected a long time ago. Copyright © 2002 John Wiley & Sons, Ltd. [source] Molecular detection and , -glucuronidase expression of gus -marked Bacillus subtilis L-form bacteria in developing Chinese cabbage seedlingsJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2003E. Tsomlexoglou Abstract Aim: To detect L-form bacteria in developing Chinese cabbage seedlings. Methods and Results: Stable Bacillus subtilis L-forms were genetically modified to express the gus gene (encoding , -glucuronidase). Germinated seeds of Chinese cabbage were soaked in mannitol based suspensions of the L-form bacteria or with mannitol alone and after washing were grown in aseptic conditions on plant growth medium. Histochemical staining of , -glucuronidase activity (X-gluc) and Polymerase Chain Reaction (PCR) detection of the gus gene were achieved in the L-form associated seedlings. , -Glucuronidase was localized in discrete spots, mainly in the roots with staining, and was also observed in the cotyledons and base of stems. Correlation was observed between PCR detection of the gus gene and histochemical staining with detection in similar tissues. Stable L-form bacteria were non-culturable after their association with plant material. Conclusions: The gus reporter gene system with its associated histological staining for enzyme activity was used successfully for detecting B. subtilis L-form bacteria in plant material. Significance and Impact of the Study: These molecular marked L-forms should provide a specific and sensitive technique for detecting L-form bacteria in planta and offer a method for further understanding the L-form/plant association. [source] Accumulation of Elsinochrome Phytotoxin does not Correlate with Fungal Virulence among Elsinoë fawcettii Isolates in FloridaJOURNAL OF PHYTOPATHOLOGY, Issue 10 2009Li-Yuan Wang Abstract Citrus scab caused by Elsinoë fawcettii is cosmopolitan in humid citrus-growing areas. We have previously demonstrated that production of non-host selective elsinochrome phytotoxin is a prerequisite for fungal full virulence and lesion formation. In this study we evaluated 71 field-collected isolates from Florida for pathogenicity and toxin production and found most of the isolates to be pathogenic to rough lemon, grapefruit and sour orange and able to produce elsinochromes in axenic culture. Elsinochromes were recovered, for the first time, from leaf lesions infected by 21 isolates, including four isolates that did not produce any measurable toxin in culture. There was no direct correspondence between the level of elsinochrome production in culture and virulence among the isolates. However, Elsinoë isolates failed to produce elsinochromes in culture and in planta were non-pathogenic to citrus hosts tested. Several isolates were non-pathogenic or only moderately virulent to the citrus hosts tested even though they could produce elsinochromes in culture, a phenotype not previously described in Florida. [source] The Ustilago maydis Cys2His2 -type zinc finger transcription factor Mzr1 regulates fungal gene expression during the biotrophic growth stageMOLECULAR MICROBIOLOGY, Issue 6 2008Yan Zheng§ Summary The smut fungus Ustilago maydis establishes a biotrophic relationship with its host plant maize to progress through sexual development. Here, we report the identification and characterization of the Cys2His2 -type zinc finger protein Mzr1 that functions as a transcriptional activator during host colonization. Expression of the U. maydis mig2 cluster genes is tightly linked to this phase. Upon conditional overexpression, Mzr1 confers induction of a subset of mig2 genes during vegetative growth and this requires the same promoter elements that confer inducible expression in planta. Furthermore, expression of the mig2-4 and mig2-5 genes during biotrophic growth is strongly reduced in cells deleted in mzr1. DNA-array analysis led to the identification of additional Mzr1-induced genes. Some of these genes show a mig2 -like plant-specific expression pattern and Mzr1 is responsible for their high-level expression during pathogenesis. Mzr1 function requires the b -dependently regulated Cys2His2 -type cell cycle regulator Biz1, indicating that two stage-specific regulators mediate gene expression during host colonization. In spite of a role as transcriptional activator during biotrophic growth, mzr1 is not essential for pathogenesis; however, conditional overexpression interfered