bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial pattern of chloroplast DNA variation of Cyclobalanopsis glauca in Taiwan and East Asia
Authors: Huang Sophie S. F. , Hwang Shih‐Ying , Lin Tsan‐Piao 
Published: March 2003

AbstractThis study examined the spatial pattern of chloroplast DNA (cpDNA) variation in Cyclobalanopsis glauca (Thunb. ex Murray) Oerst. (Fagaceae) in 140 trees from Taiwan (25 populations), Japan (three), Ryukyus (two), Hong Kong (one) and Mainland China (one). By sequencing three cpDNA intergenic spacer fragments using universal primers (trnT‐trnL, trnV‐trnM, including the trnV intron, and petG‐trnP), we found a total of 1980 bp and 15 polymorphic sites. Among them, 12 sites were caused by point mutation, and three resulted from insertion. This gives rise to a total of 13 cpDNA haplotypes. The level of differentiation among the populations studied is relatively high (GST = 0.612). Two ancestral haplotypes (A and B) are distributed widely in East Asia. Interestingly, all the derived cpDNA variations are found only in Taiwan but not in other areas. The Central Mountain Ridge (CMR) of Taiwan creates an unsurpassed barrier to the east–west gene flow of C. glauca. Among the populations on the west of CMR, only three separated populations, Yangmingshan, Wushe and Chinshuiying, have high haplotype diversity, each consisting of sister haplotypes all mutated from the same ancestral haplotype. Thus, they have probably originated from de novo mutation after the last glaciation. This inference agrees with the observation that no spatial autocorrelation existed on the west side. Two unrelated dominant lineages on the east of the CMR (haplotypes D and F) showed significant spatial genetic structure. Estimate of NST – GST was –0.090 and differed significantly from zero. Thus at the local scale, the phylogeographical component of the genetic structure is significant on the east of the CMR. Accompanied by published palynological records of the last glaciation, this study suggests the possibility that these two types were colonized northward from the southeastern part of Taiwan. ‘Star‐like’ genealogy is characterized, with all the haplotypes coalescing rapidly and as a general outcome of population expansion (Page & Holmes 1998). A neutrality test also suggested a demographic expansion recovered from a bottleneck. We therefore inferred that the southeastern part of Taiwan might be a potential refugium for C. glauca.
Does natural selection promote population divergence? A comparative analysis of population structure using amplified fragment length polymorphism markers and quantitative traits
Authors: Steinger T. , Haldimann P. , Leiss K. A. , Müller‐Schärer H. 
Published: March 2003

AbstractDivergent natural selection is considered an important force in plant evolution leading to phenotypic differentiation between populations exploiting different environments. Extending an earlier greenhouse study of population differentiation in the selfing annual plantSenecio vulgaris, we estimated the degree of population divergence in several quantitative traits related to growth and life history and compared these estimates with those based on presumably neutral molecular markers (amplified fragment length polymorphisms; AFLPs). This approach allowed us to disentangle the effects of divergent selection from that of other evolutionary forces (e.g. genetic drift). Five populations were examined from each of two habitat types (ruderal and agricultural habitats). We found a high proportion of total genetic variance to be among populations, both for AFLP markers (φST = 0.49) and for quantitative traits (range ofQST: 0.26–0.77). There was a strong correlation between molecular and quantitative genetic differentiation between pairs of populations (Mantel'sr = 0.59). However, estimates of population differentiation in several quantitative traits exceeded the neutral expectation (estimated from AFLP data), suggesting that divergent selection contributed to phenotypic differentiation, especially between populations from ruderal and agricultural habitats. Estimates of within‐population variation in AFLP markers and quantitative genetic were poorly correlated, indicating that molecular marker data may be of limited value to predict the evolutionary potential of populations ofS. vulgaris.
Phylogeny, paraphyly and ecological adaptation of the colour and pattern in the Anolis roquet complex on Martinique
Authors: Thorpe R. S. , Stenson A. G. 
Published: March 2003

