bluuebunny/crossref_metadata_2025_split huggingface dataset:
Candida glabrata STE12 is required for wild‐type levels of virulence and nitrogen starvation induced filamentation
Authors: Calcagno Ana‐Maria , Bignell Elaine , Warn Peter , Jones Michael D. , Denning David W. , Mühlschlegel Fritz A. , Rogers Thomas R. , Haynes Ken 
Published: November 2003

SummaryThe highly conserved fungal Ste12 transcription factor family of proteins play critical roles in the regulation of many cellular processes including mating, cell wall biosynthesis, filamentation and invasive growth. They are also important mediators of fungal virulence. The Candida glabrata STE12 homologue was cloned. The encoded protein has a single DNA binding homeodomain but lacks both a C2H2 zinc finger DNA binding domain and an apparent Dig1/Dig2 regulatory motif. Candida glabrata STE12 can functionally complement the nitrogen starvation induced filamentation and mating defects of Saccharomyces cerevisiae ste12 mutants. We also show that C. glabrata STE12 is required for nitrogen starvation‐induced filamentation as ste12 mutants rarely produce pseudohyphae on nitrogen depeleted media. Finally we describe a novel murine model of C. glabrata systemic disease and use this to demonstrate that C. glabrata ste12 mutants, although still able to cause disease, are attenuated for virulence compared with STE12 reconstituted strains. Candida glabrata STE12 is therefore the first virulence factor encoding gene to be described in this increasingly important fungal pathogen.
An anti‐repression Fur operator upstream of the promoter is required for iron‐mediated transcriptional autoregulation in Helicobacter pylori
Authors: Delany Isabel , Spohn Gunther , Rappuoli Rino , Scarlato Vincenzo 
Published: November 2003

SummaryThe Fur protein acts as a regulator of iron‐dependent gene transcription in bacteria. In Helicobacter pylori, Fur regulates iron‐activated and iron‐repressed promoters. It also acts as an autoregulatory rheostat of transcription to fine‐tune its own expression in response to iron by binding to three operators at its own promoter Pfur . Using biochemical and genetic analyses, here we show that the distal upstream operator III (centred at −110) is essential for iron regulation of Pfur and functions as an anti‐repression site that is bound by the iron‐free form of Fur to induce transcription. Furthermore, operator I (centred at −50) may have a dual role both as a high‐affinity binding site for Fur and as an UP element. We propose that its role is ensuring that Fur expression is not repressed below a minimum threshold level. Our data supports a novel promoter architecture and mechanism of regulation by Fur.
The nuclear actin‐related protein Act3p/Arp4p of Saccharomyces cerevisiae is involved in transcription regulation of stress genes
Authors: Görzer Irene , Schüller Christoph , Heidenreich Erich , Krupanska Ludmila , Kuchler Karl , Wintersberger Ulrike 
Published: November 2003

SummaryA mutational analysis of the essential nuclear actin‐related protein of Saccharomyces cerevisiae, Act3p/Arp4p, was performed. The five residues chosen for substitution were amino acids conserved between actin and Act3p/Arp4p, the tertiary structure of which most probably resembles that of actin. Two thermosensitive (ts) mutants, a single and a double point mutant, and one lethal double point mutant were obtained. Both ts mutants were formamide‐sensitive which supports a structural relatedness of Act3p/Arp4p to actin; they were also hypersensitive against hydroxyurea and ultraviolet irradiation pointing to a possible role of Act3p/Arp4p in DNA replication and repair. Their ‘suppressor of Ty’ (SPT) phenotype, ob‐served with another ts mutant of Act3p/Arp4p before, suggested involvement of Act3p/Arp4p in transcription regulation. Accordingly, genome‐wide expression profiling revealed misregulated transcription in a ts mutant of a number of genes, among which increased expression of various stress‐responsive genes (many of them requiring Msn2p/Msn4p for induction) was the most salient result. This provides an explanation for the mutant's enhanced resistance to severe thermal and oxidative stress. Thus, Act3p/Arp4p takes an important part in the repression of stress‐induced genes under non‐stress conditions.
From nose to lung: the regulation behind Streptococcus pneumoniae virulence factors
Authors: Hava David L. , LeMieux Julianna , Camilli Andrew 
Published: November 2003