with proliferation during vegetative growth and mating ability, caused a cell separation defect, and triggered filamentous growth. We discuss the implications of these findings. [source] NoxA activation by the small GTPase RacA is required to maintain a mutualistic symbiotic association between Epichloë festucae and perennial ryegrassMOLECULAR MICROBIOLOGY, Issue 5 2008Aiko Tanaka Summary Small GTPases of the Rac group play a key regulatory role in NADPH oxidase catalysed production of reactive oxygen species (ROS) in mammals and plants, but very little evidence is available for a corresponding role in fungi. We recently showed that ROS produced by a specific fungal NADPH oxidase isoform, NoxA, are crucial in regulating hyphal morphogenesis and growth in the mutualistic symbiotic interaction between Epichloë festucae and perennial ryegrass. We demonstrate here that E. festucae RacA is required for NoxA activation and regulated production of ROS to maintain a symbiotic interaction. Deletion of racA resulted in decreased ROS production, reduction of radial growth and hyper-branching of the hyphae in culture. In contrast, in planta the racA mutant showed extensive colonization of the host plant, resulting in stunting and precocious senescence of the host plants. Strains expressing a dominant active (DA) allele of RacA had increased ROS production, increased aerial hyphae and reduced radial growth. These results demonstrate that RacA plays a crucial role in regulating ROS production by NoxA, in order to control hyphal morphogenesis and growth of the endophyte in planta. [source] Lipid-induced filamentous growth in Ustilago maydisMOLECULAR MICROBIOLOGY, Issue 3 2004Jana Klose Summary The phytopathogenic fungus Ustilago maydis is obligately dependent on infection of maize to complete the sexual phase of its life cycle. Mating interactions between haploid, budding cells establish an infectious filamentous cell type that invades the host, induces large tumours and eventually forms large masses of black spores. The ability to switch from budding to filamentous growth is therefore critical for infection and completion of the life cycle, although the signals that influence the transition have not been identified from the host or the environment. We have found that growth in the presence of lipids promotes a filamentous phenotype that resembles the infectious cell type found in planta. In addition, the ability of the fungus to respond to lipids is dependent on both the cAMP signalling pathway and a Ras/MAPK pathway; these pathways are known to regulate mating, filamentous growth and pathogenesis in U. maydis. Overall, these results lead us to hypothesize that lipids may represent one of the signals that promote and maintain the filamentous growth of the fungus in the host environment. [source] SGT1 positively regulates the process of plant cell death during both compatible and incompatible plant,pathogen interactionsMOLECULAR PLANT PATHOLOGY, Issue 5 2010KERI WANG SUMMARY SGT1 (suppressor of G2 allele of Skp1), an interactor of SCF (Skp1-Cullin-F-box) ubiquitin ligase complexes that mediate protein degradation, plays an important role at both G1,S and G2,M cell cycle transitions in yeast, and is highly conserved throughout eukaryotes. Plant SGT1 is required for both resistance (R) gene-mediated disease resistance and nonhost resistance to certain pathogens. Using virus-induced gene silencing (VIGS) in Nicotiana benthamiana, we demonstrate that SGT1 positively regulates the process of cell death during both host and nonhost interactions with various pathovars of Pseudomonas syringae. Silencing of NbSGT1 in N. benthamiana plants delays the induction of hypersensitive response (HR)-mediated cell death against nonhost pathogens and the development of disease-associated cell death caused by the host pathogen P. syringae pv. tabaci. Our results further demonstrate that NbSGT1 is required for Erwinia carotovora - and Sclerotinia sclerotiorum -induced disease-associated cell death. Overexpression of NbSGT1 in N. benthamiana accelerates the development of HR during R gene-mediated disease resistance and nonhost resistance. Our data also indicate that SGT1 is required for pathogen-induced cell death, but is not always necessary for the restriction of bacterial multiplication in planta. Therefore, we conclude that SGT1 is an essential component affecting the process of cell death during both compatible