bluuebunny/crossref_metadata_2025_split huggingface dataset:
Serum opacity factor promotes group A streptococcal epithelial cell invasion and virulence
Authors: Timmer Anjuli M. , Kristian Sascha A. , Datta Vivekanand , Jeng Arthur , Gillen Christine M. , Walker Mark J. , Beall Bernard , Nizet Victor 
Published: August 2006

SummarySerum opacity factor (SOF) is a bifunctional cell surface protein expressed by 40–50% of group A streptococcal (GAS) strains comprised of a C‐terminal domain that binds fibronectin and an N‐terminal domain that mediates opacification of mammalian sera. The sof gene was recently discovered to be cotranscribed in a two‐gene operon with a gene encoding another fibronectin‐binding protein, sfbX. We compared the ability of a SOF(+) wild‐type serotype M49 GAS strain and isogenic mutants lacking SOF or SfbX to invade cultured HEp‐2 human pharyngeal epithelial cells. Elimination of SOF led to a significant decrease in HEp‐2 intracellular invasion while loss of SfbX had minimal effect. The hypoinvasive phenotype of the SOF(–) mutant could be restored upon complementation with the sof gene on a plasmid vector, and heterologous expression of sof49 in M1 GAS or Lactococcus lactis conferred marked increases in HEp‐2 cell invasion. Studies using a mutant sof49 gene lacking the fibronectin‐binding domain indicated that the N‐terminal opacification domain of SOF contributes to HEp‐2 invasion independent of the C‐terminal fibronectin binding domain, findings corroborated by observations that a purified SOF N‐terminal peptide could promote latex bead adherence to HEp‐2 cells and inhibit GAS invasion of HEp‐2 cells in a dose‐dependent manner. Finally, the first in vivo studies to employ a single gene allelic replacement mutant of SOF demonstrate that this protein contributes to GAS virulence in a murine model of necrotizing skin infection.
Regulation of tylosin biosynthesis involving ‘SARP‐helper’ activity
Authors: Bate Neil , Bignell Dawn R. D. , Cundliffe Eric 
Published: August 2006

SummaryTylosin production in Streptomyces fradiae is regulated via interplay between a repressor, TylQ, and an activator of the SARP family, TylS, during regulation of tylR. The latter encodes the pathway‐specific activator of the tylosin‐biosynthetic (tyl) genes. Also controlled by TylS is a hitherto unassigned gene, tylU, whose product is shown here to be important for tylosin production. Thus, targeted disruption of tylU reduced tylosin yields by about 80% and bioconversion analysis with the resultant strain revealed defects in both polyketide metabolism and deoxyhexose biosynthesis. Such defects were completely eliminated by engineered overexpression of tylR (but not tylS) and Western analysis revealed significantly reduced levels of TylR in the tylU‐disrupted strain. These results are consistent with a model in which TylS and TylU act in concert to facilitate expression of tylR, for which TylU (but not TylS) is nonessential. Activator proteins of the SARP family, such as TylS, are widespread among Streptomyces spp. and are important regulators of antibiotic production. Their action has been widely studied with no prior indication of associated ‘helper’ activity, the prevalence of which now remains to be established.
The type III effector repertoire of Pseudomonas syringae pv. syringae B728a and its role in survival and disease on host and non‐host plants
Authors: Vinatzer Boris A. , Teitzel Gail M. , Lee Min‐Woo , Jelenska Joanna , Hotton Sara , Fairfax Keke , Jenrette Jenny , Greenberg Jean T. 
Published: August 2006

SummaryThe bacterial plant pathogen Pseudomonas syringae injects a large repertoire of effector proteins into plant cells using a type III secretion apparatus. Effectors can trigger or suppress defences in a host‐dependent fashion. Host defences are often accompanied by programmed cell death, while interference with defences is sometimes associated with cell death suppression. We previously predicted the effector repertoire of the sequenced bean pathogen P. syringae pv. syringae (Psy) B728a using bioinformatics. Here we show that PsyB728a is also pathogenic on the model plant species Nicotiana benthamiana (tobacco). We confirm our effector predictions and clone the nearly complete PsyB728a effector repertoire. We find effectors to have different cell death‐modulating activities and distinct roles during the infection of the susceptible bean and tobacco hosts. Unexpectedly, we do not find a strict correlation between cell death‐eliciting and defence‐eliciting activity and between cell death‐suppressing activity and defence‐interfering activity. Furthermore, we find several effectors with quantitative avirulence activities on their susceptible hosts, but with growth‐promoting effects on Arabidopsis thaliana, a species on which PsyB728a does not cause disease. We conclude that P. syringae strains may have evolved large effector repertoires to extend their host ranges or increase their survival on various unrelated plant species.
Succinic semialdehyde couples stress response to quorum‐sensing signal decay in Agrobacterium tumefaciens
Authors: Wang Chao , Zhang Hai‐Bao , Wang Lian‐Hui , Zhang Lian‐Hui 
Published: August 2006

