1,720,987 research outputs found
Characterisation of Potential Fungal Disease Resistance Genes in Banana
No full textBananas are an extremely important crop, serving as both a staple food in developing countries and as a dessert fruit in Western society. Two of the most devastating pathogens currently affecting both commercial and subsistence banana production are Fusarium oxysporum (Foc; causal agent of Fusarium wilt) and Mycosphaerella species (causal agent of black and yellow Sigatoka). Conventional breeding programs designed to improve the disease resistance characteristics of the commercially elite Cavendish cultivar have, thus far, been largely unsuccessful. Genetic engineering is now regarded as the most promising method to generate enhanced disease resistance in banana. In other crops and model species, strategies to enhance disease resistance have included the transgenic expression of defense-related genes such as; disease resistance genes (R genes), downstream signaling genes (eg. NPR1, non-pathogenesis related) and antimicrobial peptides (AMPs). The overall aims of this research were to amplify and compare the nucleotide binding site (NBS) domains of potential disease resistance genes from disease resistant and disease susceptible banana cultivars. To isolate and compare complete R gene sequences from these cultivars. To generate transgenic Lady Finger banana plants expressing the D4E1 antimicrobial peptide under the control of two different promoters and finally to assess extracts from these plants for their ability to inhibit the growth of Foc Race1.
Using degenerate primers, the NBS domains of six resistance gene candidate (RGC) sequences were amplified from the disease resistant cultivar Calcutta 4 (C4) and the disease susceptible cultivar Cavendish (Cav). The RGC 1, 2, 5 and 6 sequences showed similarity to previously characterized R gene sequences isolated from monocotyledonous plant species, while RGCs 3 and 4 showed similarity to R genes which form part of the Fusarium wilt resistance locus isolated from the dicotyledonous species, Lycopersicon esculentum; as well as other monocotyledonous R genes. RGCs 1-4 and 6 were present and transcriptionally active in both C4 and Cav, whereas RGC-5 was present in Cav only and was not transcribed. The transcripts could not be detected by Northern analysis, which is consistent with previous reports that R genes are constitutively transcriptionally active at only low levels. The NBS domains of RGCs 1-6 showed less than 65% similarity (amino acid level) to one another but when each individual RGC isolated from the C4 and Cav gDNA and cDNA templates was compared the sequences showed greater than 97% similarity (amino acid level). Comparative sequence analysis revealed amino acid positions that were consistently different between the C4 and Cav clones. Southern analysis revealed that RGC 1-5 were present in both the C4 and Cav genomes in only low copy number (1-2 gene copies with 1-3 alleles), whereas RGC-6 showed high copy number in both cultivars.
Complete RGC sequences were subsequently amplified by RNA-ligase-mediated (RLM) -RACE and 3'-RACE using specific primers designed to each of the RGC 1-4 NBS domains. Amplicons for each RGC were assembled to form potentially complete RGC sequences. Analysis of the sequences revealed the presence of coiled coil (CC) motifs in two of the amino terminal sequences while leucine rich repeats (LRRs) were identified at the carboxy terminal of all sequences. Multiple 3'-RACE products were amplified for each RGC sequence. Although the polyadenylated products were of different lengths, the sequences were greater than 98% identical at the amino acid level (except an RGC 3 clone which was 91-95% identical to the other RGC 3 clones due to a 37 amino acid deletion). Specific primers used to amplify each complete RGC sequence from both C4 and Cav DNA revealed that: RGC 1 (3.53 kbp) could be amplified from both C4 and Cav; RGCs 2 (2.99 kbp) and 4 (4.44 kbp) could be amplified from only Cav, however, the proposed truncations of these sequences (RGC 2: 1.3 kbp, RGC 4: 2.8 kbp and 2.9 kbp) could be amplified from both cultivars; RGC 3 (4.57 kbp) could not be amplified from either C4 or Cav, however, the three shorter sequences (1.96 kbp, 1.34 kbp and 1.28 kbp) could be amplified from both templates. The functional significance of the truncated sequences is currently unknown, however, truncated sequences have been detected in a number of R gene families isolated from other crops. No major sequence differences, such as deletions/insertions or early stop codons, were identified between the RGC sequences amplified from C4 as compared to Cav (greater than 91% amino acid similarity) and no sequence was identified as being present in the susceptible but absent from the resistant cultivar. However, comparative analysis of multiple clones isolated from C4 and Cav did reveal amino acid residues that were consistently different between the two cultivars. These differences may result in differing resistance capabilities, functional genomics studies would need to be undertaken to determine this.
It has been proposed that CC-NBS-LRR type R genes employ NDR1/HIN1-like (NHL) proteins, after pathogen invasion is detected, in the signaling process that ultimately leads to the elaboration of a defense response. A NHL partial sequence (420 bp) was amplified from the C4 banana cultivar. The complete sequence of this gene (termed NHL-1) was isolated using RLM and 3'-RACE technologies (576 bp and 535 bp amplicons, respectively) and subsequently the 1.106 kbp sequence was PCR amplified from both the C4 and Cav cultivars. The banana NHL-1 gene contained conserved motifs/domains previously identified within other NHL-type gene sequences. These included a signal peptide motif, a transmembrane domain and three previously identified conserved motifs. Based on current research into NHL type genes, the banana NHL-1 sequence may not be useful as a transgene to enhance disease resistance in elite cultivars. However, it potentially plays an important role in the defense response signal transduction pathway and therefore will further our understanding of plant-pathogen interactions in banana.
Transgenic Lady Finger banana plants expressing the D4E1 antimicrobial peptide under the control of either the maize polyubiquitin (Ubi) or banana bunchy top virus (BBTV) DNA-6 (Bt6.1) promoters were generated. These plants were subsequently assessed for the ability of their crude protein extracts to inhibit the germination of Fusarium oxysporum f.sp. cubense Race1 conidia in vitro. These anti-fungal bioassays revealed that fungal colony growth was reduced by 37-100% using extracts from the pUbi-D4E1 transgenic lines and 89-99% using extracts from the pBt6.1-D4E1 transgenic lines. The transgenic lines are currently undergoing multiplication in preparation for glasshouse and small plant challenge trials for resistance to Fusarium wilt. These preliminary results suggest that D4E1 may be useful in enhancing disease resistance in banana
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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