and incompatible plant,pathogen interactions. [source] Contributions of the effector gene hopQ1-1 to differences in host range between Pseudomonas syringae pv. phaseolicola and P. syringae pv. tabaciMOLECULAR PLANT PATHOLOGY, Issue 6 2009PATRIZIA FERRANTE SUMMARY To study the role of type III-secreted effectors in the host adaptation of the tobacco (Nicotiana sp.) pathogen Pseudomonas syringae pv. tabaci, a selection of seven strains was first characterized by multilocus sequence typing (MLST) to determine their phylogenetic affinity. MLST revealed that all strains represented a tight phylogenetic group and that the most closely related strain with a completely sequenced genome was the bean (Phaseolus vulgaris) pathogen P. syringae pv. phaseolicola 1448A. Using primers designed to 21 P. syringae pv. phaseolicola 1448A effector genes, it was determined that P. syringae pv. phaseolicola 1448A shared at least 10 effectors with all tested P. syringae pv. tabaci strains. Six of the 11 effectors that failed to amplify from P. syringae pv. tabaci strains were individually expressed in one P. syringae pv. tabaci strain. Although five effectors had no effect on phenotype, growth in planta and disease severity of the transgenic P. syringae pv. tabaci expressing hopQ1-1Pph1448A were significantly increased in bean, but reduced in tobacco. We conclude that hopQ1-1 has been retained in P. syringae pv. phaseolicola 1448A, as this effector suppresses immunity in bean, whereas hopQ1-1 is missing from P. syringae pv. tabaci strains because it triggers defences in Nicotiana spp. This provides evidence that fine-tuning effector repertoires during host adaptation lead to a concomitant reduction in virulence in non-host species. [source] Putative lipoproteins identified by bioinformatic genome analysis of Leifsonia xyli ssp. xyli, the causative agent of sugarcane ratoon stunting diseaseMOLECULAR PLANT PATHOLOGY, Issue 1 2007IAIN C. SUTCLIFFE SUMMARY Leifsonia xyli ssp. xyli is the causative agent of ratoon stunting disease, a major cause of economic loss in sugarcane crops. Understanding of the biology of this pathogen has been hampered by its fastidious growth characteristics in vitro. However, the recent release of a genome sequence for this organism has allowed significant novel insights. Further to this, we have performed a bioinformatic analysis of the lipoproteins encoded in the L. xyli genome. These analyses suggest that lipoproteins represent c. 2.0% of the L. xyli predicted proteome. Functional analyses suggest that lipoproteins make an important contribution to the physiology of the pathogen and may influence its ability to cause disease in planta. [source] Protein kinase A subunits of the ascomycete pathogen Mycosphaerella graminicola regulate asexual fructification, filamentation, melanization and osmosensingMOLECULAR PLANT PATHOLOGY, Issue 6 2006RAHIM MEHRABI SUMMARY As in many fungi, asexual reproduction of Mycosphaerella graminicola in planta is a complex process that requires proper differentiation of the infectious hyphae in the substomatal cavities of foliar tissue before pycnidia with conidia can be formed. In this study, we have investigated the role of the cAMP signalling pathway in development and pathogenicity of this pathogen by disruption of the genes encoding the catalytic (designated MgTpk2) and regulatory subunit (designated MgBcy1) of protein kinase A. The MgTpk2 and MgBcy1 mutants showed altered phenotypes in vitro when grown under different growth conditions. On potato dextrose agar (PDA), MgBcy1 mutants showed altered osmosensitivity and reduced melanization, whereas the MgTpk2 mutants showed accelerated melanization when compared with the M. graminicola IPO323 wild-type strain and ectopic transformants. MgTpk2 mutants also secreted a dark-brown pigment into yeast glucose broth medium. In germination and microconidiation assays, both mutants showed a germination pattern similar to that of the controls on water agar, whereas on PDA filamentous growth of MgTpk2 mutants was impaired. Pathogenicity assays showed that the MgTpk2 and MgBcy1 mutants were less virulent as they caused only limited chlorotic and necrotic symptoms at the tips of the inoculated leaves. Further analyses of the infection process showed that MgTpk2 and MgBcy1 mutants were able to germinate, penetrate and colonize mesophyll tissue, but were unable to produce the asexual fructifications, which