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Regulation of gene expression during the onset of ligninolytic oxidation by Phanerochaete chrysosporium on colonized wood

ABSTRACT: The biodegradation of lignocellulose requires the disruption of its lignin, which shields the metabolically assimilable polysaccharides in this recalcitrant natural composite. Although a variety of microorganisms can attack lignocellulose, white rot basidiomycetes are uniquely efficient at this process, cleaving the recalcitrant intermonomer linkages of lignin via extracellular oxidative mechanisms and mineralizing many of the resulting fragments to carbon dioxide via intracellular processes. Considerable progress has been made in understanding this process in the model white rot fungus Phanerochaete chrysosporium, which expresses important components of its ligninolytic system in response to nutrient limitation, as part of its secondary metabolism. Biochemical and genetic evidence point to an important role in P. chrysosporium for secreted lignin peroxidases (LiPs), manganese peroxidases (MnPs), and H2O2-producing oxidases, which are thought to work together to cleave lignin into low molecular weight fragments. However, many aspects of ligninolysis by P. chrysosporium remain poorly understood. Although a definitive picture of the entire ligninolytic system in P. chrysosporium is not yet attainable, transcriptome analyses of the fungus grown on wood can provide useful clues. With the advent of the initial genome assembly and annotations (v1.0 and v2.1), microarray-based transcriptome analysis allowed examination of transcript levels of P. chrysosporium genes when grown in ball-milled wood and in defined growth media. This approach provided useful insights but was limited to 10048 v2.1 targets and complicated by the unpredictable manner in which the fungus responds to unnatural carbon sources in submerged basal salts media. A complete, fully coordinated ligninolytic system is likely not expressed by P. chrysosporium on ball-milled wood, because a potential route for regulatory feedback has been eliminated: the cellulose and hemicellulose in this substrate is readily accessible to enzymes, and thus ligninolysis is not essential for growth. An alternative approach is to compare levels of gene expression just before and after the onset of secondary metabolism and extracellular substrate oxidation by P. chrysosporium as it utilizes solid wood as its carbon source. If this can be done, and decay of the substrate is also confirmed, then the genes undergoing marked changes in expression during the metabolic transition can be identified with greater confidence. Although not all such genes are expected to have roles in biodegradation, this strategy may identify interesting candidates for future investigation. Here we report RNAseq-based transcriptomes to characterize changes in gene expression that occur during the transition to ligninolytic metabolism.

ORGANISM(S): Phanerodontia chrysosporium

PROVIDER: GSE69461 | GEO | 2015/09/16

SECONDARY ACCESSION(S): PRJNA285669

REPOSITORIES: GEO

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Project description:The biodegradation of lignocellulose requires the disruption of its lignin, which shields the metabolically assimilable polysaccharides in this recalcitrant natural composite. Although a variety of microorganisms can attack lignocellulose, white rot basidiomycetes are uniquely efficient at this process, cleaving the recalcitrant intermonomer linkages of lignin via extracellular oxidative mechanisms and mineralizing many of the resulting fragments to carbon dioxide via intracellular processes. Considerable progress has been made in understanding this process in the model white rot fungus Phanerochaete chrysosporium, which expresses important components of its ligninolytic system in response to nutrient limitation, as part of its secondary metabolism. Biochemical and genetic evidence point to an important role in P. chrysosporium for secreted lignin peroxidases (LiPs), manganese peroxidases (MnPs), and H2O2-producing oxidases, which are thought to work together to cleave lignin into low molecular weight fragments. However, many aspects of ligninolysis by P. chrysosporium remain poorly understood. Although a definitive picture of the entire ligninolytic system in P. chrysosporium is not yet attainable, transcriptome analyses of the fungus grown on wood can provide useful clues. With the advent of the initial genome assembly and annotations (v1.0 and v2.1), microarray-based transcriptome analysis allowed examination of transcript levels of P. chrysosporium genes when grown in ball-milled wood and in defined growth media. This approach provided useful insights but was limited to 10048 v2.1 targets and complicated by the unpredictable manner in which the fungus responds to unnatural carbon sources in submerged basal salts media. A complete, fully coordinated ligninolytic system is likely not expressed by P. chrysosporium on ball-milled wood, because a potential route for regulatory feedback has been eliminated: the cellulose and hemicellulose in this substrate is readily accessible to enzymes, and thus ligninolysis is not essential for growth. An alternative approach is to compare levels of gene expression just before and after the onset of secondary metabolism and extracellular substrate oxidation by P. chrysosporium as it utilizes solid wood as its carbon source. If this can be done, and decay of the substrate is also confirmed, then the genes undergoing marked changes in expression during the metabolic transition can be identified with greater confidence. Although not all such genes are expected to have roles in biodegradation, this strategy may identify interesting candidates for future investigation. Here we report RNAseq-based transcriptomes to characterize changes in gene expression that occur during the transition to ligninolytic metabolism. Phanerochaete chrysosporium was inoculated onto thin sections of wood. RNA was purified from colonized material after 40 and 96 hours. Single read 100 bp Illumina runs were performed.