AbstractMartinique is an environmentally heterogeneous island with a complex geological history. It is occupied by a solitary anole, Anolis roquet, showing marked geographical variation in colour and other features. Phylogenetic analysis of a segment (1 kb) of the mitochondrial cytochrome b gene across the Anolis roquet series in the southern Lesser Antilles and at 63 localities of Anolis roquet in Martinique indicate that A. roquet is paraphyletic as A. extremus (Barbados) is nested within the Martinique populations. Moreover, divergent phylogenetic lineages exist within Martinique (max. 10.6% uncorrected pairwise), and these lineages are closely associated with the geological history of this complex island. However, objective quantification of the spectroradiometric analysis of hue by delta analysis, together with analysis of the colour pattern, indicate that they are primarily determined by adaptation to environmental conditions, irrespective of these phylogenetic lineages. There is remarkable convergence in hue and pattern in both extreme xeric (dark chevrons on a dull, generally grey/brown, background), and montane conditions (black reticulation and non‐UV white spots on a bright, saturated green background). Moreover, parallel trends occur between Martinique and other Lesser Antillean anoles, which further argues for adaptation (increase in green saturation in montane areas and higher levels of UV on the dewlap of some Atlantic forms). As an exception, there are two specific situations where anoles from different lineages look different. These are (i) in the low‐altitude regions of the northwest where the northwestern and central lineages make contact, and (ii) in the far south of the island where the southern and central lineages meet.
Dispersal barriers and isolation among deep‐sea mussel populations (Mytilidae: Bathymodiolus) from eastern Pacific hydrothermal vents
Authors: Won Y. , Young C. R. , Lutz R. A. , Vrijenhoek R. C. 
Published: March 2003

AbstractDeep‐sea hydrothermal vent species are widely dispersed among habitat islands found along the global mid‐ocean ridge system. We examine factors that affect population structure, gene flow and isolation in vent‐endemic mussels of the genus Bathymodiolus from the eastern Pacific Ocean. Mussels were sampled from localities including the Galapagos Rift (GAR, 0°48′ N; 86°10′ W) and the East Pacific Rise (EPR, 13° N to 32° S latitude) across a maximum distance of 4900 km. The sampled range crossed a series of topographical features that interrupt linear aspects of the ridge system, and it encompassed regions of strong cross‐axis currents that could impede along‐axis dispersal of mussel larvae. Examinations of mitochondrial DNA sequences and allozyme variation revealed significant barriers to gene flow along the ridge axis. All populations from the GAR and EPR from 13° N to 11° S were homogeneous genetically and appeared to experience unimpeded high levels of interpopulational gene flow. In contrast, mussels from north and south of the Easter Microplate were highly divergent (4.4%), possibly comprising sister‐species that diverged after formation of the microplate ≈ 4.5 Ma. Strong cross‐axis currents associated with inflated bathymetry of the microplate region may reinforce isolation across this region.
Large extent of mitochondrial DNA transfer fromOreochromis aureustoO. niloticusin West Africa
Authors: Rognon X. , Guyomard R. 
Published: March 2003

AbstractIntrogressive hybridization has an important evolutionary significance in terms of gene diversity and speciation. Among the major groups of vertebrates, fish show a strong propensity to hybridize. In order to highlight the possible occurrence of gene flow between two tilapia species,Oreochromis niloticusandO. aureus, a comparison of allozyme and mitochondrial DNA (mtDNA) polymorphism was performed on sympatric and allopatric populations of these two species. Nuclear data were congruent with the morphological identification ofO. niloticusandO. aureuspopulations. In opposition, the mtDNA analysis resulted in two strictly differentiated groups which did not follow the morphological and nuclear DNA classification. The first group consisted of East AfricanO. niloticuspopulations and the second included all theO. aureuspopulations and the West AfricanO. niloticuspopulations. Moreover, in some cases, the same sequences were detected in both species. These data strongly support a differential introgression of mtDNA fromO. aureustoO. niloticusinvolving all the West African area. This work points out the risk of misinterpretation of mtDNA or nuclear DNA data when only one single class of marker is used.
Paternity success and the direction of sexual selection in a field population of a semelparous marsupial, Antechinus agilis
Authors: Kraaijeveld‐Smit F. J. L. , Ward S. J. , Temple‐Smith P. D. 
Published: March 2003

