Basidiomycota et Ascomycota
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Dossier > Les lichens : témoins de la pollution atmosphérique

Dossier > Les lichens : témoins de la pollution atmosphérique | Basidiomycota et Ascomycota | Scoop.it
Les lichens sont des organismes particuliers qui peuvent nous renseigner sur la qualité de l'air. La dégradation environnementale est une question d'actualité liée aux nombreuses activités...
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Les lichens sont issus d’une symbiose entre un champignon appelé mycobionte ou mycosymbiote, en majorité un Ascomycète, et une algue appelée photobionte ou photosymbiote. Dans 90 % des cas, le photobionte est une algue verte (chlorolichens), alors qu’il s’agit d’unecyanobactérie (cyanolichens) dans les 10 % restants. Ces deux partenaires sont indispensables au bon fonctionnement de leur association. L’algue synthétise la matière organique à partir du dioxyde de carbone (CO2) de l’air et du rayonnement solaire(photosynthèse). En contrepartie, le champignon prélève dans le milieu l’eau et les sels minéraux indispensables à la symbiose lichénique. Les éléments nutritifs n’étant pas puisés dans le substrat, les lichens ne sont donc pas néfastes au développement de l’arbre. Le partenaire fongique est également responsable de l’ancrage de la structure et protège l’association lichénique des rayonnementsultraviolets trop agressifs et de leurs possibles effets délétères.

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BioTechniques - How Ancient Sake Brewers Tamed a Fungus

BioTechniques - How Ancient Sake Brewers Tamed a Fungus | Basidiomycota et Ascomycota | Scoop.it
A comparative genetic study suggests that ancient sake brewers evolved a toxin-producing wild fungus into an alcohol producing by selecting desired genetic variants. 

In a paper published in the journal Current Biology, Vanderbilt researchers conducted a comparative genomic study of two closely related but very differently functioning fungi—the domesticated Aspergillus oryzae, which is used in sake production, and its wild and harmful relative Aspergillus flavus,which produces a powerful natural carcinogen called aflatoxin. In the end, the study highlights a major difference between the domestication of microbes and that of plants and animals.

“If you think of the classic case of domestication in plants and animals, they involved a lot of changes in morphology,” said Antonis Rokas, assistant professor of biological sciences at Vanderbilt University. “But, in fungi, what we’re seeing for the first time, is that almost entirely all the changes are changes in metabolism. So, there’s change in the physiology much more in microbes than in development.”

In the paper, Rokas and his team propose that a thousand years ago, A. oryzae was once a toxigenic microbe that more closely resembled A. flavus than today’s strains do. But that was before sake brewers began working with the fungus, turning A. oryzae into a cell factory to produce the enzymes and metabolites that are necessary to breakdown rice starch into sugar, which is then converted into alcohol by yeast. Through this artificial selection process, the genes involved in sugar production were upregulated, while the genes involved in the production of toxins were down-regulated.

“We think that part of the reason is that when you make sake, you actually have together both A. oryzae and Saccharomyces cerevisiae, the yeast that makes the alcohol. So, this coexistence has selected for A. oryzae to act friendly to the yeast,” said Rokas.

To perform the comparative genetic analysis, Rokas and his team collected genomic data that described the variation between both A. oryzae as well as its wild relative. They then collected gene expression data for some strains of both species when grown on rice. Finally, as part of their three-layer analysis, the lab collected proteomic data that showed the abundance of particular proteins during growth on rice again from each of the fungi.

“The main challenge was distilling down and trying to find the biology amidst these really huge data sets. We were dealing with gigabytes of data, but we’re lucky enough to have a super computer so the majority of the analysis was done there,” said Rokas.

To gain a better understanding about the process of microbial domestication, Rokas plans to study several other domesticated microbes. “In the way that we have a sort of consensus on the process of domestication of several different plants and animals, it would be nice to get the same kind of consensus or picture of how the domestication process works in microbes,” said Rokas.