was particularly due to inappropriate differentiation during the late stage of this morphogenesis-related process. [source] Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum) genes expressed during infection of cotton (Gossypium hirsutum),MOLECULAR PLANT PATHOLOGY, Issue 2 2006HELEN G. MCFADDEN SUMMARY We sought to identify Fusarium oxysporum f. sp. vasinfectum (Fov) genes that may be associated with pathogenicity. Initially we utilized microarray and Q-PCR technology to identify Fov genes expressed in root and hypocotyl tissues during a compatible infection of cotton. We identified 218 fungal clones representing 174 Fov non-redundant genes as expressed in planta. The majority of the expressed sequences were expressed in infected roots, with only six genes detected in hypocotyl tissue. The Fov genes identified were predominately of unknown function or associated with fungal growth and energy production. We then analysed the expression of the identified fungal genes in infected roots and in saprophytically grown mycelia and identified 11 genes preferentially expressed in plant tissue. A putative oxidoreductase gene (with homology to AtsC) was found to be highly preferentially expressed in planta. In Agrobacterium tumefaciens, AtsC is associated with virulence. Inoculation of a susceptible and a partially resistant cotton cultivar with either a pathogenic or a non-pathogenic isolate of Fov revealed that the expression of the Fov AtsC homologue was associated with pathogenicity and disease symptom formation. [source] Claviceps purpurea: molecular aspects of a unique pathogenic lifestyleMOLECULAR PLANT PATHOLOGY, Issue 5 2004PAUL TUDZYNSKI SUMMARY Claviceps purpurea is a ubiquitous pathogen of cereals and grasses, causing Ergot disease, which results in substitution of grains by sclerotia. These overwintering structures contain ergot-alkaloids, which can cause severe intoxication in mammals. C. purpurea is an interesting model system for the study of host,pathogen interaction. It displays strict organ specificity, attacking exclusively young grass ovaries. It is optimally adapted to this special niche of infection, probably by mimicry of pollen tubes: there are no resistance genes known, and no effective resistance reactions can be detected in the early steps of infection. In this early phase of host tissue colonization the fungus shows directed, almost unbranched growth towards the base of the ovary. Thus, C. purpurea represents one of the few systems in which directed growth in filamentous fungi can be studied. Finally, the fungus behaves as a true biotroph in planta, although it can be easily grown in axenic culture. We describe here the tools available to study this interesting pathogen, report on recent molecular investigations concerning the role of cell-wall-degrading enzymes and of reactive oxygen species in this specialized interaction, and present an update of the signalling cascades involved in early events of pathogenesis. [source] Characterization of a developmentally regulated amino acid transporter (AAT1p) of the rust fungus Uromyces fabaeMOLECULAR PLANT PATHOLOGY, Issue 1 2002Christine Struck summary In the rust fungus Uromyces fabae, invasion of the host plant and haustorium formation are accompanied by the activation of many genes (PIGs =in planta induced genes). In addition to the previously described AAT2 (PIG2), AAT1 (PIG27) was found to encode a protein with a high similarity to fungal amino acid permeases. AAT1 transcripts are present in germinated hyphae and throughout the mycelium later in the infection process, but occur at the highest levels in haustoria. Expression of AAT1p in a histidine uptake-defective yeast mutant revealed energy-dependent transport of 14C-histidine, with a KM value of 25.8 µm. In addition, complementation analysis revealed AAT1 -dependent transport for lysine. Using Xenopus oocytes as expression system, AAT1p-dependent symport of protons with a broad spectrum of amino acids was observed, with the highest activities obtained with histidine and lysine. These results confirm that in rust fungi, the expression of amino acid transporters is developmentally regulated and occurs preferentially in the parasitic phase of development. [source] Requirements for cell-to-cell movement of Barley stripe mosaic virus in monocot and dicot hostsMOLECULAR PLANT PATHOLOGY, Issue 2 2001Diane M. Lawrence Summary The Barley stripe mosaic virus (BSMV) RNAß