SummaryQuorum sensing (QS) signal decay in Agrobacterium tumefaciens occurs in response to starvation or host signals. We have demonstrated that the γ‐aminobutyric acid (GABA) shunt metabolite links stress response to QS signal decay. Mutation of the aldH gene encoding a succinic semialdehyde dehydrogenase (SSADH) that converts succinic semialdehyde (SSA) to succinic acid results in early expression of the signal degrading enzyme, AttM. Exogenous addition of SSA or its precursor GABA induces AttM expression and abolishes Ti plasmid conjugative transfer. SSA acts by binding to the repressor AttJ that regulates the attKLM operon. attK encodes another SSADH. The stress alarmone ppGpp and SSA modulates separately the expression of the two SSADH enzymes, which might control the intracellular SSA level and hence to switch on/off the QS signal decay system in response to environmental changes. These findings document for the first time a sophisticated signalling mechanism of the widely conserved GABA degradation pathway in prokaryotes.
Spatial and temporal organization of the Bacillus subtilis replication cycle
Authors: Berkmen Melanie B. , Grossman Alan D. 
Published: August 2006

SummaryDNA replication occurs at discrete sites in the cell. To gain insight into the spatial and temporal organization of the Bacillus subtilis replication cycle, we simultaneously visualized replication origins and the replication machinery (replisomes) inside live cells. We found that the origin of replication is positioned near midcell prior to replication. After initiation, the replisome colocalizes with the origin, confirming that replication initiates near midcell. The replisome remains near midcell after duplicated origins separate. Artificially mispositioning the origin region leads to mislocalization of the replisome indicating that the location of the origin at the time of initiation establishes the position of the replisome. Time‐lapse microscopy revealed that a single replisome focus reversibly splits into two closely spaced foci every few seconds in many cells, including cells that recently initiated replication. Thus, sister replication forks are likely not intimately associated with each other throughout the replication cycle. Fork dynamics persisted when replication elongation was halted, and is thus independent of the relative movement of DNA through the replisome. Our results provide new insights into how the replisome is positioned in the cell and refine our current understanding of the spatial and temporal events of the B. subtilis replication cycle.
Heterozygosity and functional allelic variation in theCandida albicansefflux pump genesCDR1andCDR2
Authors: Holmes Ann R. , Tsao Sarah , Ong Soo‐Wee , Lamping Erwin , Niimi Kyoko , Monk Brian C. , Niimi Masakazu , Kaneko Aki , Holland Barbara R. , Schmid Jan , Cannon Richard D. 
Published: August 2006

SummaryElevated expression of the plasma membrane drug efflux pump proteins Cdr1p and Cdr2p was shown to accompany decreased azole susceptibility inCandida albicansclinical isolates. DNA sequence analysis revealed extensive allelic heterozygosity, particularly ofCDR2. Cdr2p alleles showed different abilities to transport azoles when individually expressed inSaccharomyces cerevisiae. Loss of heterozygosity, however, did not accompany decreased azole sensitivity in isogenic clinical isolates. Two adjacent non‐synonymous single nucleotide polymorphisms (NS‐SNPs), G1473A and I1474V in the putative transmembrane (TM) helix 12 ofCDR2,were found to be present in six strains including two isogenic pairs. Site‐directed mutagenesis showed that the TM‐12 NS‐SNPs, and principally the G1473A NS‐SNP, contributed to functional differences between the proteins encoded by the two Cdr2p alleles in a single strain. Allele‐specific PCR revealed that both alleles were equally frequent among 69 clinical isolates and that the majority of isolates (81%) were heterozygous at the G1473A/I1474V locus, a significant (P < 0.001) deviation from the Hardy–Weinberg equilibrium. Phylogenetic analysis by maximum likelihood (Paml) identified 33 codons inCDR2in which amino acid allelic changes showed a high probability of being selectively advantageous. In contrast, all codons inCDR1were under purifying selection. Collectively, these results indicate that possession of two functionally differentCDR2alleles in individual strains may confer a selective advantage, but that this is not necessarily due to azole resistance.
Evidence that Plasmodium falciparum chromosome end clusters are cross‐linked by protein and are the sites of both virulence gene silencing and activation
Authors: Marty Allison J. , Thompson Jennifer K. , Duffy Michael F. , Voss Till S. , Cowman Alan F. , Crabb Brendan S. 
Published: August 2006