Summary Streptococcus pneumoniae probably possesses a redundant set of factors required for colonization of the nasopharynx and invasive disease, because of its strict relationship with its human host and relatively small genome size (∼2.1 Mb). Nevertheless, transcriptional regulation of genes encoding factors required for in vivo growth is predicted to be important on two fronts: in the transition from carriage to invasive disease and within different microniches of the nasopharynx. The importance of both serotype‐specific and host tissue‐specific virulence factors during infection and disease has been highlighted by the recent identification of novel virulence factors in this organism coupled with the release of complete genome sequences from two strains. These studies add to the foundation of knowledge of classical S. pneumoniae virulence factors such as polysaccharide capsule and pneumolysin, which have well‐documented roles in pathogenesis
RsmY, a small regulatory RNA, is required in concert with RsmZ for GacA‐dependent expression of biocontrol traits in Pseudomonas fluorescens CHA0
Authors: Valverde Claudio , Heeb Stephan , Keel Christoph , Haas Dieter 
Published: November 2003

SummaryIn the plant‐beneficial soil bacterium and biocontrol model organism Pseudomonas fluorescens CHA0, the GacS/GacA two‐component system upregulates the production of biocontrol factors, i.e. antifungal secondary metabolites and extracellular enzymes, under conditions of slow, non‐exponential growth. When activated, the GacS/GacA system promotes the transcription of a small regulatory RNA (RsmZ), which sequesters the small RNA‐binding protein RsmA, a translational regulator of genes involved in biocontrol. The gene for a second GacA‐regulated small RNA (RsmY) was detected in silico in various pseudomonads, and was cloned from strain CHA0. RsmY, like RsmZ, contains several characteristic GGA motifs. The rsmY gene was expressed in strain CHA0 as a 118 nt transcript which was most abundant in stationary phase, as revealed by Northern blot and transcriptional fusion analysis. Transcription of rsmY was enhanced by the addition of the strain's own supernatant extract containing a quorum‐sensing signal and was abolished in gacS or gacA mutants. An rsmA mutation led to reduced rsmY expression, via a gacA‐independent mechanism. Overexpression of rsmY restored the expression of target genes (hcnA, aprA) to gacS or gacA mutants. Whereas mutants deleted for either the rsmY or the rsmZ structural gene were not significantly altered in the synthesis of extracellular products (hydrogen cyanide, 2,4‐diacetylphloroglucinol, exoprotease), an rsmY rsmZ double mutant was strongly impaired in this production and in its biocontrol properties in a cucumber‐Pythium ultimum microcosm. Mobility shift assays demonstrated that multiple molecules of RsmA bound specifically to RsmY and RsmZ RNAs. In conclusion, two small, untranslated RNAs, RsmY and RsmZ, are key factors that relieve RsmA‐mediated regulation of secondary metabolism and biocontrol traits in the GacS/GacA cascade of strain CHA0.
Response to culture aeration mediated by the nitrate and nitrite sensor NarQ of Escherichia coli K‐12
Authors: Stewart Valley , Chen Li‐Ling , Wu Hui‐chung 
Published: November 2003

SummaryRespiratory enzyme synthesis in enterobacteria is controlled in response to electron acceptor availability. The iron–sulphur protein Fnr and the sensor–regulator proteins ArcB–ArcA control respiratory gene transcription in response to oxygen and quinone pool redox status respectively. The sensor–regulator proteins NarX–NarL and NarQ–NarP control anaerobic respiratory gene expression in response to nitrate and nitrite. Our laboratory recently engineered the lac operon to replace the primary operator O1‐lac with the NarL and NarP protein binding site from the nirB operon. Expression of the lacZ gene from this construct is repressed by nitrate in Nar+ strains. Here, we found that lacZ gene expression was repressed in aerated cultures of narQ+narX null strains. This repression was not observed in narX+narQ+ or narX+narQ null strains. Thus, the NarQ sensor responds to aeration as well as to nitrate and nitrite. The NarX and NarQ sensors are composed of three distinct modules: an amino‐terminal sensory module, a carboxyl‐terminal transmitter module and a central module of unknown function. Experiments with NarX–NarQ hybrid proteins suggest that the NarQ protein central module is necessary for response to aeration. The physiological significance of this additional sensory role for the NarQ sensor remains obscure.
Lsr‐mediated transport and processing of AI‐2 in Salmonella typhimurium
Authors: Taga Michiko E. , Miller Stephen T. , Bassler Bonnie L. 
Published: November 2003