genome contains a series of overlapping open reading frames termed the triple gene block. The three most abundant proteins, ,b, ,c and ,d, have been shown to have essential roles in infectivity, but their function in cell-to-cell movement has not previously been unambiguously defined, nor has the role of a minor translational read-through protein, ,d, been characterized. We have now examined the direct involvement of each of these proteins in cell-to-cell movement in planta by engineering fusions of the green fluorescent protein (GFP) to a cysteine-rich regulatory protein designated ,b. Microscopic examination of inoculated and systemically infected barley and oat leaves revealed high levels of fluorescence that moved rapidly through the compact striate vascular tissue without infecting epidermal cells. In contrast, a radial pattern of fluorescence spread through a large number of epidermal and mesophyll cells before entry into the reticulate vascular tissue of the dicot hosts Nicotiania benthamiana and Chenopodium amaranticolor. Mutational analyses indicated that the ,b, ,c and ,d proteins are each essential for cell-to-cell movement in local lesion and systemic hosts, whereas the ,d, protein is dispensable. Collectively, these results demonstrate conclusively that the three major triple gene block-encoded proteins act in concert to mediate cell-to-cell movement of BSMV. [source] The distribution and expression of a biotrophy-related gene, CIH1, within the genus ColletotrichumMOLECULAR PLANT PATHOLOGY, Issue 4 2000Sarah E. Perfect During the biotrophic phase of the infection process of the hemibiotrophic anthracnose fungus Colletotrichum lindemuthianum, an intracellular hypha develops within epidermal cells of its host, Phaseolus vulgaris. This is followed by the formation of secondary hyphae during the necrotrophic phase. Previous work using a monoclonal antibody, UB25, has identified a glycoprotein that is specific to the interfacial matrix that forms between the wall of the intracellular hypha and the invaginated host plasma membrane. The gene encoding the protein identified by UB25 was cloned by immunoscreening and designated CIH1. The predicted amino acid sequence revealed a proline-rich glycoprotein, and biochemical evidence suggested that it formed a cross-linked structure at the biotrophic interface. Although CIH1 is a fungal gene, its product has several similarities to plant cell wall proteins. In this paper, we have surveyed the distribution and expression of CIH1 within the genus Colletotrichum, encompassing both necrotrophic and hemibiotrophic species. The results show that homologues of the CIH1 gene are present in all the Colletotrichum species tested. Northern blot studies of the time course of the infection process in planta have shown that CIH1 is expressed by both C. lindemuthianum in bean and C. trifolii in alfalfa during the biotrophic phase of fungal development. Immunofluorescence labelling of infected epidermal strips with UB25 revealed that the intracellular hyphae formed by C. destructivum as it infects alfalfa were specifically labelled in a similar way to those formed by C. lindemuthianum in bean. Northern and Western analysis showed that CIH1 was also expressed by C. lindemuthianum in vitro, though not constitutively. Overall, the evidence supports a role for CIH1 in biotrophy within the genus Colletotrichum. [source] Inhibitors of plant invertases do not affect the structurally related enzymes of fructan metabolismNEW PHYTOLOGIST, Issue 3 2009Ute Kusch Summary ,,Plant fructan active enzymes (FAZYs), including the enzymes involved in inulin metabolism, namely sucrose:sucrose 1-fructosyltransferase (1-SST; EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (1-FFT; EC 2.4.1.100) and fructan 1-exohydrolase (1-FEH; EC 3.2.1.153), are evolutionarily related to acid invertases (AIs), that is, plant cell wall invertase (CWI) and vacuolar invertase (VI). Acid invertases are post-translationally controlled by proteinaceous inhibitors. Whether FAZYs are subject to similar controls is not known. ,,To probe their possible interactions with invertase inhibitors, we transiently expressed chicory (Cichorium intybus) FAZYs, as well as several previously characterized invertase inhibitors from nonfructan species, and the C. intybus cell wall/vacuolar inhibitor of fructosidase (CiC/VIF), a putative invertase inhibitor of a fructan-accumulating plant, in leaves