Biomedical subjects

S Ellwood

Publications and source records attributed to S Ellwood.

7 recordsLinked to original sources

PubMed2001

Broad-spectrum mildew resistance in Arabidopsis thaliana mediated by RPW8.

Plant disease resistance (R) genes control the recognition of specific pathogens and activate subsequent defense responses. We show that the Arabidopsis thaliana locus RESISTANCE TO POWDERY MILDEW8 (RPW8) contains two naturally polymorphic, dominant R genes, RPW8.1 and RPW8.2, which individually control resistance to a broad range of powdery mildew pathogens. Although the predicted RPW8.1 and RPW8.2 proteins are different from the previously characterized R proteins, they induce localized, salicylic acid-dependent defenses similar to those induced by R genes that control specific resistance. Apparently, broad-spectrum resistance mediated by RPW8 uses the same mechanisms as specific resistance.

Alleles↗

PubMed1999

Comparison of Erysiphe cichoracearum and E. cruciferarum and a survey of 360 Arabidopsis thaliana accessions for resistance to these two powdery mildew pathogens.

In previous work, UEA1 and UCSC1, two geographically distinct, powdery mildew isolates, were recognized for their ability to infect Arabidopsis thaliana. We have clarified the identity of these isolates by determining their host ranges, reexamining their morphology, and comparing their DNA sequences for the 5.8S ribosomal RNA and two flanking internal transcribed spacer sequences. These experiments confirm that UEA1 is a member of Erysiphe cruciferarum and that UCSC1 belongs to E. cichoracearum. Interactions of the two Erysiphe isolates with 360 A. thaliana accessions were examined to provide a comprehensive profile of naturally occurring powdery mildew resistance in this weedy species. The majority of A. thaliana accessions (213) were susceptible to both isolates. Among the accessions exhibiting some degree of resistance, most (84) responded differentially to UEA1 and UCSC1 and the remainder were resistant to both isolates. Notably, resistance to UCSC1 cosegregated with RPW7, a locus previously demonstrated to confer resistance to UEA1 in Ms-0 x Landsberg (erecta) crosses. With this large collection of resistant accessions, questions about species specificity, genetic diversity and the evolution of resistance to powdery mildews can be addressed.

Arabidopsis↗

PubMed1997

Characterization of three loci controlling resistance of Arabidopsis thaliana accession Ms-0 to two powdery mildew diseases.

Arabidopsis thaliana accession La-er was susceptible, and accession Ms-0 was resistant, to powdery mildew diseases caused by Erysiphe cruciferarum UEA1 and E. cichoracearum UCSC1. The resistance reaction phenotype of A. thaliana Ms-0 to both pathogens was characterized, and the resistance loci were genetically mapped. Growth of E. cruciferarum UEA1 on Ms-0 leaves was arrested after formation of the first appressorium: the underlying host epidermal cell collapsed, and occasionally there was necrosis of one or two host mesophyll cells. Growth of E. cichoracearum UCSC1 on Ms-0 leaves was arrested after emergence of several germ tubes from the conidium, and there was necrosis of host mesophyll cells at the sites of infection. Examination of F2 progeny of a cross La-er x Ms-0 indicated that two independently-segregating dominant loci were required for resistance to E. cruciferarum UEA1. One locus, named RPW6, was genetically mapped to chromosome 5, in a 5.6 cM interval flanked by pCITf16 and PI. The other locus, named RPW7, mapped to chromosome 3 in a 8.5 cM interval flanked by CDC2A and AFC1. Independent effects of RPW6 and RPW7 on E. cruciferarum UEA1 could be detected by quantitative measurements of growth of mycelium and production of conidia. Resistance to E. cichoracearum UCSC1 mapped to a single locus, named RPW8, at a location on chromosome 3 which we could not distinguish from RPW7. Evidently, RPW7 and RPW8 define either a complex resistance locus, or a common resistance gene with dual specificity.

Arabidopsis↗

PubMed1990

Defective viral DNA ameliorates symptoms of geminivirus infection in transgenic plants.

Nicotiana benthamiana was transformed with a single copy of a tandem repeat of subgenomic DNA B isolated from plants infected with a Kenyan isolate of the bipartite geminivirus African cassava mosaic virus. Symptoms in transformed plants were less severe than in nontransformed controls when challenged with virus or cloned DNA of Kenyan or Nigerian isolates. Symptom amelioration was associated with the mobilization and amplification of the subgenomic DNA, producing a comparable reduction in the amount of DNA specific to each genomic component. The disproportionate reduction in the levels of full-length components (DNA A, 20%; DNA B, 70%) indicates that the episomally replicating subgenomic DNA has been amplified at the expense of full-length DNA B to three times the level of the latter. Serial infection of transformants resulted in a further decrease in symptom severity and viral DNA levels. No differences were observed in the severity of symptoms or levels of viral DNA when transformants and controls were challenged with the related geminiviruses beet curly top virus and tomato golden mosaic virus, demonstrating the specific nature of the interaction. Analysis of infected tissue showed that tomato golden mosaic virus was unable to amplify the subgenomic DNA. However, since the production of subgenomic DNA is possibly a common feature of the bipartite geminiviruses, this approach might contribute to the production of plants showing increased tolerance to a number of economically important viral diseases.

Blotting, Southern↗

PubMed1988

Delimitation of essential genes of cassava latent virus DNA 2.

Insertion and deletion mutagenesis of both extended open reading frames (ORFs) of cassava latent virus DNA 2 destroys infectivity. Infectivity is restored by coinoculating constructs that contain single mutations within different ORFs. Although frequent intermolecular recombination produces dominant parental-type virus, mutants can be retained within the virus population indicating that they are competent for replication and suggesting that rescue can occur by complementation of trans acting gene products. By cloning specific fragments into DNA 1 coat protein deletion vectors we have delimited the DNA 2 coding regions and provide substantive evidence that both are essential for virus infection. Although a DNA 2 component is unique to whitefly-transmitted geminiviruses, the results demonstrate that neither coding region is involved solely in insect transmission. The requirement for a bipartite genome for whitefly-transmitted geminiviruses is discussed.

Amino Acid Sequence↗

PubMedDate not supplied

The poster presentation as an educational tool.

The authors describe their experiences in using the poster presentation to develop undergraduate nursing students in the scholarly role of professional nursing practice. The posters were used as a means for students to communicate their accomplishments in implementation and evaluation of an innovative clinical project. Methods for development, exhibition, and evaluation of the poster project are described.

Audiovisual Aids↗

PubMedDate not supplied

Pricing in the NHS.

Since the introduction of the NHS internal market, it has been necessary to price health care for contracts and extra contractual referrals. Internal markets, like conventional markets, operate via a pricing mechanism. This article describes the NHS pricing principles and the development of NHS pricing for acute hospital services in the first 5 years of the market.

Contract Services↗