SummaryThe malaria parasite Plasmodium falciparum undergoes antigenic variation through allelic exclusion and variant expression of surface proteins encoded by the var gene family. Regulation of var genes is under epigenetic control and involves reversible silencing and activation that requires the physical repositioning of a var locus into a transcriptionally permissive zone of the nuclear periphery. P. falciparum chromosome ends appear to aggregate into large perinuclear clusters which house both subtelomeric and chromosome central var genes. In this study we further define the composition of telomeric clusters using fluorescent in situ hybridization, and provide evidence that chromosome end clusters are formed by cross‐linking protein. In addition, we demonstrate that a subtelomeric reporter gene and a var gene remain within clusters regardless of their transcriptional status. Our findings support a model whereby a highly localized structure dedicated to the activation of a single var gene can be housed within a gene dense chromosome end cluster that is otherwise transcriptionally silent.
Al–Fe interactions and growth enhancement in Melastoma malabathricum and Miscanthus sinensis dominating acid sulphate soils
Authors: WATANABE TOSHIHIRO , JANSEN STEVEN , OSAKI MITSURU 
Published: August 2006

ABSTRACTPlants growing in acid sulphate soils are subject to high levels of Al availability, which may have effects on the growth and distribution of these species. Although Fe availability is also high in acid sulphate soils, little is known about the effect of Fe on the growth of native plants in these soils. Two species dominating this soil type in Asia, viz. Melastoma malabathricum and Miscanthus sinensis were grown hydroponically in a nutrient solution with different concentrations of Al and Fe. Melastoma malabathricum is found to be sensitive to Fe (40 and 100 µm). Application of 500 µm Al, however, completely ameliorates Fe toxicity and is associated with a decrease of Fe concentration in shoots and roots. The primary reason for the Al‐induced growth enhancement of M. malabathricum is considered to be the Al‐induced reduction of toxic Fe accumulation in roots and shoots. Therefore, Al is nearly essential for M. malabathricum when growing in acid sulphate soils. In contrast, application of both Fe and Al does not reduce the growth of M. sinensis, and Al application does not result in lower shoot concentrations of Fe, suggesting that this grass species has developed different mechanisms for adaptation to acid sulphate soils.
The impact of coral bleaching on the pigment profile of the symbiotic alga, Symbiodinium
Authors: VENN ALEXANDER A. , WILSON MICHAEL A. , TRAPIDO‐ROSENTHAL HENRY G. , KEELY BRENDAN J. , DOUGLAS ANGELA E. 
Published: August 2006

ABSTRACTBleaching of corals by loss of symbiotic dinoflagellate algae and/or photosynthetic pigments is commonly triggered by elevated temperatures coupled with high irradiance, and is a first‐order threat to coral reef communities. In this study, a high‐resolution high‐performance liquid chromatography method integrated with mass spectrometry was applied to obtain the first definitive identification of chlorophyll and carotenoid pigments of three clades of symbiotic dinoflagellate algae (Symbiodinium) in corals, and their response to experimentally elevated temperature and irradiance. The carotenoids peridinin, dinoxanthin, diadinoxanthin (Dn), diatoxanthin (Dt) and β‐carotene were detected, together with chlorophylls a and c2, and phaeophytin a, in all three algal clades in unstressed corals. On exposure to elevated temperature and irradiance, three coral species (Montastrea franksi and Favia fragum with clade B algae, and Montastrea cavernosa with clade C) bleached by loss of 50–80% of their algal cells, with no significant impact to chlorophyll a or c2, or peridinin in retained algal cells. One species (Agaricia sp. with clade C) showed no significant reduction in algal cells at elevated temperature and irradiance, but lost substantial amounts of chlorophyll a and carotenoid pigments, presumably through photo‐oxidative processes. Two coral species (Porites astreoides and Porites porites both bearing clade A algae) did not bleach. The impact of elevated temperature and irradiance on the levels of the photoprotective xanthophylls (Dn + Dt) and β‐carotene varied among the corals, both in pool size and xanthophyll cycling, and was not correlated to coral bleaching resistance.
Drought stress response in wheat: physiological and molecular analysis of resistant and sensitive genotypes
Authors: RAMPINO PATRIZIA , PATALEO STEFANO , GERARDI CARMELA , MITA GIOVANNI , PERROTTA CARLA 
Published: August 2006