of Nicotiana benthamiana. ,,Leaf extracts containing recombinant, enzymatically active FAZYs were used to explore the interaction with invertase inhibitors. Neither heterologous inhibitors nor CiC/VIF affected FAZY activities. CiC/VIF was confirmed as an AI inhibitor with a stronger effect on CWI than on VI. Its expression in planta was developmentally regulated (high in taproots, and undetectable in leaves and flowers). In agreement with its target specificities, CiC/VIF was associated with the cell wall. ,,It is concluded that subtle structural differences between AIs and FAZYs result in pronounced selectivity of inhibitor action. [source] Functional analysis of the heavy metal binding domains of the Zn/Cd-transporting ATPase, HMA2, in Arabidopsis thalianaNEW PHYTOLOGIST, Issue 1 2009Chong Kum Edwin Wong Summary ,,The Zn/Cd-transporting ATPase, HMA2, has N- and C-terminal domains that can bind Zn ions with high affinity. Mutant derivatives were generated to determine the significance of these domains to HMA2 function in planta. ,,Mutant derivatives, with and without a C-terminal GFP tag, were expressed from the HMA2 promoter in transgenic hma2,hma4, Zn-deficient, plants to test for functionality. ,,A deletion mutant lacking the C-terminal 244 amino acids rescued most of the hma2,hma4 Zn-deficiency phenotypes with the exception of embryo or seed development. Root-to-shoot Cd translocation was fully rescued. The GFP-tagged derivative was partially mis-localized in the root pericycle cells in which it was expressed. Deletion derivatives lacking the C-terminal 121 and 21 amino acids rescued all phenotypes and localized normally. N-terminal domain mutants localized normally but failed to complement the hma2,hma4 phenotypes. ,,These observations suggest that the N-terminal domain of HMA2 is essential for function in planta while the C-terminal domain, although not essential for function, may contain a signal important for the subcellular localization of the protein. [source] Toxicity and nicotinic acetylcholine receptor interaction of imidacloprid and its metabolites in Apis mellifera (Hymenoptera: Apidae)PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2001Ralf Nauen Abstract Acute oral and contact toxicity tests of imidacloprid, an insecticide acting agonistically on nicotinic acetylcholine receptors (nAChR), to adult honeybees, Apis mellifera L var carnica, were carried out by seven different European research facilities. Results indicated that the 48-h oral LD50 of imidacloprid is between 41 and >81,ng per bee, and the contact LD50 between 49 and 102,ng per bee. The ingested amount of imidacloprid-containing sucrose solution decreased with increasing imidacloprid concentrations and may be attributed to dose-related sub-lethal intoxication symptoms or to antifeedant responses. Some previously reported imidacloprid metabolites occuring at low levels in planta after seed dressing, ie olefine-, 5-OH- and 4,5-OH-imidacloprid, showed lower oral LD50 values (>36, >49 and 159,ng per bee, respectively) compared with the concurrently tested parent molecule (41,ng per bee). The urea metabolite and 6-chloronicotinic acid (6-CNA) exhibited LD50 values of >99,500 and >121,500,ng per bee, respectively. The pharmacological profile of the [3H]imidacloprid binding site in honeybee head membrane preparations is consistent with that anticipated for a nAChR. IC50 values for the displacement of [3H]imidacloprid by several metabolites such as olefine, 5-OH-, 4,5-OH-imidacloprid, urea and 6-CNA were 0.45, 24, 6600, >100,000, and >100,000,nM, respectively. Displacement of [3H]imidacloprid by imidacloprid revealed an IC50 value of 2.9,nM, thus correlating well with the observed acute oral toxicity of the compounds in honeybees. Neurons isolated from the antennal lobe of A mellifera and subjected to whole-cell voltage clamp electrophysiology responded to the application of 100,µM acetylcholine with a fast inward current of between 30 and 1600 pA at ,70,mV clamp potential. Imidacloprid and two of the metabolites (olefine- and 5-OH-imidacloprid) acted agonistically on these neurons, whereas the others did not induce currents at test conencentrations up to 3,mM. The electrophysiological data revealed Hill coefficients of approximately 1, indicating a single binding site responsible for an activation of the receptor and no direct cooperativity or allosteric interaction with a second binding site. © 