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951.
Casjens SR Mongodin EF Qiu WG Dunn JJ Luft BJ Fraser-Liggett CM Schutzer SE 《Journal of bacteriology》2011,193(24):6995-6996
Human Lyme disease is commonly caused by several species of spirochetes in the Borrelia genus. In Eurasia these species are largely Borrelia afzelii, B. garinii, B. burgdorferi, and B. bavariensis sp. nov. Whole-genome sequencing is an excellent tool for investigating and understanding the influence of bacterial diversity on the pathogenesis and etiology of Lyme disease. We report here the whole-genome sequences of four isolates from two of the Borrelia species that cause human Lyme disease, B. afzelii isolates ACA-1 and PKo and B. garinii isolates PBr and Far04. 相似文献
952.
Persson T Benson DR Normand P Vanden Heuvel B Pujic P Chertkov O Teshima H Bruce DC Detter C Tapia R Han S Han J Woyke T Pitluck S Pennacchio L Nolan M Ivanova N Pati A Land ML Pawlowski K Berry AM 《Journal of bacteriology》2011,193(24):7017-7018
Members of the noncultured clade of Frankia enter into root nodule symbioses with actinorhizal species from the orders Cucurbitales and Rosales. We report the genome sequence of a member of this clade originally from Pakistan but obtained from root nodules of the American plant Datisca glomerata without isolation in culture. 相似文献
953.
Duncan AB Fellous S Kaltz O 《Evolution; international journal of organic evolution》2011,65(12):3462-3474
Evolutionary costs of parasite resistance arise if genes conferring resistance reduce fitness in the absence of parasites. Thus, parasite-mediated selection may lead to increased resistance and a correlated decrease in fitness, whereas relaxed parasite-mediated selection may lead to reverse evolution of increased fitness and a correlated decrease in resistance. We tested this idea in experimental populations of the protozoan Paramecium caudatum and the parasitic bacterium Holospora undulata. After eight years, resistance to infection and asexual reproduction were compared among paramecia from (1) "infected" populations, (2) uninfected "naive" populations, and (3) previously infected, parasite-free "recovered" populations. Paramecia from "infected" populations were more resistant (+12%), but had lower reproduction (-15%) than "naive" paramecia, indicating an evolutionary trade-off between resistance and fitness. Recovered populations showed similar reproduction to naive populations; however, resistance of recently (<3 years) recovered populations was similar to paramecia from infected populations, whereas longer (>3 years) recovered populations were as susceptible as naive populations. This suggests a weak, convex trade-off between resistance and fitness, allowing recovery of fitness, without complete loss of resistance, favoring the maintenance of a generalist strategy of intermediate fitness and resistance. Our results indicate that (co)evolution with parasites can leave a genetic signature in disease-free populations. 相似文献
954.
Starch-branching enzyme IIa is required for proper diurnal cycling of starch in leaves of maize 总被引:2,自引:0,他引:2
Starch-branching enzyme (SBE), a glucosyl transferase, is required for the highly regular pattern of α-1,6 bonds in the amylopectin component of starch. In the absence of SBEIIa, as shown previously in the sbe2a mutant of maize (Zea mays), leaf starch has drastically reduced branching and the leaves exhibit a severe senescence-like phenotype. Detailed characterization of the maize sbe2a mutant revealed that SBEIIa is the primary active branching enzyme in the leaf and that in its absence plant growth is affected. Both seedling and mature sbe2a mutant leaves do not properly degrade starch during the night, resulting in hyperaccumulation. In mature sbe2a leaves, starch hyperaccumulation is greatest in visibly senescing regions but also observed in green tissue and is correlated to a drastic reduction in photosynthesis within the leaf. Starch granules from sbe2a leaves observed via scanning electron microscopy and transmission electron microscopy analyses are larger, irregular, and amorphous as compared with the highly regular, discoid starch granules observed in wild-type leaves. This appears to trigger premature senescence, as shown by an increased expression of genes encoding proteins known to be involved in senescence and programmed cell death processes. Together, these results indicate that SBEIIa is required for the proper diurnal cycling of transitory starch within the leaf and suggest that SBEIIa is necessary in producing an amylopectin structure amenable to degradation by starch metabolism enzymes. 相似文献
955.
The role of alpha-glucosidase in germinating barley grains 总被引:1,自引:0,他引:1
Stanley D Rejzek M Naested H Smedley M Otero S Fahy B Thorpe F Nash RJ Harwood W Svensson B Denyer K Field RA Smith AM 《Plant physiology》2011,155(2):932-943
The importance of α-glucosidase in the endosperm starch metabolism of barley (Hordeum vulgare) seedlings is poorly understood. The enzyme converts maltose to glucose (Glc), but in vitro studies indicate that it can also attack starch granules. To discover its role in vivo, we took complementary chemical-genetic and reverse-genetic approaches. We identified iminosugar inhibitors of a recombinant form of an α-glucosidase previously discovered in barley endosperm (ALPHA-GLUCOSIDASE97 [HvAGL97]), and applied four of them to germinating grains. All four decreased the Glc-to-maltose ratio in the endosperm 10 d after imbibition, implying inhibition of maltase activity. Three of the four inhibitors also reduced starch degradation and seedling growth, but the fourth did not affect these parameters. Inhibition of starch degradation was apparently not due to inhibition of amylases. Inhibition of seedling growth was primarily a direct effect of the inhibitors on roots and coleoptiles rather than an indirect effect of the inhibition of endosperm metabolism. It may reflect inhibition of glycoprotein-processing glucosidases in these organs. In transgenic seedlings carrying an RNA interference silencing cassette for HvAgl97, α-glucosidase activity was reduced by up to 50%. There was a large decrease in the Glc-to-maltose ratio in these lines but no effect on starch degradation or seedling growth. Our results suggest that the α-glucosidase HvAGL97 is the major endosperm enzyme catalyzing the conversion of maltose to Glc but is not required for starch degradation. However, the effects of three glucosidase inhibitors on starch degradation in the endosperm indicate the existence of unidentified glucosidase(s) required for this process. 相似文献
956.
