1,721,058 research outputs found
International Bank for the Glomeromycota
No full textArbuscular mycorrhiza is a mutualistic symbiosis between the majority of land plants and fungi from the phylum Glomeromycota. The fungi are obligate symbionts and cannot be cultivated without their host plant. About 300 species of Glomeromycota have been described. The plant provides carbohydrates from photosynthesis whereas the fungal partner improves mineral nutrient transport. Other, more complex beneficial effects of the association involve increased pathogen resistance and improvement of soil structure. Arbuscular mycorrhiza is therefore an essential factor for plant ecosystems and has considerable potential to be used for improving crop production.
The International Bank for the Glomeromycota (IBG) was initiated in a European research network, originally it was called "Banque Européenne de Glomales (BEG)", a name which was modified later to reflect its outreach beyond Europe and changes in the nomenclature of arbuscular mycorrhizal fungi.
Its missions are: Provide, upon request or within the framework of research projects, high-quality germplasm of well-characterized arbuscular mycorrhizal fungi. Maintain reference cultures for industrial partners. Organize training courses and classes about identification and cultivation of Glomeromycota. Provide a database of informations about IBG isolates.
The core collection at INRAE Dijon currently harbors about 320 cultures of 40 isolates in 32 species. The fungi are grown continually in association with their host plants. Upon request via the collection website (www.i-beg.eu), small quantities of inoculum a maximum of three isolates are provided. Special arrangements are made for cooperation projects
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Molecular community and population studies of arbuscular mycorrhizal fungi (Glomeromycota)
No full textLa symbiose mycorhizienne à arbuscules, dont l’apparition est conjointe à celle des plantes terrestres il y a 460 millions d’années, est une association mutualiste à bénéfices réciproques qui s’instaure entre la plupart des plantes terrestres, y compris celles cultivées, et des microorganismes ubiquitaires du sol que sont les champignons mycorhiziens à arbuscules (CMA, phylum des Glomeromycota). Lors cette symbiose, le fort potentiel d’amélioration de la nutrition minérale des plantes, et donc de la production végétale, est un atout dans le contexte mondial actuel d’augmentation de la demande de la production agricole. Afin d’optimiser les services écosystémiques des CMA dans les écosystèmes et en particulier les agroécosystèmes, la maîtrise de cette symbiose en ingénierie écologique nécessite la compréhension des mécanismes complexes qui régissent la dynamique de cette symbiose dans ces écosystèmes. Pour cela, nous avons étudié la diversité des communautés et des populations de CMA dans les agroécosystèmes à différentes échelles spatiales et sous l’influence de différentes pratiques culturales par des techniques d’empreintes moléculaires: séquençage haut-débit et polymorphisme de longueur de fragments de restriction. Les résultats obtenus montrent que la structuration de la diversité des CMA est influencée par le type d’usage de sol (prairie vs. culture), les pratiques culturales (retournement du sol, fertilisation et système de culture) ainsi que par les facteurs abiotiques (e.g. pH du sol). En conclusion, ces différents facteurs sont à prendre en compte dans l’optimisation des services écosystémiques des CMA.The arbuscular mycorrhizal symbiosis, which appeared at the same time as land plants, 460 million years ago, is a mutualistic beneficial association between most land plants, including those cultivated, and arbuscular mycorrhizal fungi (AMF). AMF, from the Glomeromycota phylum, are widespread soil microorganisms needing a photosynthetic host to complete their life cycle (obligate symbionts). The great potential of plant mineral nutrition improvement and crop production increased during this symbiosis, make AMF an asset in the context of an increase in the demand of world food crop production. The control of that symbiosis by ecology engineering in order to improve ecosystem services, especially in agroecosystems, needs to better understand the mechanisms regulating its dynamic. Therefore, we studied community and population diversity of AMF under influences of different agricultural practices at several spatial scales using genetic fingerprinting methods: high-throughput sequencing and restriction fragment length polymorphism. Results show that AMF diversity is structured by land use type (grassland vs. arable fields), cultural practices (soil disturbance, fertilizations, culturing systems) as well as environmental factors (e.g. soil pH). In conclusion, those different factors have to taken in account in AMF ecosystemic service managing
Gene induction during plant-microbe interactions : the role of chitinases during fungal infection and the investigation of mycorrhiza-induced genes in the model plant "M. truncatula"
Full text linkIn this thesis, the model legume Medicago truncatula was used for research on plant-microbe
interactions. Unlike most other plants, legumes are able to form two distinct root symbioses.
Together with soil-borne fungi of the Glomeromycota, they form the arbuscular mycorrhiza
and with rhizobial bacteria, they form nitrogen fixing root nodules. Here, plant responses to
these symbiotic microbes were investigated, and compared to the plant's defence response
against antagonistic microbes.