ABSTRACTWater deficit is a severe environmental stress and the major constraint on plant productivity with an evident effect on plant growth. The aim of this work was to study Triticum and Aegilops seedlings differing in their response to drought stress at the physiological and molecular levels. The identification of resistant and sensitive genotypes was firstly based on the relative water content (RWC) measurement. Further characterization of genotypes contrasting in their response to water stress was performed at the physiological level by determination of RWC, water loss rate (WLR) and free proline content after different hours of dehydration. Modification in the expression level of five dehydrin (DHN) genes was also analysed by reverse transcription–polymerase chain reaction (RT‐PCR). Five cDNAs coding for different DHNs were identified and characterized. These genes are not expressed in the well‐watered plants, but only in the stressed plants. Four of these cDNAs are related to novel DHN sequences. The results obtained clearly indicate a relation between the expression of these genes and tissue water content. In particular, in the resistant genotypes the expression of DHN genes is initiated even though tissue hydration levels are still high, indicating also in wheat the involvement of these proteins in water retention.
Phototropin involvement in the expression of genes encoding chlorophyll and carotenoid biosynthesis enzymes and LHC apoproteins in Chlamydomonas reinhardtii
Authors: Im Chung‐Soon , Eberhard Stephan , Huang Kaiyao , Beck Christoph F. , Grossman Arthur R. 
Published: August 2006

SummaryPhototropin (PHOT) is a photoreceptor involved in a variety of blue‐light‐elicited physiological processes including phototropism, chloroplast movement and stomatal opening in plants. The work presented here tests whether PHOT is involved in expression of light‐regulated genes in Chlamydomonas reinhardtii. When C. reinhardtii was transferred from the dark to very low‐fluence rate white light, there was a substantial increase in the level of transcripts encoding glutamate‐1‐semialdehyde aminotransferase (GSAT), phytoene desaturase (PDS) and light‐harvesting polypeptides (e.g. LHCBM6). Increased levels of these transcripts were also elicited by low‐intensity blue light, and this blue‐light stimulation was suppressed in three different RNAi strains that synthesize low levels of PHOT. The levels of GSAT and LHCBM6 transcripts also increased following exposure of algal cells to low‐intensity red light (RL). The red‐light‐dependent increase in transcript abundance was not affected by the electron transport inhibitor 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea, implying that the influence of RL on transcript accumulation was not controlled by cytoplasmic redox conditions, and that a red‐light photoreceptor(s) may be involved in regulating the levels of transcripts from specific photosynthesis‐related genes in C. reinhardtii. Interestingly, elevated GSAT and LHCBM6 transcript levels in RL were significantly reduced in the PHOT RNAi strains, which raises the possibility of co‐action between blue and RL signaling pathways. Microarray experiments indicated that the levels of several transcripts for photosystem (PS) I and II polypeptides were also modulated by PHOT. These data suggest that, in C. reinhardtii, (i) PHOT is involved in blue‐light‐mediated changes in transcript accumulation, (ii) synchronization of the synthesis of chlorophylls (Chl), carotenoids, Chl‐binding proteins and other components of the photosynthetic apparatus is achieved, at least in part, through PHOT‐mediated signaling, and (iii) a red‐light photoreceptor can also influence levels of certain transcripts associated with photosynthetic function, although its action requires normal levels of PHOT.
Biosynthesis and secretion of mugineic acid family phytosiderophores in zinc‐deficient barley
Authors: Suzuki Motofumi , Takahashi Michiko , Tsukamoto Takashi , Watanabe Satoshi , Matsuhashi Shinpei , Yazaki Junshi , Kishimoto Naoki , Kikuchi Shoshi , Nakanishi Hiromi , Mori Satoshi , Nishizawa Naoko K. 
Published: August 2006