2001 Society of Chemical Industry [source] Disease resistance conferred by the expression of a gene encoding a synthetic peptide in transgenic cotton (Gossypium hirsutum L.) plantsPLANT BIOTECHNOLOGY JOURNAL, Issue 6 2005Kanniah Rajasekaran Summary Fertile, transgenic cotton plants expressing the synthetic antimicrobial peptide, D4E1, were produced through Agrobacterium -mediated transformation. PCR products and Southern blots confirmed integration of the D4E1 gene, while RT-PCR of cotton RNA confirmed the presence of D4E1 transcripts. In vitro assays with crude leaf protein extracts from T0 and T1 plants confirmed that D4E1 was expressed at sufficient levels to inhibit the growth of Fusarium verticillioides and Verticillium dahliae compared to extracts from negative control plants transformed with pBI-d35S,- uidA-nos (CGUS). Although in vitro assays did not show control of pre-germinated spores of Aspergillus flavus, bioassays with cotton seeds in situ or in planta, inoculated with a GFP-expressing A. flavus, indicated that the transgenic cotton seeds inhibited extensive colonization and spread by the fungus in cotyledons and seed coats. In planta assays with the fungal pathogen, Thielaviopsis basicola, which causes black root rot in cotton, showed typical symptoms such as black discoloration and constriction on hypocotyls, reduced branching of roots in CGUS negative control T1 seedlings, while transgenic T1 seedlings showed a significant reduction in disease symptoms and increased seedling fresh weight, demonstrating tolerance to the fungal pathogen. Significant advantages of synthetic peptides in developing transgenic crop plants that are resistant to diseases and mycotoxin-causing fungal pathogens are highlighted in this report. [source] Electrophysiological characterization of pathways for K+ uptake into growing and non-growing leaf cells of barleyPLANT CELL & ENVIRONMENT, Issue 12 2009VADIM VOLKOV ABSTRACT Potassium is a major osmolyte used by plant cells. The accumulation rates of K+ in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K+ uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley (Hordeum vulgare L.). A time-dependent inward-rectifying K+ -selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na+ over K+. Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K+ in cells calculated from patch clamp current,voltage curves exceeded rates calculated from membrane potential and K+ concentrations of cells measured in planta by factor 2.5,2.7 at physiological apoplastic K+ concentrations (10,100 mm). It is concluded that under these conditions, K+ accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K+ accumulation. [source] Efficacy of phosphonic acid, metalaxyl-M and copper hydroxide against Phytophthora ramorum in vitro and in plantaPLANT PATHOLOGY, Issue 1 2009M. Garbelotto The ability of metalaxyl-M, phosphonic acid in the form of phosphonate, and copper hydroxide to inhibit different stages in the life cycle of Phytophthora ramorum, the causal agent of sudden oak death (SOD), was tested in vitro using 12 isolates from the North American forest lineage. In addition, experiments were conducted in planta to study the ability of phosphonic acid injections and metalaxyl-M drenches to control pathogen growth on saplings of California coast live oak (Quercus agrifolia), and of copper hydroxide foliar sprays to control infection of California bay laurel (Umbellularia californica) leaves. Phytophthora ramorum was only moderately sensitive to phosphonic acid in vitro, but was highly sensitive to copper hydroxide. In planta experiments indicated the broad efficacy of phosphonic acid injections and of copper hydroxide sprays in preventing growth of P. ramorum in oaks and bay laurels, respectively. Finally, although metalaxyl-M was effective in vitro, drenches of potted oak trees using this active ingredient were largely ineffective in reducing the growth rate of the pathogen in planta. [source] The oldest fungicide and newest phytoalexin , a reappraisal of the fungitoxicity of elemental sulphurPLANT PATHOLOGY, Issue 3 2004J. S. Williams Elemental sulphur (S0) is man's oldest fungicide. In biological systems it is formed by certain specialized prokaryotes but the element has rarely been found in eukaryotes. The recent discovery that certain plant species from diverse families produce S0 as a localized component of active defence to vascular pathogens, and that S0 is