957.
Many antagonistic species attack plants and consume specific plant parts. Understanding how these antagonists affect plant
fitness individually and in combination is an important research focus in ecology and evolution. We examined the individual
and combined effects of herbivory, nectar robbing, and pre-dispersal seed predation on male and female estimates of fitness
in the host plant Ipomopsis aggregata. By examining the effects of antagonists on plant traits, we were able to tease apart the direct consumptive effects of antagonists
versus the indirect effects mediated through changes in traits important to pollination. In a three-way factorial field experiment,
we manipulated herbivory, nectar robbing, and seed predation. Herbivory and seed predation reduced some male and female fitness
estimates, whereas plants tolerated the effects of robbing. The effects of herbivory, robbing, and seed predation were primarily
additive, and we found little evidence for non-additive effects of multiple antagonists on plant reproduction. Herbivory affected
plant reproduction through both direct consumptive effects and indirectly through changes in traits important to pollination
(i.e., nectar and phenological traits). Conversely, seed predators primarily had direct consumptive effects on plants. Our
results suggest that the effects of multiple antagonists on estimates of plant fitness can be additive, and investigating
which traits respond to damage can provide insight into how antagonists shape plant performance. 相似文献
958.
Analysis of an organism’s genetic diversity requires a method that gives reliable, reproducible results. Microsatellites are
robust markers, however, detection of allele sizes can be difficult with some systems as well as consistency among laboratories.
In this study, our two laboratories used 219 isolates of Phytophthora sojae to compare three microsatellite methods. Two capillary electrophoresis methods, the Applied Biosystems 3730 Genetic Analyzer
and the CEQ 8000 Genetic Analysis system, detected an average of 2.4-fold more alleles compared to gel electrophoresis with
a mean of 8.8 and 3.6 alleles per locus using capillary and gel methods, respectively. The two capillary methods were comparable,
although allele sizes differed consistently by an average of 3.2 bp across isolates. Differences between capillary methods
could be overcome if reference standard DNA genotypes are shared between collaborating laboratories. 相似文献
959.
Sproston EL Ogden ID MacRae M Dallas JF Sheppard SK Cody AJ Colles FM Wilson MJ Forbes KJ Strachan NJ 《Applied and environmental microbiology》2011,77(18):6579-6586
Campylobacter jejuni and C. coli were quantified and typed, using multilocus sequence typing (MLST), from fecal samples collected from a mixed cattle and sheep farm during summer. Cattle had a significantly higher prevalence than sheep (21.9% [74/338] and 14.0% [30/214], respectively), but both decreased over time. There were no differences in the average Campylobacter concentrations shed by cattle (600 CFU g(-1)) and sheep (820 CFU g(-1)), although sheep did show a significant temporal reduction in the number of Campylobacter organisms shed in their feces. A total of 21 different sequence types (STs) (97.7% C. jejuni, 2.3% C. coli) were isolated from cattle, and 9 different STs were isolated from sheep (40.6% C. jejuni, 59.4% C. coli). The Campylobacter population in cattle was relatively stable, and the frequencies of genotypes isolated showed little temporal variation. However, the composition of subtypes isolated from sheep did show significant temporal differences. The cattle and sheep consistently showed significant differences in their carriage of Campylobacter species, STs, and CCs despite the fact that both were exposed to the same farming environment. This work has highlighted the patterns of a Campylobacter population on a ruminant farm by identifying the existence of both temporal and between-host variations. 相似文献
960.
A major challenge facing studies of major histocompatibility complex (MHC) evolution in birds is the difficulty in genotyping
alleles at individual loci, and the consequent inability to investigate sequence variation and selection pressures for each
gene. In this study, four MHC class I loci were isolated from the red-billed gull (Larus scopulinus), representing both the first characterized MHCI genes within Charadriiformes (shorebirds, gulls, and allies) and the first
full-length MHCI sequences described outside Galloanserae (gamebirds + waterfowl). Complete multilocus genotypes were obtained
for 470 individuals using a combination of reference-strand conformation analysis and direct sequencing of gene-specific amplification
products, and variation of peptide-binding region (PBR) exons was surveyed for all loci. Each gene is transcribed and has
conserved sequence features characteristic of antigen-presenting MHCI molecules. However, higher allelic variation, a more
even allele frequency distribution, and evidence of positive selection acting on a larger number of PBR residues suggest that
only one locus (Lasc-UAA) functions as a major classical MHCI gene. Lasc-UBA, with more limited variation and PBR motifs that
encompass a subset of Lasc-UAA diversity, was assigned a putative minor classical function, whereas the divergent and largely
invariant binding-groove motifs of Lasc-UCA and -UDA are suggestive of nonclassical loci with specialized ligand-binding roles. 相似文献