SummaryMugineic acid family phytosiderophores (MAs) are metal chelators that are produced in graminaceous plants in response to iron (Fe) deficiency, but current evidence regarding secretion of MAs during zinc (Zn) deficiency is contradictory. Our studies using HPLC analysis showed that Zn deficiency induces the synthesis and secretion of MAs in barley plants. The levels of the HvNAS1, HvNAAT‐A, HvNAAT‐B, HvIDS2 and HvIDS3 transcripts, which encode the enzymes involved in the synthesis of MAs, were increased in Zn‐deficient roots. Studies of the genes involved in the methionine cycle using microarray analysis showed that the transcripts of these genes were increased in both Zn‐deficient and Fe‐deficient barley roots, probably allowing the plant to meet its demand for methionine, a precursor in the synthesis of MAs. In addition, HvNAAT‐B transcripts were detected in Zn‐deficient shoots, but not in those that were deficient in Fe. Increased synthesis of MAs in Zn‐deficient barley was not due to a deficiency of Fe, because Zn‐deficient barley accumulated more Fe than did the control plants, ferritin transcripts were increased in Zn‐deficient plants, and Zn deficiency promoted Fe transport from root to shoot. Moreover, analysis using the positron‐emitting tracer imaging system (PETIS) confirmed that more 62Zn(II)‐MAs than 62Zn2+ were absorbed by the roots of Zn‐deficient barley plants. These data suggest that the increased biosynthesis and secretion of MAs arising from a shortage of Zn are not due to an induced Fe deficiency, and that secreted MAs are effective in absorbing Zn from the soil.
Multi‐site genetic modulation of monolignol biosynthesis suggests new routes for formation of syringyl lignin and wall‐bound ferulic acid in alfalfa (Medicago sativa L.)
Authors: Chen Fang , Srinivasa Reddy Marry S. , Temple Stephen , Jackson Lisa , Shadle Gail , Dixon Richard A. 
Published: August 2006

SummaryGenes encoding seven enzymes of the monolignol pathway were independently downregulated in alfalfa (Medicago sativa) using antisense and/or RNA interference. In each case, total flux into lignin was reduced, with the largest effects arising from the downregulation of earlier enzymes in the pathway. The downregulation of l‐phenylalanine ammonia‐lyase, 4‐coumarate 3‐hydroxylase, hydroxycinnamoyl CoA quinate/shikimate hydroxycinnamoyl transferase, ferulate 5‐hydroxylase or caffeic acid 3‐O‐methyltransferase resulted in compositional changes in lignin and wall‐bound hydroxycinnamic acids consistent with the current models of the monolignol pathway. However, downregulating caffeoyl CoA 3‐O‐methyltransferase neither reduced syringyl (S) lignin units nor wall‐bound ferulate, inconsistent with a role for this enzyme in 3‐O‐methylation ofS monolignol precursors and hydroxycinnamic acids. Paradoxically, lignin composition differed in plants downregulated in either cinnamate 4‐hydroxylase or phenylalanine ammonia‐lyase. No changes in the levels of acylated flavonoids were observed in the various transgenic lines. The current model for monolignol and ferulate biosynthesis appears to be an over‐simplification, at least in alfalfa, and additional enzymes may be needed for the 3‐O‐methylation reactions of S lignin and ferulate biosynthesis.
DamID, a new tool for studying plant chromatin profiling in vivo, and its use to identify putative LHP1 target loci
Authors: Germann Sophie , Juul‐Jensen Trine , Letarnec Bruno , Gaudin Valérie 
Published: August 2006

SummaryWe show here that the in vivo methylation‐based tagging technique DamID (DNA adenine methyltransferase identification) can be used for studies of DNA–protein interactions or chromatin profiling in plants. We have demonstrated the feasibility, reproducibility and sensitivity of the method in Arabidopsis thaliana, using the well‐known yeast GAL4 transcription factor, for which DNA‐binding sites (UASG) were introduced into the plant genome. We monitored the methylation resulting from the activity of DNA adenine methyltransferase fused to the protein of interest, by combining digestion with methylation‐sensitive restriction enzymes and quantitative PCR. We then used DamID to identify genomic targets of LHP1, a protein mostly associated with euchromatin. We showed that LHP1 was targeted to the promoter and transcribed regions of four genes: AG, AP3, FT and PI. Our data also demonstrate that LHP1, like its animal homologues, has a high binding affinity for A/T‐rich regions, binding particularly strongly to the large regulatory introns of AG and PI. We identified three major characteristics of LHP1 binding, highlighting the similarities between plant LHP1 and animal HP1 proteins.