Project description:Using whole genome microarrays based on the annotated genomes of Phanerochaete chrysosporium, we monitored the changes in its transcriptomes relevant to cell wall degradation during growth on three chemically distinct Populus trichocarpa (poplar) wood substrates. Results of this study are sumbitted for review in Biotechnology for Biofuels From a data set of 10004 unique gene models, each NimbleGen (Madison, WI) array targeted 9959 genes and featured 12 unique 60mers per gene, all in triplicate. RNA and protein were obtained from P. chrysosporium strain RP-78 (USDA Forest Mycology Center, Forest Products Laboratory, Madison WI) grown in malt extract agar for 10 days prior to inoculation with wood wafers. Three poplar wood substrates with distinct cell wall chemical properties were selected from several hundred 4-year old Populus trichocarpa trees grown in a common garden field trial at the University of British Columbia (Canada). We selected three poplar genotypes based on cell wall chemical traits. Substrate A corresponds to a genotype with a higher than average lignin content and lower that average glucose content; Substrate B, a lower than average lignin content and higher that average glucose content; Substrate C lignin and glucose contents are near the population average. Poplar wood stems were cut into 0.5 mm wafers on a microtome, sterilized for 20 min at 121°C, dried at 50°C overnight, and cooled to room temperature. The specimens were then inoculated in Petri dishes with actively growing mycelia. Approximately 5 g of wood wafers were placed in each Petri dish (exact weights were recorded), sealed and incubated at 22°C and 70 ± 5% relative humidity for 10, 20 or 30 days. For RNA, the degraded wafers were removed from the Petri dishes, immediately snap-frozen in liquid nitrogen and stored at -80°C for later use. Total RNA was converted to Cy3 labelled cDNA, hybridized to microarrays and scanned as previously described by Vanden Wymelenberg et al 2010 (Appl Enviro Microbiol 76:3599-3610).The 24 arrays per fungal species were scanned and data extracted using NimbleScan v.2.4. The raw data was loaded into GeneSpring, where the intensities were converted to log2 and quantile normalized, and all probes per gene averaged. This data was then exported and further analyzed in R. For substrates “A” and “B”, three replicates were used for each wood substrate/fungus and incubation period combination. For substrate “C” only 2 biological replicates were employed.

Project description:Fomitiporia mediterranea (Fmed) is one of the main fungal species found in grapevine wood rot, also called “amadou”, one of the most typical symptoms of grapevine trunk disease Esca. This fungus is functionally classified as a white-rot, able to degrade all wood structure polymers, i.e., hemicelluloses, cellulose, and the most recalcitrant component, lignin. Specific enzymes are secreted by the fungus to degrade those components, namely carbohydrate active enzymes for hemicelluloses and cellulose, which can be highly specific for given polysaccharide, and peroxidases, which enable white-rot to degrade lignin, with specificities relating to lignin composition as well. Furthermore, besides polymers, a highly diverse set of metabolites often associated with antifungal activities is found in wood, this set differing among the various wood species. Wood decayers possess the ability to detoxify these specific extractives and this ability could reflect the adaptation of these fungi to their specific environment. The aim of this study is to better understand the molecular mechanisms used by Fmed to degrade wood structure, and in particular its potential adaptation to grapevine wood. To do so, Fmed was cultivated on sawdust from different origins: grapevine, beech, and spruce. Carbon mineralization rate, mass loss, wood structure polymers contents, targeted metabolites and secreted proteins were measured. We used the well-known white-rot model Trametes versicolor for comparison. Whereas no significant degradation was observed with spruce, a higher mass loss was measured on Fmed grapevine culture compared to beech culture. Moreover, on both substrates, a simultaneous degradation pattern and the degradation of wood extractives were demonstrated, and proteomic analyses identified a relative overproduction of oxidoreductases involved in lignin and extractive degradation on grapevine cultures, and only few differences in carbohydrate active enzymes. These results could explain at least partially the adaptation of Fmed to grapevine wood structural composition compared to other wood species and suggest that other biotic and abiotic factors should be considered to fully understand the potential adaptation of Fmed to its ecological niche.

Project description:Using whole genome microarrays based on the annotated genomes of Postia placenta, we monitored the changes in its transcriptomes relevant to cell wall degradation during growth on three chemically distinct Populus trichocarpa (poplar) wood substrates. The research goal is to identtify genes essential for cellulose depolymerization. From a data set of 12438 unique gene models, each NimbleGen (Madison, WI) array targeted 9959 genes and featured 10 unique 60mers per gene, all in triplicate. RNA and protein were obtained from P. placenta strain MAD-698-R (USDA Forest Mycology Center, Forest Products Laboratory, Madison WI) grown in malt extract agar for 10 days prior to inoculation with wood wafers. Three poplar wood substrates with distinct cell wall chemical properties were selected from several hundred 4-year old poplar (Populus trichocarpa) trees grown in a common garden field trial at the University of British Columbia (Canada). We selected three poplar genotypes based on cell wall chemical traits. Substrate A corresponds to a genotype with a higher than average lignin content and lower that average glucose content; Substrate B, a lower than average lignin content and higher that average glucose content; Substrate C lignin and glucose contents are near the population average. Poplar wood stems were cut into 0.5 mm wafers on a microtome, sterilized for 20 min at 121°C, dried at 50°C overnight, and cooled to room temperature. The specimens were then inoculated in Petri dishes with actively growing mycelia. Approximately 5 g of wood wafers were placed in each Petri dish (exact weights were recorded), sealed and incubated at 22°C and 70 ± 5% relative humidity for 10, 20 or 30 days. For RNA, the degraded wafers were removed from the Petri dishes, immediately snap-frozen in liquid nitrogen and stored at -80°C for later use. Total RNA was converted to Cy3 labelled cDNA, hybridized to microarrays and scanned as previously described by Vanden Wymelenberg et al 2010 (Appl Enviro Microbiol 76:3599-3610).The 24 arrays per fungal species were scanned and data extracted using NimbleScan v.2.4. The raw data was loaded into GeneSpring, where the intensities were converted to log2 and quantile normalized, and all probes per gene averaged. This data was then exported and further analyzed in R. For substrates “A” and “B”, three replicates were used for each wood substrate/fungus and incubation period combination. For substrate “C” only 2 biological replicates were employed.

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Regulation of gene expression during the onset of ligninolytic oxidation by Phanerochaete chrysosporium on colonized wood

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