Via Steve Marek
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David Hibbett at the 2012 DOE JGI Genomics of Energy & Environment Meeting

David Hibbett from Clark University on "Evolutionary Perspectives on Diversity of Lignocellulose Decay Mechanisms in Basidiomycetes" at the 7th Annual Genomi...
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CHARBON ET CHAMPIGNONS : L'absence de champignons capable de dégrader la lignine est à l'origine de la formation du charbon et du pétrole, notre source d'énergie principale. L'acquisition par certains champignons des enzymes nécessaires à la dégradation du bois il y a 300 millions d'années a causé l'arrêt de l'accumulation du pétrole et charbon. Une conférence en ANGLAIS des plus intéressantes de 30 min pour bien comprendre le rôle essentiel des champignons dans la formation de la nature telle que nous la connaissons aujourd'hui.

 

Voir : 

Science 29 June 2012: 
Vol. 336 no. 6089 pp. 1715-1719

http://www.sciencemag.org/content/336/6089/1715.short

 

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Mycoquébec - Le phénomène de la guttation chez les champignons,...

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Dating the Diversification of the Major Lineages of Ascomycota (Fungi)

Dating the Diversification of the Major Lineages of Ascomycota (Fungi) | Basidiomycota et Ascomycota | Scoop.it
Abstract

Establishing the dates for the origin and main diversification events in the phylogeny of Ascomycota is among the most crucial remaining goals in understanding the evolution of Fungi. There have been several analyses of divergence times in the fungal tree of life in the last two decades, but most have yielded contrasting results for the origin of the major lineages. Moreover, very few studies have provided temporal estimates for a large set of clades within Ascomycota. We performed molecular dating to estimate the divergence times of most of the major groups of Ascomycota. To account for paleontological uncertainty, we included alternative fossil constraints as different scenarios to enable a discussion of the effect of selection of fossils. We used data from 6 molecular markers and 121 extant taxa within Ascomycota. Our various ‘relaxed clock’ scenarios suggest that the origin and diversification of the Pezizomycotina occurred in the Cambrian. The main lineages of lichen–forming Ascomycota originated at least as early as the Carboniferous, with successive radiations in the Jurassic and Cretaceous generating the diversity of the main modern groups. Our study provides new information about the timing of the main diversification events in Ascomycota, including estimates for classes, orders and families of both lichenized and non–lichenized Ascomycota, many of which had not been previously dated.

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Les champignons sortent du bois

Les champignons sortent du bois | Basidiomycota et Ascomycota | Scoop.it

La génomique à grande échelle décloisonne la classification des basidiomycètes et ouvre des perspectives pour les biocarburants.
Les champignons constituent un règne du vivant encore peu exploré malgré son potentiel immense.


Via AgroParisTech DOC IST, Isabelle Pélissié
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PNAS  111: 9923-9928, 2014 

http://www.pnas.org/content/111/27/9923

 

Abstract

Basidiomycota (basidiomycetes) make up 32% of the described fungi and include most wood-decaying species, as well as pathogens and mutualistic symbionts. Wood-decaying basidiomycetes have typically been classified as either white rot or brown rot, based on the ability (in white rot only) to degrade lignin along with cellulose and hemicellulose. Prior genomic comparisons suggested that the two decay modes can be distinguished based on the presence or absence of ligninolytic class II peroxidases (PODs), as well as the abundance of enzymes acting directly on crystalline cellulose (reduced in brown rot). To assess the generality of the white-rot/brown-rot classification paradigm, we compared the genomes of 33 basidiomycetes, including four newly sequenced wood decayers, and performed phylogenetically informed principal-components analysis (PCA) of a broad range of gene families encoding plant biomass-degrading enzymes. The newly sequenced Botryobasidium botryosum and Jaapia argillacea genomes lack PODs but possess diverse enzymes acting on crystalline cellulose, and they group close to the model white-rot species Phanerochaete chrysosporium in the PCA. Furthermore, laboratory assays showed that both B. botryosum and J. argillaceacan degrade all polymeric components of woody plant cell walls, a characteristic of white rot. We also found expansions in reducing polyketide synthase genes specific to the brown-rot fungi. Our results suggest a continuum rather than a dichotomy between the white-rot and brown-rot modes of wood decay. A more nuanced categorization of rot types is needed, based on an improved understanding of the genomics and biochemistry of wood decay.

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