Structural and enzymatic insights into Lambda glutathione transferases from Populus trichocarpa, monomeric enzymes constituting an early divergent class specific to terrestrial plants
http://www.biochemj.org/bj/imps/abs/BJ20140390.htm
http://www.biochemj.org/bj/imps/abs/BJ20140390.htm
La campagne de recrutement des ATER 2014-2015 est lancée.
Elle se termine le 25 mai à minuit.
Les candidats doivent postuler sur GALAXIE par l’application ALTAIR
Ils recevront un identifiant et un mot de passe pour pouvoir déposer leur dossier de candidature sur l’application Esup-Dematec
The defense will be held the 28th May 2014 at 9H00 in Amphitheater 7, Faculté des Sciences, Boulevard des Aiguillettes, Vandoeuvre
Title: Bacterial-fungal interactions in wood decay: from wood physicochemical properties to taxonomic and functional diversity of Phanerochaete chrysosporium-associated bacterial communities
Wood decomposition is an important process in forest ecosystems in terms of their carbon and nutrient cycles. In temperate forests, saprotrophic basidiomycetes such as white-rot fungi are the main wood decomposers. While they have been less studied, bacterial communities also colonise decaying wood and coexist with these fungal communities. Although the impact of bacterial-fungal interactions on niche functioning has been highlighted in a wide range of environments, little is known about their role in wood decay. Based on microcosm experiments and using a culture-independent approach, we showed that the presence of the white-rot fungus Phanerochaete chrysosporium significantly modified the structure and diversity of the bacterial communities associated with the degradation of beech wood (Fagus sylvatica). Using a culture-dependent approach, it was confirmed that in the presence of the fungus the mycosphere effect resulted in increased bacterial abundance and modified the functional diversity of the fungal-associated bacterial communities. Lastly, a polyphasic approach simultaneously analysing wood physicochemical properties and extracellular enzyme activities was developed. This approach revealed that P. chrysosporium associated with a bacterial community isolated from its mycosphere was more efficient in degrading wood compared to the fungus on its own, highlighting for the first time synergistic bacterial-fungal interactions in decaying wood.
Keywords: wood decomposition, bacterial-fungal interactions, mycosphere effect, bacterial diversity, Phanerochaete chrysosporium, Fagus sylvatica, white rot.
Dans les écosystèmes forestiers, la décomposition du bois est un processus majeur, notamment impliqué dans le cycle du carbone et des nutriments. Les champignons basidiomycètes saprotrophes, incluant les pourritures blanches, sont les principaux agents de cette décomposition dans les forêts tempérées. Bien que peu étudiées, des communautés bactériennes sont également présentes dans le bois en décomposition et cohabitent avec ces communautés fongiques. L’impact des interactions bactéries-champignons sur le fonctionnement d’une niche écologique a été décrit dans de nombreuxenvironnements. Cependant, très peu de choses sont connues sur leur rôle dans le processus de décomposition du bois. A partir d’expériences en microcosme et en utilisantune approche non cultivable, il a été démontré que la présence du champignonPhanerochaete chrysosporiuminfluençait significativement la structureet la diversité des communautés bactériennes associées au processus de décomposition du hêtre (Fagus sylvatica). Par une approche cultivable, cet effet mycosphère aété confirmé, se traduisant par une augmentation de la concentration des communautés bactériennes en présence du champignonainsi que par une modification de la diversité fonctionnelle des communautés bactériennes associées au champignon. Enfin, une approche polyphasique a été développée,combinant l’analyse des propriétés physico-chimiques du bois et des activités enzymatiques extracellulaires. Ces derniers résultatsont révélé que l’association de P. chrysosporium avec une communauté bactérienne issue de la mycosphère de ce dernier aboutissait à une dégradation plus importante du matériau bois par rapport à la dégradation par le champignon seul, indiquant pour la première fois une interaction bactéries-champignon synergique dans le bois en décomposition.
Mots-clefs : décomposition du bois, interactions bactéries-champignons, effet mycosphère, diversité bactérienne, Phanerochaete chrysosporium, Fagus sylvatica, pourriture blanche.
Orchid mycorrhiza has been often interpreted as an antagonistic relationship. Our data on mycorrhizal protocorms do not support this view as plant defence genes were not induced, whereas some nodulin-like genes were significantly up-regulated.
