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1.
ABSTRACT Bean calico mosaic virus (BCMoV), a whitefly-transmitted geminivirus from Sonora, Mexico, was purified, and the genome components were cloned and sequenced. Purified viral fractions and cloned genome components were infectious by biolistic inoculation to bean, completing Koch's postulates for both. The B biotype of the whitefly Bemisia tabaci efficiently transmitted both native virus and progeny virus derived from cloned DNA inoculum. Host ranges of native virus and of progeny virus derived from cloned DNA were identical based upon whitefly and biolistic mediated transmission, respectively. BCMoV has a relatively wide experimental host range among begomoviruses known to infect bean, encompassing genera and species within the Fabaceae, Malvaceae, and Solanaceae. BCMoV has a bipartite genome, as do other New World begomoviruses. BCMoV DNA-A shared highest nucleotide sequence identities with squash leaf curl virus-E strain (SLCV-E) and cabbage leaf curl virus (CaLCV) at 80.1 and 80.7%, respectively. BCMoV DNA-B shared highest nucleotide sequence identity with SLCV-E at 70.7%. The common region (CR) sequences of BCMoV and SLCV-E are 73 to 76% identical; however, modular cis-acting elements within the CR involved in replication origin function and recognition are 100% conserved. Phy-logenetic analysis indicated that BCMoV DNA-A shares a most recent common ancestor with the DNA-A of two viruses that also occur in the Sonoran Desert, SLCV-E and Texas pepper virus (TPV-TAM), and CaLCV from Florida. In contrast, a phylogenetic analysis indicated that BCMoV DNA-B shares a most recent common ancestor with SLCV-E; whereas DNA-B of CaLCV clustered in a separate clade with pepper hausteco virus. Collectively, biological and molecular characteristics indicate that BCMoV is a distinct begomovirus species with the northernmost distribution of any begomovirus isolated from bean in the Americas. Furthermore, the phylogenetic relationships of begomovirus cognate components are not necessarily identical, suggesting that DNA-A and DNA-B of some begomoviruses may have different evolutionary histories. 相似文献
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ABSTRACT Cucurbit leaf curl virus (CuLCV), a whitefly-transmitted geminivirus previously partially characterized from the southwestern United States and northern Mexico, was identified as a distinct bipartite begomovirus species. This virus has near sequence identity with the previously partially characterized Cucurbit leaf crumple virus from California. Experimental and natural host range studies indicated that CuLCV has a relatively broad host range within the family Cucurbitaceae and also infects bean and tobacco. The genome of an Arizona isolate, designated CuLCV-AZ, was cloned and completely sequenced. Cloned CuLCV-AZ DNA A and B components were infectious by biolistic inoculation to pumpkin and progeny virus was transmissible by the whitefly vector, Bemisia tabaci, thereby completing Koch's postulates. CuLCV-AZ DNA A shared highest nucleotide sequence identity with Squash leaf curl virus-R (SLCV-R), SLCV-E, and Bean calico mosaic virus (BCaMV) at 84, 83, and 80%, respectively. The CuLCV DNA B component shared highest nucleotide sequence identity with BCaMV, SLCV-R, and SLCV-E at 71, 70, and 68%, respectively. The cis-acting begomovirus replication specificity element, GGTGTCCTGGTG, in the CuLCV-AZ origin of replication is identical to that of SLCV-R, SLCV-E, and BCaMV, suggesting that reassortants among components of CuLCV-AZ and these begomoviruses may be possible. Reassortment experiments in pumpkin demonstrated that both reassortants of CuLCV-AZ and SLCV-E A and B components were viable. However, for CuLCV-AZ and SLCV-R, only one reassortant (SLCV-R DNA A/CuLCV-AZ DNA B) was viable on pumpkin, even though the cognate component pairs of both viruses infect pumpkin. These results demonstrate that reassortment among sympatric begomovirus species infecting cucurbits are possible, and that, if generated in nature, could result in begomoviruses bearing distinct biological properties. 相似文献
3.