constitutive in some crucifers, led to this review. Because of the age and relative inaccessibility of some of the past literature and the inconsistency in the methods used, the spectrum of activity and the toxicity of S0 are reassessed here. Interpretation of bioassays of this and other hydrophobic compounds are offered. Also, brief coverage is given to the history of S0 use and its suggested mode(s) of action. The element's possible role in defence and the form, location and levels in planta are considered. Sulphur is one of many S-containing defence-related compounds and it is ironic that sulphur deficiency has recently become a widespread nutrient disorder in crops, largely due to restrictions on fossil fuel burning. The problem is being addressed by sulphur application, but the future manipulation of genes for sulphate uptake and sulphur biosynthesis are likely goals. [source] Secretome analysis of differentially induced proteins in rice suspension-cultured cells triggered by rice blast fungus and elicitorPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 5 2009Sun Tae Kim Abstract Secreted proteins were investigated in rice suspension-cultured cells treated with rice blast fungus Magnaporthe grisea and its elicitor using biochemical and 2-DE coupled with MS analyses followed by their in planta mRNA expression analysis. M. grisea and elicitor successfully interacted with suspension-cultured cells and prepared secreted proteins from these cultures were essentially intracellular proteins free. Comparative 2-D gel analyses identified 21 differential protein spots due to M. grisea and/or elicitor over control. MALDI-TOF-MS and ,LC-ESI-MS/MS analyses of these protein spots revealed that most of assigned proteins were involved in defense such as nine chitinases, two germin A/oxalate oxidases, five domain unknown function 26 (DUF 26) secretory proteins, and ,-expansin. One chitin binding chitinase protein was isolated using chitin binding beads and strong enzymatic activity was identified in an in-gel assay. Interestingly, their protein abundance correlated well at transcript levels in elicitor-treated cultures as judged by semi-quantitative RT-PCR. Each identified differentially expressed protein group was compared at transcript levels in rice leaves inoculated with incompatible (KJ401) and compatible (KJ301) races of M. grisea. Time-course profiling revealed their inductions were stronger and earlier in incompatible than compatible interactions. Identified secreted proteins and their expression correlation at transcript level in suspension-cultured cells and also in planta suggest that suspension-cultured cells can be useful to investigate the secretome of rice blast,pathogen interactions. [source] A SELDI-TOF MS procedure for the detection, quantitation, and preliminary characterization of low-molecular-weight recombinant proteins expressed in transgenic plantsPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 2 2009M. Amine Badri Abstract We describe a SELDI-TOF MS procedure for the rapid detection and quantitation of low-molecular-weight recombinant proteins expressed in plants. Transgenic lines of potato (Solanum tuberosum L.) expressing the clinically useful protein bovine aprotinin or the cysteine protease inhibitor corn cystatin II were generated by Agrobacterium tumefaciens -mediated transformation, and then used as test material for the analyses. Real-time RT-PCR amplifications and detection of the recombinant proteins by immunoblotting were first conducted for transformed potato lines accumulating the proteins in different cell compartments. Both proteins were found at varying levels in leaves, depending on their final cellular destination and transgene expression rate. These conclusions drawn from standard immunodetection assays were easily confirmed by SELDI-TOF MS comparative profiling, after immobilizing the leaf proteins of control and transformed lines on protein biochips for weak cationic exchange. This procedure, carried out in less than 2,h, allows for the rapid comparison of recombinant protein levels in transgenic plant lines. The molecular weight of immobilized proteins can also be determined directly from the MS spectra, thus providing a simple way to assess the structural integrity and homogeneity of recombinant proteins in planta, and to identify the most suitable cellular compartments for their heterologous production. [source] | |||||||||||||