SummaryThe LuxS‐dependent autoinducer AI‐2 is proposed to function in interspecies cell–cell communication in bacteria. In Salmonella typhimurium, AI‐2 is produced and released during exponential growth and is subsequently imported into the bacteria via the Lsr (luxS regulated) ATP binding cassette (ABC) transporter. AI‐2 induces transcription of the lsrACDBFGE operon, the first four genes of which encode the Lsr transport apparatus. In this report, we identify and characterize LsrK, a new protein that is required for the regulation of the lsr operon and the AI‐2 uptake process. LsrK is a kinase that phosphorylates AI‐2 upon entry into the cell. Our data indicate that phosphorylation of AI‐2 results in its sequestration in the cytoplasm. We suggest that phospho‐AI‐2 is the inducer responsible for inactivation of LsrR, the repressor of the lsr operon. We also show that two previously uncharacterized members of the lsr operon, LsrF and LsrG, are necessary for the further processing of phospho‐AI‐2. Transport and processing of AI‐2 could be required for removing the quorum‐sensing signal, conveying the signal to an internal detector and/or scavenging boron.
Polar‐biased localization of the cold stress‐induced RNA helicase, CrhC, in the Cyanobacterium Anabaena sp. strain PCC 7120
Authors: El‐Fahmawi Bassam , Owttrim George W. 
Published: November 2003

SummaryShift of the filamentous cyanobacterium, Anabaena sp. strain PCC 7120, from 30°C to 20°C induces expression of a cold shock response gene encoding the RNA helicase CrhC. Subcellular localization using cellular fractionation and membrane purification indicated that CrhC is localized to the plasma membrane with no evidence of a soluble‐cytoplasmic form. Treatment of spheroplasts with trypsin and membrane fractions with various denaturing agents identified CrhC as an integral membrane protein associated with the cytoplasmic face of the plasma membrane. Immunoelectron microscopy confirmed the plasma membrane association of CrhC. Interestingly, a higher specific labelling was observed at the cell poles on the septa between adjacent cells within cell filaments. On a per cell area basis, CrhC localization to the cell pole was 3.5‐ and> 1000‐fold higher than to the lateral portion of the plasma membrane or cytoplasm respectively. In addition, CrhC also localizes to new cell poles forming within a dividing cell. Polar‐biased localization of the CrhC RNA helicase implies a role in RNA metabolism that is plasma membrane associated and preferentially occurs at the cell poles during cyanobacterial response to cold stress.
Characterization of the pathway for transport of the cytoadherence‐mediating protein, PfEMP1, to the host cell surface in malaria parasite‐infected erythrocytes
Authors: Kriek Neline , Tilley Leann , Horrocks Paul , Pinches Robert , Elford Barry C. , Ferguson David J. P. , Lingelbach Klaus , Newbold Chris I. 
Published: November 2003

SummaryThe Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family of antigenically diverse proteins is expressed on the surface of human erythrocytes infected with the malaria parasite P. falciparum, and mediates cytoadherence to the host vascular endothelium. In this report, we show that export of PfEMP1 is slow and inefficient as it takes several hours to traffic newly synthesized proteins to the erythrocyte membrane. Upon removal by trypsin treatment, the surface‐exposed population of PfEMP1 is not replenished during subsequent culture indicating that there is no cycling of PfEMP1 between the erythrocyte surface and an intracellular compartment. The role of Maurer's clefts as an intermediate sorting compartment in trafficking of PfEMP1 was investigated using immunoelectron microscopy and proteolytic digestion of streptolysin O‐permeabilized parasitized erythrocytes. We show that PfEMP1 is inserted into the Maurer's cleft membrane with the C‐terminal domain exposed to the erythrocyte cytoplasm, whereas the N‐terminal domain is buried inside the cleft. Transfer of PfEMP1 to the erythrocyte surface appears to involve electron‐lucent extensions of the Maurer's clefts. Thus, we have delineated some important aspects of the unusual trafficking mechanism for delivery of this critical parasite virulence factor to the erythrocyte surface.
Reactive oxygen species generated by microbial NADPH oxidase NoxA regulate sexual development in Aspergillus nidulans
Authors: Lara‐Ortíz Teresa , Riveros‐Rosas Héctor , Aguirre Jesús 
Published: November 2003