Stenger DC 《Phytopathology》1998,88(11):1174-1178
ABSTRACT Cloned genomes of the CFH, Worland, and Cal/Logan strains of beet curly top virus (BCTV) served as helper viruses to trans-replicate defective (D) DNAs that are incapable of self-replication due to deletions within the C1 open reading frame encoding the replication initiator (Rep) protein. The Logan Rep protein could trans-replicate a Logan-derived D DNA in a transient replication assay conducted in Nicotiana benthamiana leaf disks. However, the Logan Rep protein was unable to trans-replicate D DNAs derived from the CFH or Worland strains. In contrast, the Rep proteins of the CFH and Worland strains could trans-replicate CFH or Worland D DNAs, but not a Logan D DNA. These results indicate that the cis- and trans-acting replication specificity elements of the CFH and Worland strains are compatible and that the three strains of BCTV may be divided into two groupings based upon replication specificity determinants. A comparison of amino acid sequences of the Rep protein for the three BCTV strains suggests that the trans-acting replication specificity element may reside in one or more of 12 amino acid residues that are identical; in two amino acid residues that are chemically similar among the CFH and Worland Rep proteins, yet are different in the Logan Rep protein; or in both. Properties including replication specificity, nucleotide sequence identity, and symptom expression were used as criteria to propose separate species designations for each of the three BCTV strains. In this proposal, the Cal/ Logan strain retains the name BCTV, CFH and the closely related Iranian isolate are designated beet severe curly top virus, and Worland is designated beet mild curly top virus. 相似文献
4.
Kerns JG Cohen JD MacDonald AW Cho RY Stenger VA Carter CS 《Science (New York, N.Y.)》2004,303(5660):1023-1026
Conflict monitoring by the anterior cingulate cortex (ACC) has been posited to signal a need for greater cognitive control, producing neural and behavioral adjustments. However, the very occurrence of behavioral adjustments after conflict has been questioned, along with suggestions that there is no direct evidence of ACC conflict-related activity predicting subsequent neural or behavioral adjustments in control. Using the Stroop color-naming task and controlling for repetition effects, we demonstrate that ACC conflict-related activity predicts both greater prefrontal cortex activity and adjustments in behavior, supporting a role of ACC conflict monitoring in the engagement of cognitive control. 相似文献
5.
Liu PT Stenger S Li H Wenzel L Tan BH Krutzik SR Ochoa MT Schauber J Wu K Meinken C Kamen DL Wagner M Bals R Steinmeyer A Zügel U Gallo RL Eisenberg D Hewison M Hollis BW Adams JS Bloom BR Modlin RL 《Science (New York, N.Y.)》2006,311(5768):1770-1773
In innate immune responses, activation of Toll-like receptors (TLRs) triggers direct antimicrobial activity against intracellular bacteria, which in murine, but not human, monocytes and macrophages is mediated principally by nitric oxide. We report here that TLR activation of human macrophages up-regulated expression of the vitamin D receptor and the vitamin D-1-hydroxylase genes, leading to induction of the antimicrobial peptide cathelicidin and killing of intracellular Mycobacterium tuberculosis. We also observed that sera from African-American individuals, known to have increased susceptibility to tuberculosis, had low 25-hydroxyvitamin D and were inefficient in supporting cathelicidin messenger RNA induction. These data support a link between TLRs and vitamin D-mediated innate immunity and suggest that differences in ability of human populations to produce vitamin D may contribute to susceptibility to microbial infection. 相似文献
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Martin Kváč Michaela Kestřánová Martina Pinková Dana Květoňová Jana Kalinová Pavla Wagnerová Michaela Kotková Jiří Vítovec Oleg Ditrich John McEvoy Brianna Stenger Bohumil Sak 《Veterinary parasitology》2013,191(3-4):218-227
We describe the morphological, biological, and molecular characteristics of Cryptosporidium pig genotype II and propose the species name Cryptosporidium scrofarum n. sp. to reflect its prevalence in adult pigs worldwide. Oocysts of C. scrofarum are morphologically indistinguishable from C. parvum, measuring 4.81–5.96 μm (mean = 5.16) × 4.23–5.29 μm (mean = 4.83) with a length to width ratio of 1.07 ± 0.06 (n = 400). Oocysts of C. scrofarum obtained from a naturally infected pig were infectious for 8-week-old pigs but not 4-week-old pigs. The prepatent period in 8-week-old Cryptosporidium-naive pigs was 4–6 days and the patent period was longer than 30 days. The infection intensity of C. scrofarum in pigs was generally low, in the range 250–4000 oocysts per gram of feces. Infected pigs showed no clinical signs of cryptosporidiosis and no pathology was detected. Cryptosporidium scrofarum was not infectious for adult SCID mice, adult BALB/c mice, Mongolian gerbils (Meriones unguiculatus), southern multimammate mice (Mastomys coucha), yellow-necked mice (Apodemus flavicollis), or guinea pigs (Cavia porcellus). Phylogenetic analyses based on small subunit rRNA, actin, and heat shock protein 70 gene sequences revealed that C. scrofarum is genetically distinct from all known Cryptosporidium species. 相似文献
