Project description:Deadwood plays a crucial role in forest ecosystems, but we have limited information about the specific fungal taxa and extracellular lignocellulolytic enzymes that are actively involved in the decomposition process in situ. To investigate this, we studied the fungal metaproteome of twelve deadwood tree species in a replicated, eight-year experiment. Key fungi observed included genera of white-rot fungi (Basidiomycota, e.g. Armillaria, Hypholoma, Mycena, Ischnoderma, Resinicium), brown-rot fungi (Basidiomycota, e.g. Fomitopsis, Antrodia), diverse Ascomycota including xylariacous soft-rot fungi (e.g. Xylaria, Annulohypoxylon, Nemania) and various wood-associated endophytes and saprotrophs (Ascocoryne, Trichoderma, Talaromyces). These fungi used a whole range of extracellular lignocellulolytic enzymes, such as peroxidases, peroxide-producing enzymes, laccases, cellulases, glucosidases, hemicellulases (xylanases) and lytic polysaccharide monooxygenases (LPMOs). Both the fungi and enzymes were tree-specific, with specialists and generalists being distinguished by network analysis. The extracellular enzymatic system was highly redundant, with many enzyme classes of different origins present simultaneously in all decaying logs. Strong correlations were found between peroxide-producing enzymes (oxidases) and peroxidases as well as LPMOs, and between ligninolytic, cellulolytic and hemicellulolytic enzymes. The overall protein abundance of lignocellulolytic enzymes was reduced by up to -30% in gymnosperm logs compared to angiosperm logs, and gymnosperms lacked ascomycetous enzymes, which may have contributed to the lower decomposition of gymnosperm wood. In summary, we have obtained a comprehensive and detailed insight into the enzymatic machinery of wood-inhabiting fungi in several temperate forest tree species, which can help to improve our understanding of the complex ecological processes in forest ecosystems.
Project description:Many trees form ectomycorrhizal symbiosis with fungi. During symbiosis, the tree roots supply sugar to the fungi in exchange for nitrogen, and this process is critical for the nitrogen and carbon cycles in forest ecosystems. However, the extents to which ectomycorrhizal fungi can liberate nitrogen and modify the soil organic matter and the mechanisms by which they do so remain unclear since they have lost many enzymes for litter decomposition that were present in their free-living, saprotrophic ancestors. Using time-series spectroscopy and transcriptomics, we examined the ability of two ectomycorrhizal fungi from two independently evolved ectomycorrhizal lineages to mobilize soil organic nitrogen. Both species oxidized the organic matter and accessed the organic nitrogen. The expression of those events was controlled by the availability of glucose and inorganic nitrogen. Despite those similarities, the decomposition mechanisms, including the type of genes involved as well as the patterns of their expression, differed markedly between the two species. Our results suggest that in agreement with their diverse evolutionary origins, ectomycorrhizal fungi use different decomposition mechanisms to access organic nitrogen entrapped in soil organic matter. The timing and magnitude of the expression of the decomposition activity can be controlled by the below-ground nitrogen quality and the above-ground carbon supply.
Project description:Trees establish a symbiotic relationship with specialized soil fungi, called ectomycorrhizae, which is essential for nutrition, growth and health of temperate forest ecosystems. Understanding the mechanisms governing the establishment and functioning of ectomycorrhiza is important because of the role of forests in sequestering CO2 and also to develop ways to optimize tree productivity and sustainability. Here, we investigated the response of an oak species to ectomycorrhiza formation using a two dimensional differential in gel electrophoresis (2D-DIGE) and MALDI-TOF/TOF mass spectrometry proteomics approach. At the root level, changes in the abundance of 34 unique oak proteins were detected and revealed proteins involved in carbon and energy metabolism, protein processing and degradation, response to oxidative stress, lipid metabolism/transport, nitrogen and phosphorous assimilation and cell wall modification. Proteins supporting the importance of the secretory pathway functioning, in particular of the endoplasmic reticulum, during ectomycorrhiza functioning were identified. These proteins were identified as components of the endoplasmic reticulum folding/chaperoning machinery and proteins involved in the ER quality control system. This study constitutes an important contribution for the understanding of the mechanisms underlying the response of plants to ectomycorrhizal symbiosis establishment.
Project description:Arsenic (As) bioavailability in the rice rhizosphere is influenced by many microbial interactions, particularly by metal-transforming functional groups at the root-soil interface. This study was conducted to examine As-transforming microbes and As-speciation in the rice rhizosphere compartments, in response to two different water management practices (continuous and intermittently flooded), established on fields with high to low soil-As concentration. Microbial functional gene composition in the rhizosphere and root-plaque compartments were characterized using the GeoChip 4.0 microarray. Arsenic speciation and concentrations were analyzed in the rhizosphere soil, root-plaque, porewater and grain samples. Results indicated that intermittent flooding significantly altered As-speciation in the rhizosphere, and reduced methyl-As and AsIII concentrations in the pore water, root-plaque and rice grain. Ordination and taxonomic analysis of detected gene-probes indicated that root-plaque and rhizosphere assembled significantly different metal-transforming functional groups. Taxonomic non-redundancy was evident, suggesting that As-reduction, -oxidation and -methylation processes were performed by different microbial groups. As-transformation was coupled to different biogeochemical cycling processes establishing functional non-redundancy of rice-rhizosphere microbiome in response to both rhizosphere compartmentalization and experimental treatments. This study confirmed diverse As-biotransformation at root-soil interface and provided novel insights on their responses to water management, which can be applied for mitigating As-bioavailability and accumulation in rice grains.