SummaryNADPH oxidases (Nox) have been characterized as higher eukaryotic enzymes used deliberately to produce reactive oxygen species (ROS). The recent discovery of new functional members of the Nox family in plants and animals has led to the recognition of the increasing importance of ROS as signals involved in regulation of diverse cellular processes such as defence, growth and signalling. Here, we address the role of NADPH oxidase‐generated ROS in the biology of the filamentous fungus Aspergillus nidulans. We characterize the noxA gene and show that it encodes a member of a novel NADPH oxidase subfamily ubiquitous in lower eukaryotes. Deletion of noxA specifically blocks differentiation of sexual fruit bodies (cleistothecia), without affecting hyphal growth or asexual development. Accordingly, the noxA gene is induced during sexual development, peaking at the time of cleistothecia differentiation and in parallel with the hülle cell‐associated catalase peroxidase gene cpeA. This expression pattern is not dependent on transcription factors SteA and StuA, which are essential for cleistothecia formation. In contrast, noxA‐dependent premature sexual development correlates with noxA derepression in ΔsakA null mutants, connecting stress MAPK signalling to the regulated production of ROS. Using a nitroblue tetrazolium (NBT) assay to detect superoxide, we found that hülle cells and cleistothecia initials produce superoxide in a process inhibited by NADPH oxidase inhibitor DPI and markedly reduced in ΔnoxA mutants. Furthermore, using H2DCFDA, we detected that H2O2 and possibly other ROS are generated in a NoxA‐dependent fashion, mainly in the external walls from cleistothecia initials. The essential role of NoxA‐generated ROS in A. nidulans sexual differentiation and the presence of one or two noxA homologues in all analysed filamentous fungi suggest that NADPH oxidase‐generated ROS play important roles in fungal physiology and differentiation.
Partial characterization of a bipartite begomovirus infecting yellow passion flower in Brazil
Authors: Novaes Q. S. , Freitas‐Astua J. , Yuki V. A. , Kitajima E. W. , Camargo L. E. A. , Rezende J. A. M. 
Published: November 2003

During the spring of 2001, approximately 10 000 yellow passion flower plants, from two orchards in the county of Livramento de Nossa Senhora, Bahia State, Brazil, exhibited intense yellow mosaic symptoms and drastic reduction of the leaf lamina and plant development. A large population of whiteflies (Bemisia tabaci) was also found colonizing the plants. All field samples collected tested positive for Passion fruit woodiness virus in DAS‐ELISA. Five out of 20 passion flower plants inoculated with adult whiteflies collected from diseased plants in the field developed symptoms 20–30 days after inoculation. Two of these plants gave a positive reaction in TAS‐ELISA using antiserum against a begomovirus. Degenerated PCR primers amplified viral DNA fragments from the DNA‐A and DNA‐B components of a begomovirus infecting these plants. The fragment corresponding to the core region of the coat protein (DNA‐A) was cloned and sequenced. A phylogenetic analysis placed this begomovirus isolated from passion flower in the same clade of the New World begomoviruses as several other species from Brazil. Based on the symptoms induced by this virus alone, the disease was tentatively named passion flower little leaf mosaic.
Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditions
Authors: Chen L. Y. , Price T. V. , Park‐Ng Z. 
Published: November 2003

This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage (Brassica pekinensis). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r2 of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants.
Predicting effective doses for the joint action of two fungicide applications
Authors: Paveley N. D. , Thomas J. M. , Vaughan T. B. , Havis N. D. , Jones D. R. 
Published: November 2003