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Modelling effects of vector acquisition threshold on disease progression in a perennial crop following deployment of a partially resistant variety 
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下载免费PDF全文 Deployment of resistant varieties is a key strategy to mitigating economic losses due to arthropod‐transmitted plant pathogens of perennial crops. In many cases, the best available resistant traits for introgression confer only partial resistance. Plants displaying partial resistance have lower pathogen titres than susceptible counterparts, but remain hosts for the pathogen. As partially resistant varieties maintain yield after infection, infected plants are unlikely to be rogued (i.e. removed). Accordingly, there is a risk that partially resistant plants could serve as a source of inoculum for pathogen spread to susceptible plants. Here, a mathematical model that tracked spread of an arthropod‐transmitted pathogen in a plant population consisting of susceptible and partially resistant plants was used to identify a threshold acquisition rate from partially resistant plants that resulted in limited spread of the pathogen from partially resistant plants to susceptible plants. The acquisition threshold from partially resistant plants varied with parameters influenced by disease management decisions such as number of vectors per plant, vector turnover, replacement of susceptible plants, and proportion of plants that were partially resistant. In model simulations, effects of deploying a partially resistant variety on disease incidence in a susceptible variety depended on the extent to which pathogen spread among susceptible plants was suppressed and acquisition rates from partially resistant plants. Collectively, the results indicate that risk of partially resistant plants serving as inoculum sources could be assessed prior to deployment, thereby enabling design of complementary disease management tactics to minimize economic losses in susceptible varieties following deployment. 相似文献
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The emergence of the infectious disease chytridiomycosis is a major factor responsible for amphibian extinctions in pristine habitats. However, some populations coexist with Batrachochytrium dendrobatidis (Bd), the agent of chytridiomycosis, and others go extinct when Bd arrives. Variation of pathogen severity among populations may be explained by differences of antimicrobial skin peptides and anti-Bd skin bacteria. Previous work showed that a population of the frog Rana sierrae had a high proportion of individuals with at least one species of cultured anti-Bd skin bacteria and was coexisting with Bd for more than 6 years. A population of the closely related sister species Rana muscosa had a significantly lower proportion of individuals with anti-Bd bacteria, and the following year, it went extinct due to Bd. We extended previous work to include another sampling of the R. sierrae population coexisting with Bd and found that, although the anti-Bd bacterial community somewhat differed, both populations had a high proportion of individuals with antifungal bacteria. We also included a population of R. muscosa that was naïve of Bd and predicted to go extinct once Bd emerged since that was the fate of neighboring populations. However, the naïve R. muscosa population had a high proportion of antifungal bacteria, which suggested that the population might survive if Bd emerged. Two years later, the population was surviving with Bd endemic. Variation in the proportion of individuals with anti-Bd skin bacteria appears to explain why some populations persist when Bd emerges in a population. 相似文献
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The ability to detect, quantify, and differentiate nonculturable mycoplasma-like organisms (MLOs) would greatly facilitate epidemiological and taxonomical studies of this unique group of plant and insect pathogens. DNA isolated from extracts of insects infected with the Western X-disease MLO was cloned in Escherichia coli. X-disease-specific clones, when labeled and used as probes, readily detected X-disease MLOs in infected plants and insects but did not hybridize with DNA from healthy plants or insects, or from several other plant pathogenic MLOs or spiroplasmas. These methods provide both a sensitive diagnostic tool and a basis for genetically differentiating MLOs. 相似文献
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