Project description:The decomposition of large woody material is an important process in forest carbon cycling and nutrient release. Cord-forming saprotrophic basidiomycete fungi create non-resource limited mycelial networks between decomposing branches, logs and tree stumps on the forest floor where colonisation of new resource is often associated with the replacement of incumbent decay communities. Cord-forming species often dominate competition hierarchies in controlled paired antagonism experiments and have been shown to translocate resource to support colonisation and produce inhibitory metabolites. To date, antagonism experiments have mostly placed competing fungi in direct contact, while in nature cord-forming saprobes encounter colonised wood as mycelia in a network. Here we used soil-based microcosms that allowed foraging cord-forming Hypholoma fasciculare to encounter a wood block colonised by Trametes versicolor and conducted transcriptomic and proteomic analysis of the interaction. Cellular processes and metabolic responses to the competitive interaction were identified, where protein turnover featured strongly for both species. H. fasciculare demonstrated an exploitative profile with increased transcription of enzymes that targeted carbohydrate polymers of the substrate and in RNA and ribosome processing. T. versicolor showed a shift in signalling, energy generation and amino acid metabolism. Putative genes involved in secondary metabolite production were identified in both species. This study highlights the importance of ecologically-relevant experimental design when considering complex processes such as community development during wood decomposition
Project description:Mycorrhizae, symbiotic interactions between soil fungi and tree roots, are ubiquitous in terrestrial ecosystems. The fungi contribute phosphorous, nitrogen and mobilized nutrients from organic matter in the soil and in return the fungus receives photosynthetically-derived carbohydrates. This union of plant and fungal metabolisms is the mycorrhizal metabolome. Understanding this symbiotic relationship at a molecular level provides important contributions to the understanding of forest ecosystems and global carbon cycling. We generated next generation short-read transcriptomic sequencing data from fully-formed ectomycorrhizae between Laccaria bicolor and aspen (Populus tremuloides) roots. The transcriptomic data was used to identify statistically significantly expressed gene models using a bootstrap-style approach, and these expressed genes were mapped to specific metabolic pathways. Integration of expressed genes that code for metabolic enzymes and the set of expressed membrane transporters generates a predictive model of the ectomycorrhizal metabolome. Results indicate the specific compounds glycine, glutamate, and allantoin are synthesized by L. bicolor and that these compounds or their metabolites may be used for the benefit of aspen in exchange for the photosynthetically-derived sugars fructose and glucose.The analysis illustrates an approach to generate testable biological hypotheses to investigate the complex molecular interactions that drive ectomycorrhizal symbiosis. These models are consistent with experimental environmental data and provide insight into the molecular exchange processes for organisms in this complex ecosystem. The method used here for predicting metabolomic models of mycorrhizal systems from deep RNA sequencing data can be generalized and is broadly applicable to transcriptomic data derived from complex systems. Fully formed L.bicolor::P.trichocapra mycorrhizae in duplicate
Project description:MicroRNAs (miRNAs) are a class of endogenous small RNAs that play important roles in growth, development, and environmental stress response processes in plants. Ulmus pumila is a typical deciduous broadleaved tree species of north temperate, and is widely distributed in central and northern Asia, which has important economic and ecological value. With the spread and aggravate of soil salinisation, salt stress has become a major abiotic stress that highly affects the normal growth and development of U. pumila. However, to date, no investigation into the influence of salt stress on U. pumila miRNAs has been reported. To identify miRNAs and predict their target mRNA genes under salt stress, three small RNA libraries were generated and sequenced from CK (without salt stress), LSS (light salt stress for a short time) and MSL (medium-heavy salt stress for a long time) roots of U. pumila seedlings. Through integrative analysis, 245 conserved miRNAs representing 30 families and 64 novel miRNAs were identified, of which 89 exhibited altered expression level under salt stress, and 232 potential targets for the miRNAs were predicted and annotated in U. pumila. The expressions of six differentially expressed miRNAs were validated by qRT-PCR. These salt responsive miRNAs may play crucial roles in U. pumila defense against salt stress, and our miRNA data provides valuable information regarding further functional analysis of miRNAs involved in salt tolerance of U. pumila and other forest tree species.
2018-12-31 | GSE84937 | GEO
Project description:Tree mycorrhizal association and soil pathogenic fungi mediate density- dependent survival of trees in a temperate forest
Project description:Rhizosphere is a complex system of interactions between plant roots, bacteria, fungi and animals, where the release of plant root exudates stimulates bacterial density and diversity. However, the majority of the bacteria in soil results to be unculturable but active. The aim of the present work was to characterize the microbial community associated to the root of V. vinifera cv. Pinot Noir not only under a taxonomic perspective, but also under a functional point of view, using a metaproteome approach. Our results underlined the difference between the metagenomic and metaproteomic approach and the large potentiality of proteomics in describing the environmental bacterial community and its activity. In fact, by this approach, that allows to investigate the mechanisms occurring in the rhizosphere, we showed that bacteria belonging to Streptomyces, Bacillus and Pseudomonas genera are the most active in protein expression. In the rhizosphere, the identified genera were involved mainly in phosphorus and nitrogen soil metabolism.