Abstract Antechinus agilis is a small sexually size dimorphic marsupial with a brief annual mating period of 2–3 weeks. All males die after this period, and females give birth to up to 10 young. Mating is thought to be promiscuous, however, there is no field data to confirm this. Using microsatellites, we investigated paternity patterns over two seasons in a wild population. Male weight was significantly positively related to the number of females fertilized and with the number of offspring sired, in both years. Furthermore, selection gradients indicated selection for larger males. Both results suggest that size dimorphism in A. agilis can be explained by sexual selection for larger males. The proportion of offspring sired within litters, did not relate to male size. Therefore, larger males are more successful through higher mating access, not through their sperm outcompeting that of smaller males. As expected from their known ranging behaviour, the number of offspring within litters left unassigned to a father did not depend on the grid location of the mother. Female size did not differ between successful reproducing and unsuccessful females. However, females that weaned offspring had larger heads than females that did not wean offspring. Males did not ‘prefer’ mating with larger females, nor did assortative mating occur. From our results, the mating system of A. agilis is clearly promiscuous. Selection for larger males occurred in both years, even though in one year the operational sex ratio was highly female biased, suggesting that the potential reproductive rate is a better predictor of the direction of sexual selection in A. agilis.
Genetic variation within and among fragmented populations of lesser prairie‐chickens (Tympanuchus pallidicinctus)
Authors: Van Den Bussche Ronald A. , Hoofer Steven R. , Wiedenfeld David A. , Wolfe Donald H. , Sherrod Steve K. 
Published: March 2003

AbstractAs a result of recurrent droughts and anthropogenic factors, the range of the lesser prairie‐chicken (Tympanuchus pallidicinctus) has contracted by 92% and the population has been reduced by approximately 97% in the past century, resulting in the smallest population size and most restricted geographical distribution of any North American grouse. We examined genetic variation through DNA sequence analysis of 478 base pairs of the mitochondrial genome and by assaying allelic variation at five microsatellite loci from lesser prairie‐chickens collected on 20 leks in western Oklahoma and east‐central New Mexico. Traditional population genetic analyses indicate that lesser prairie‐chickens maintain high levels of genetic variation at both nuclear and mitochondrial loci. Although some genetic structuring among lesser prairie‐chicken leks was detected within Oklahoma and New Mexico for both nuclear and mitochondrial loci, high levels of differentiation were detected between Oklahoma and New Mexico populations. Nested‐clade analysis of mitochondrial haplotypes revealed that both historic and contemporary processes have influenced patterns of haplotype distributions and that historic processes have most likely led to the level of differentiation found between the Oklahoma and New Mexico populations.
A novel NO‐responding regulator controls the reduction of nitric oxide in Ralstonia eutropha
Authors: Pohlmann Anne , Cramm Rainer , Schmelz Karin , Friedrich Bärbel 
Published: March 2003

Ralstonia eutropha H16 mediates the reduction of nitric oxide (NO) to nitrous oxide (N2O) with two isofunctional single component membrane‐bound NO reductases (NorB1 and NorB2). This reaction is integrated into the denitrification pathway that involves the successive reduction of nitrate to dinitrogen. The norB1 gene is co‐transcribed with norA1 from a σ54 (RpoN)‐dependent promoter, located upstream of norA1. With the aid of norA1′–lacZ transcriptional fusions and the generation of regulatory mutants, it was shown that norB1 gene transcription requires a functional rpoN gene and the regulator NorR, a novel member of the NtrC family of response regulators. The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2). Transcription activation by NorR responds to the availability of NO. A nitrite reductase‐deficient mutant that is incapable of producing NO endogenously, showed a 70% decrease of norA1 expression. Addition of the NO‐donating agent sodium nitroprusside caused induction of norA1′–lacZ transcription. Truncation of the N‐terminal receiver domain of NorR1 interrupted the NO signal transduction and led to a constitutive expression of norA1′–lacZ. The results indicate that NorR controls the reductive conversion of NO in R. eutropha. This reaction is not strictly co‐ordinated on the regulatory level with the other nitrogen oxide‐reducing steps of the denitrification chain that are independent of NorR.
Chs1 of Candida albicans is an essential chitin synthase required for synthesis of the septum and for cell integrity
Authors: Munro Carol A. , Winter Ken , Buchan Arlene , Henry Keith , Becker Jeffrey M. , Brown Alistair J. P. , Bulawa Christine E. , Gow Neil A. R. 
Published: March 2003