A function was derived to predict fungicide efficacy when more than one application of a single active ingredient is made to a crop, given parameters describing the dose–response curves of the component single‐spray applications. In the function, a second application is considered to act on that proportion of the total pathogen population which was uncontrollable at the time of the first application (represented by the lower asymptote of the dose–response curve for the first treatment), plus any additional part of the population which survived the first application as a result of a finite dose being applied. Data to estimate the single‐spray dose–response curve parameters and validate predictions of two‐spray programme efficacy were obtained from separate subsets of treatments in four field experiments. A systemic fungicide spray was applied to wheat at a range of doses, at one or both of two times (t1andt2), in all dose combinations. Observed values of the area under the disease progress curve (AUDPC) for septoria leaf blotch (Mycosphaerella graminicola) were used to construct response surfaces of dose att1by dose att2for each culm leaf layer. Parameters were estimated from single‐spray and zero‐dose treatment data only. The model predicted a high proportion (R2 = 71–95%) of the variation in efficacy of the two‐spray programmes. AUDPC isobols showed that the dose required att2was inversely related to the dose att1, but the slope of the relationship varied with the relative timings oft1andt2in relation to culm leaf emergence. Isobols were curved, so the effective dose – the total dose required to achieve a given level of disease suppression – was lower when administered as two applications.
Phoma–Didymella complex on hybrid arctic bramble with wilting symptoms
Authors: Lindqvist‐Kreuze H. , Hellqvist S. , Koponen H. , Valkonen J. P. T. 
Published: November 2003

Pycnidia containing conidia characteristic of Phoma spp. and pseudothecia containing ascospores characteristic of Didymella applanata were isolated from edges of expanding stem lesions and dead stems of wilted cultivated hybrid arctic bramble plants (Rubus arcticus nothossp. stellarcticus) in Sweden in 1998 and 1999. The fungi were morphologically similar when grown on culture media, but some differences in growth rate were observed. They were also similar to the reference isolates of D. applanata (anamorph Phoma argillacea). However, they were different from an isolate of Phoma sp. (HPP 38) isolated from cultivated arctic bramble (R. arcticus ssp. arcticus) in Finland in 1980, and from reference isolates of Phoma glomerata isolated from other hosts. Multivariate analysis of growth rate data and conidial dimensions measured in vitro indicated that the fungi isolated from hybrid arctic bramble in Sweden were not distinguishable from D. applanata, but were clearly distinct from P. glomerata and P. exigua. Furthermore, they had identical ITS1 and ITS2 sequences, and were placed in a phylogenetic clade very closely related to the clade that contained isolates of D. applanata isolated from raspberry (Rubus idaeus). In contrast, isolate HPP 38 from Finland was placed in a clade with P. exigua. These data indicate that the Swedish isolates infecting arctic bramble belong to a strain of D. applanata that differs from the isolate infecting raspberry only by two common nucleotide substitutions in ITS2. Fungi of the Phoma–Didymella complex on wild and cultivated arctic bramble (a total of 291 plants showing symptoms sampled from 37 sites) were detected by a PCR‐based assay and found to be common in northern Sweden, but rare, albeit widely distributed, in Finland.
Ovary colonization by Claviceps africana is related to ergot resistance in male‐sterile sorghum lines
Authors: Komolong B. , Chakraborty S. , Ryley M. , Yates D. 
Published: November 2003

Ergot, caused by Claviceps africana, has emerged as a serious threat to sorghum hybrid seed production worldwide. In the absence of gene‐for‐gene‐based qualitative resistance in commercial cultivars, varieties with high pollen production that can escape ergot infection are preferred. Recent demonstration of differences in ergot susceptibility among male‐sterile lines has indicated the presence of partial resistance. Using chitin‐specific fluorescin‐isothiocyanate‐conjugated wheat germ agglutin and callose‐specific aniline blue, this study investigated the process of sorghum ovary colonization by C. africana. Conidia germinated within 24 h after inoculation (a.i.); the pathogen was established in the ovary by 79 h a.i., and at least half of the ovary was converted into sphacelial tissue by 120 h a.i. Changes in fungal cell wall chitin content and strategic callose deposition in the host tissue were associated with penetration and invasion of the ovary. The rate of ovary colonization differed in three male‐sterile lines that also differed in ergot susceptibility. This work demonstrates a possible histological basis for partial resistance in male‐sterile sorghum lines that could lay the foundation for variety improvement through further breeding and selection.