Orchids fully depend on symbiotic interactions with specific soil fungi for seed germination and early development. Germinated seeds give rise to a protocorm, a heterotrophic organ that acquires nutrients, including organic carbon, from the mycorrhizal partner. It has long been debated if this interaction is mutualistic or antagonistic. To investigate the molecular bases of the orchid response to mycorrhizal invasion, we developed a symbiotic in vitro system between Serapias vomeracea, a Mediterranean green meadow orchid, and the rhizoctonia-like fungus Tulasnella calospora. 454 pyrosequencing was used to generate an inventory of plant and fungal genes expressed in mycorrhizal protocorms, and plant genes could be reliably identified with a customized bioinformatic pipeline. A small panel of plant genes was selected and expression was assessed by real-time quantitative PCR in mycorrhizal and non-mycorrhizal protocorm tissues. Among these genes were some markers of mutualistic (e.g. nodulins) as well as antagonistic (e.g. pathogenesis-related and wound/stress-induced) genes. None of the pathogenesis or wound/stress-related genes were significantly up-regulated in mycorrhizal tissues, suggesting that fungal colonization does not trigger strong plant defence responses. In addition, the highest expression fold change in mycorrhizal tissues was found for a nodulin-like gene similar to the plastocyanin domain-containing ENOD55. Another nodulin-like gene significantly more expressed in the symbiotic tissues of mycorrhizal protocorms was similar to a sugar transporter of the SWEET family. Two genes coding for mannose-binding lectins were significantly up-regulated in the presence of the mycorrhizal fungus, but their role in the symbiosis is unclear.
Quels mystères, quelles ressources encore inexploitées cachent les champignons ? Un ouvrage original qui explique le fonctionnement complexe des champignons et dévoile leurs surprenantes vertus, les dégâts causés et leur omniprésence dans notre vie quotidienne. Les champignons sont en effet utilisés en agroalimentaire, en médecine mais aussi pour l’agriculture et l’environnement.
Ectomycorrhizal Cortinarius species participate in enzymatic oxidation of humus in northern forest ecosystems
I Bödeker, KE Clemmensen, W Boer, F Martin, Å Olson, BD Lindahl. New Phytologist
Modeling climate impact on an emerging disease, the Phytophthora alni induced alder decline J Aguayo, F Elegbede, C Husson, FX Saintonge, B Marçais. Global Change Biology
Alder decline caused by Phytophthora alni is one of the most important emerging diseases in natural ecosystems in Europe, where it has threatened riparian ecosystems for the past 20 years. Environmental factors, such as mean site temperature and soil characteristics, play an important role in the occurrence of the disease. The objective of the present work was to model and forecast the effect of environment on the severity of alder Phytophthora outbreaks, and to determine whether recent climate change might explain the disease emergence. Two alder sites networks in NE and SW France were surveyed to assess the crown health of trees; the oomycete soil inoculum was also monitored in the NE network. The main factors explaining the temporal annual variation of alder crown decline or crown recovery were the mean previous winter and previous summer temperatures. Both low winter temperatures and high summer temperatures were unfavorable to the disease. Cold winters promoted tree recovery because of poor survival of the pathogen, while hot summer temperature limited the incidence of tree decline. An SIS model explaining the dynamics of the P. alni induced alder decline was developed using the data of the NE site network and validated using the SW site network. This model was then used to simulate the frequency of declining alder over time with historical climate data. The last 40 years’ weather conditions have been generally favorable to the establishment of the disease, indicating that others factors may be implicated in its emergence. The model, however, showed that the climate of SW France was much more favorable for the disease than that of the Northeast, because it seldom limited the overwintering of the pathogen. Depending on the European area, climate change could either enhance or decrease the severity of the alder decline.
Tuesday 15th of april 2014 – 1.30pm
Petr Baldrian (Laboratory of Environmental Microbiology, Prague, Rep Tchèque)
SE Elefsen, P Frey, H Sverrisson, JH Hallsson
European Journal of Plant Pathology, 1-12
The basidiomycete Melampsora larici-populina causes foliar rust on Populus species from the sections Aigeiros and Tacamahaca, causing reduction in biomass production and economic losses. In the present study, samples of Icelandic M. larici-populina were collected for analysis of genetic diversity and population structure. A total of 439 isolates, collected at 15 locations, and analysed using 22 microsatellite markers were compared to data from French M. larici-populina populations. Twenty-one of the loci analysed were polymorphic, with an average of 3.4 alleles per locus. The mean observed and expected heterozygosities for all populations were 0.35 and 0.38. Evidence was found for a substructure within the Icelandic population with three subpopulations being the most likely scenario with low levels of gene flow. The population structure seen here is most likely shaped by both isolation and genetic drift as well as repeated events of colonization. In the future it can therefore be expected that regional poplar rust genotypes in Iceland change by two different modes; on one hand by transport of spores within the country and on the other hand by repeated colonization events. The results reported here underline the importance of closely monitoring the development of fungal diseases in Iceland, and to carefully select for resistance in Icelandic plant breeding programs.