CaCHS1 of the fungal pathogen Candida albicans encodes an essential chitin synthase that is required for septum formation, viability, cell shape and integrity. The CaCHS1 gene was inactivated by first disrupting one allele using the ura‐blaster protocol, then placing the remaining allele under the control of the maltose‐inducible, glucose‐repressible MRP1 promoter. Under repressing conditions, yeast cell growth continued temporarily, but daughter buds failed to detach from parents, resulting in septumless chains of cells with constrictions defining contiguous compartments. After several generations, a proportion of the distal compartments lysed. The conditional Δchs1 mutant also failed to form primary septa in hyphae; after several generations, growth stopped, and hyphae developed swollen balloon‐like features or lysed at one of a number of sites including the hyphal apex and other locations that would not normally be associated with septum formation. CHS1 therefore synthesizes the septum of both yeast and hyphae and also maintains the integrity of the lateral cell wall. The conditional mutant was avirulent under repressing conditions in an experimental model of systemic infection. Because this gene is essential in vitro and in vivo and is not present in humans, it represents an attractive target for the development of antifungal compounds.
Molecular analysis of the pRA2 partitioning region: ParB autoregulates parAB transcription and forms a nucleoprotein complex with the plasmid partition site, parS
Authors: Kwong Stephen M. , Yeo Chew Chieng , Poh Chit Laa 
Published: March 2003

The partitioning locus (par) of plasmid pRA2 belongs to a recently discovered subgroup of plasmid partitioning systems that are evolutionarily distinct from the P1, F and R1/NR1 prototypes. The pRA2 par region was effective in stabilizing both pRA2 and F mini‐replicons. Analysis of the nucleotide sequence revealed three potential coding regions that were designated parA, parB and parC. Through mutagenesis, parA and parB were found to be essential for partitioning function, whereas parC did not appear to be required. Using transcriptional reporter systems, it was demonstrated in vivo that ParB repressed par promoter activity by 60‐fold and that ParA had little effect on transcriptional activity. Primer extension analysis revealed that the par transcriptional start point was located 47 nucleotides upstream of the parA translational start codon. Based on this information, putative −10 and −35 transcriptional signals were identified, and their subsequent deletion resulted in a dramatic reduction in promoter activity. The par promoter region was also demonstrated to exert incompatibility towards a plasmid with an active pRA2 par system. Nested deletions in this region allowed the incompatibility determinant, designated parS, to be localized. Recombinant ParA and ParB proteins were overexpressed and purified by affinity chromatography. Through in vitro binding experiments, purified ParB was shown to interact specifically with the par promoter region. DNase I footprinting revealed that ParB not only binds to the conserved sequence 5′‐TCA AA(T/C) (G/C)CT CAA (A/T)A, which is present in three copies in the par promoter region, but also binds to the pRA2 partitioning site, parS. It appears that ParB has a dual role in pRA2 partitioning, being responsible for both the regulation of par transcription and the formation of a partition nucleoprotein complex at parS.
Formation of D‐alanyl‐lipoteichoic acid is required for adhesion and virulence of Listeria monocytogenes
Authors: Abachin Eric , Poyart Claire , Pellegrini Elisabeth , Milohanic Eliane , Fiedler Franz , Berche Patrick , Trieu‐Cuot Patrick 
Published: March 2003