Plant chitinases have an important role in the interplay between plants and microbes; they
have been shown to act as defence-related antifungal enzymes, but they seem to be
involved in symbiotic processes as well. In previous work, genes encoding eight different
chitinases were identified in M. truncatula. The main part of this thesis is dedicated to an indepth
study of these genes with regard to their regulation and function. Additionally, the
expression patterns of genes that are related to the arbuscular mycorrhizal interaction of M.
truncatula were analysed in order to further explore this important symbiosis.
In roots of the M. truncatula ecotype R108-1, expression of the gene Mtchit5, encoding a
class V chitinase, was induced during nodule formation after infection with wild type rhizobia,
but not in response to pathogenic fungi or arbuscular mycorrhizal fungi. Mtchit5 transcripts
were first detectable in roots forming nodule primordial and accumulated during nodule
ripening. The gene was induced in response to purified Nod factors and also in ineffective
white nodules formed by a mutant rhizobial strain. Phylogenetic analysis of the deduced
amino acid sequence revealed that the putative Mtchit5 chitinase forms a separate clade
within class V chitinases of plants. These results, together with the additional finding that
Mtchit5 expression is high in flowers, indicate that Mtchit5 is a putative early nodulin that is
specifically induced by rhizobia in roots and may have a function in plant developmental
processes.
The gene Mtchit4, encoding a class IV chitinase, is induced during infection by pathogenic
fungi in roots of M. truncatula but not during mycorrhiza formation. During nodule formation,
Mtchit4 was strongly induced only in the M. truncatula ecotype Jemalong A17 after infection
with wild-type rhizobium strains. Its expression was elevated in nodules formed with a Kantigen
deficient rhizobium mutant, but not in response to purified Nod factors. The putative
Mtchit4 chitinase is closely related to pathogenesis-related class IV chitinases from other
plants, and it is assumed that Mtchit4 is a pathogenesis related protein. This is supported by
an additional study that revealed a low overall expression of Mtchit4 throughout the plant,
independent of the plant’s symbiotic status, and an in silico analysis of the Mtchit4 promoter
sequence, which contains a variety of putative cis-elements related to plant defence.
The expression of two genes encoding class I chitinases, Mtchit1a and Mtchit1c, were
compared to the expression of Mtchit4 in leaves, roots and flowers and after infection with a
mycorrhizal fungus. In contrast to the constitutively expressed Mtchit1c, the expression of
Mtchit1a was similar in leaves or roots but low in flowers. Both chitinase genes were not
affected by mycorrhizal infection. The differential expression patterns, together with
sequence data and in silico promoter analyses, suggest that these genes encode
pathogenesis related chitinases, that are specifically regulated in response to infection by
pathogenic fungi.
Mtchit3-3 is a class III chitinase gene that was specifically induced in mycorrhizal roots. The
Mtchit3-3 promoter directs reporter gene expression to arbuscule containing cells, which is
consistent with mycorrhiza-related elements found in the promoter sequence. Disruption of
the Mtchit3-3 gene expression in root organ cultures stimulated spore germination of
mycorrhizal fungi and in one fungal strain resulted in a higher probability of root colonization
and spore formation. No effect on the abundance of arbuscules within colonized roots
became apparent. Mtchit3-3-GFP fusion constructs revealed that the putative signal peptide
could direct the Mtchit3-3 protein to the apoplast. It is suggested that the chitinase Mtchit3-3
is enzymatically active and might act on chitin in the fungal cell wall or fungal chitin-related
signals during the symbiosis and it may be involved in communication processes between
plant and AM.
The class III chitinase genes Mtchit3-1 and Mtchit3-4 are induced in response to infection by
pathogenic fungi in roots of M. truncatula. Mtchit3-4, but not Mtchit3-1, was also slightly
induced during mycorrhiza formation. According to their gene and protein structures in
comparison to chitinases in other plant species and additional in silico promoter analyses, it
is proposed that Mtchit3-1 is a pathogenesis related chitinase while Mtchit3-4 may be related
in a general way to fungal infections.
The functionality of the arbuscular mycorrhizal symbiosis was measured by comparing the
plant’s nutritional status and growth response of three mycorrhizal fungi from two different
phylogenetic taxa, namely Glomus intraradices, Glomus mosseae and Scutellospora
castanea. Mycorrhiza formation enhanced biomass accumulation and nutritional status of the
plants in each case, although the response was not related to the colonization degree.
To supplement the expression data of chitinase genes in relation to different fungal
infections, the expression was measured in the roots of M. truncatula plants colonized with
the three AMF. In addition, a selected set of other symbiosis related genes were tested that
responded differently to the AMF colonization. It can be concluded that a subset of the genes
that respond to colonization by the two Glomus species also responded to at least one
fungus from the Gigasporaceae. These data indicate that different genes showing arbusculespecific
gene expression in colonized roots are regulated by different mechanisms,
depending on the fungal partner
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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