1,720,985 research outputs found
Salmonella Rissen Φ1: a molecular switch
No full textIntroduction: Bacteria develop resistance against phages by losing the phage receptor or reducing its binding specificity or by a temporary change of phage receptor specificity. Here we describe the phage resistance mechanism adopted by S. Rissen which acts through a molecular switch.
Material & Methods: Phage was isolated from the S. Rissen strain (RW) and used to select the phage resistant strain RRφ1+. We evaluate both the differences in bacterial morphology and the genetic variations between the two strains by biochemical and comparative genomic analyses.
Results: Biochemical analyses showed that the presence of the phage influences biofilm production, phage resistance and the switch of the O-antigen from smooth to rough, Genomic analysis showed that the sensitive and resistant strains differ by 10 genes. Only the phosphomannomutase_1 and 2 genes, involved in mannose synthesis pathway, showed different expression levels. The SNP of the two genes are located near HTs known to regulate phase variation. We used S rissen to see whether a character under strong selection pressure- such as phage resistance is repeatable. In four independent experiment phage resistance was acquired by the same molecular mechanism.
Conclusion: S. rissen uses the same and evolutionary flexible tool (phase variation) to control several characters: biofilm production, phage resistance, and O-antigen structure
FUNCTIONAL AND MOLECULAR ANALYSIS OF an1 MYB TRANSCRIPTIONAL FACTOR INVOLVED IN ANTHOCYANIN PRODUCTION IN POTATO
No full textThe wild side of potato: insights into the genome sequence of the stress-tolerant S. commersonii Dun
No full textSolanum commersonii is a potato species native to Central and South America. Despite being genetically isolated from cultivated potato, in the past few years it has garnered significant research interest because it exhibits high tolerance to both biotic and abiotic stresses. Among the abiotic stresses, particularly interesting are its freezing tolerance and capacity to cold acclimatize. Little is understood of the genetic determi- nants and mechanisms beyond its resistance traits. This is partially due to the lack of genomic resources for potato germplasm. The group at the University of Naples has recently decoded, for the first time, the genome of S. commersonii, ushering in a new era of whole-genome sequencing of wild potato relatives. After illustrating the genome structure and organization of this species and its intrigffuing evolutionary roots, this chapter describes findings relative to the identification of the candidate genes for cold stress tolerance. The genome sequence of S. commersonii will pave the way to an understanding of the molecular dynamics that have given this species so many adaptive characteristics
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
THE GENOME SEQUENCE OF SOLANUM COMMERSONII DUN., A VALUABLE SOURCE OF RESISTANT GENES FOR POTATO BREEDING
No full textThe tetraploid cultivated potato (Solanum tuberosum, 2n=4x=48) is the fourth most important crop for humans. Since the cultivated varieties are derived from a small number of genotypes, potato is characterized by a low genetic variability. Fortunately, it has about 200 wild tuber-bearing relatives that represent an incredible source of genetic variation and a reservoir of useful genes for the development of new varieties with improved resistance, nutrient content and productivity. However, several constrains hamper wild germplasm utilization. Among them, sexual incompatibility between wild and cultivated species and linkage drag make classical breeding methods time-consuming and laborious. In addition, few genomic resources ara available that can help breeders in their work of producing genetic variability and select superior clones. For all these reasons there has been an under-utilization of the potato genetic resources. The objective of this research was to develop new genomic tools that enable the expansion of the existing breeding strategies for an efficient exploitation of potato genetic resources.
Nowadays, sequencing technology combined with the availability of the S. tuberosum reference genome allows the characterization of the genetic variations affecting the cultivated potato. However, no genome sequence is available for a wild potato species. Therefore our study was addressed to sequence the genome of one of the most important tuber-bearing species, S. commersonii (2n=2x=24), that possesses several resistances to biotic and abiotic stresses. We de novo sequenced the genome of S. commersonii to 103x coverage using Illumina technology producing a 862 Mb genome. On the basis of sequence homology, 39,290 protein-coding genes were predicted and supported by transcript data and further annotation. We used the orthology and paralogy proteins relationships for the reconstruction of the complete collection of evolutionary histories of all S. commersonii protein-coding genes across a phylogeny of 12 sequenced plants. Interestingly, we discovered 8,578 S. commersonii-specific gene families lacking in S. tuberosum. HMM models and manual curation were used to annotate 2,523 non-redundant NBS-encoding R gene candidates, and comparison analysis with potato R-genes supported the idea that a locus rearrangement occurred during evolution. In order to find out the genetic determinants of S. commersonii resistance to low temperatures and capacity to cold harden, we focused on genes involved in abiotic stress response. Out of roughly 2,800 cold resistance genes, we found that 126 were unique in S. commersonii. To investigate further, a transcriptome analysis by using a custom microarray chip was carried out in two different experimental conditions. This allowed us to detect all the expressed genes involved in cold acclimation and to hypothesize the molecular dinamics at the basis of the different response to low temperature in S. commersonii vs. S. tuberosum. The experimental work carried out in this PhD reports the first genome sequence for a wild relative of the cultivated potato The genome sequence of S. commersonii has substantially increased our understanding on wild potatoes and these information might be used to overcome the limitations due to the low variability of domesticated germplasm. It will also offer the potential of better using wild relatives for potato breeding and evolutionary studies
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
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