SummaryThe dlt operon of Gram‐positive bacteria comprises four genes (dltA, dltB, dltC and dltD) that catalyse the incorporation of D‐alanine residues into the cell wall‐associated lipoteichoic acids (LTAs). In this work, we characterized the dlt operon of Listeria monocytogenes and constructed a D‐Ala‐deficient LTA mutant by inactivating the first gene (dltA) of this operon. The DltA− mutant did not show any morphological alterations and its growth rate was similar to that of the wild‐type strain. However, it exhibited an increased susceptibility to the cationic peptides colistin, nisin and polymyxin B. The virulence of the DltA− mutant was severely impaired in a mouse infection model (4 log increase in the LD50) and, in vitro, the adherence of the mutant to various cell lines (murine bone marrow‐derived macrophages and hepatocytes and a human epithelial cell line) was strongly restricted, although the amounts of surface proteins implicated in virulence (ActA, InlA and InlB) remains unaffected. We suggest that the decreased adherence of the DltA− mutant to non‐phagocytic and phagocytic cells might be as a result of the increased electronegativity of its charge surface and/or the presence at the bacterial surface of adhesins possessing altered binding activities. These results show that the D‐alanylation of the LTAs contributes to the virulence of the intracellular pathogen L. monocytogenes.
Post‐transcriptional enhancement of Escherichia coli bgl operon silencing by limitation of BglG‐mediated antitermination at low transcription rates
Authors: Dole Sudhanshu , Kühn Sandra , Schnetz Karin 
Published: March 2003

SummaryThe silent bgl operon of Escherichia coli is activated by spontaneous
mutations that derepress its promoter. In addition, expression depends on specific
transcriptional antitermination within the operon by the antiterminator protein BglG.
Here, we show that BglG‐mediated antitermination limits expression of the bgl
operon when the cellular transcription rate is low. The expression levels of chromosomally
encoded activated bgl operon alleles are low but increase significantly when
BglG protein is provided in trans or when the expression is rendered inde‐pendent
of BglG‐mediated antitermination by mutation of the terminator. Plasmid‐encoded activated
bgl operon alleles are expressed at high levels. Moreover, a moderate (threefold)
further increase in the transcription rate of chromosomally encoded activated bgl
operon alleles in an rpoS mutant can result in high (up to 50‐fold increased)
expression levels. These data show that the expression of the bgl operon does
not correlate linearly with its cellular transcription rate. Moderate differences
in the transcription initiation rate are amplified post‐transcriptionally into large
changes in the expression level of the operon by the requirement of a threshold for
BglG‐mediated antitermination. Implications for bgl operon regulation by global regulators H‐NS, RpoS and others are discussed.
Functional analysis of the enteropathogenicEscherichia colitype III secretion system chaperone CesT identifies domains that mediate substrate interactions
Authors: Delahay Robin M. , Shaw Robert K. , Elliott Simon J. , Kaper James B. , Knutton Stuart , Frankel Gad 
Published: March 2003

SummaryIn many Gram‐negative bacteria, a key indicator of pathogenic potential is the possession of a specialized type III secretion system, which is utilized to deliver virulence effector proteins directly into the host cell cytosol. Many of the proteins secreted from such systems require small cytosolic chaperones to maintain the secreted substrates in a secretion‐competent state. One such protein, CesT, serves a chaperone function for the enteropathogenicEscherichia coli(EPEC)translocatedintiminreceptor (Tir) protein, which confers upon EPEC the ability to alter host cell morphology following intimate bacterial attachment. Using a combination of complementary biochemical approaches, functional domains of CesT that mediate intermolecular interactions, involved in both chaperone–chaperone and chaperone–substrate associations, were determined. The CesT N‐terminal is implicated in chaperone dimerization, whereas the amphipathicα‐helical region of the C‐terminal, is intimately involved in substrate binding. By functional complementation of chaperone domains using theSalmonellaSicA chaperone to generate chaperone chimeras, we show that CesT–Tir interaction proceeds by a mechanism potentially common to other type III secretion system chaperones.