Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Network analysis of wood properties, gene expression levels and genotypes of natural Populus trichocarpa accessions

ABSTRACT: High-throughput approaches have been widely applied to elucidate the genetic underpinnings of industrially important wood properties. Each single wood trait was found to be highly polygenic in its nature. However, gene hierarchies need to be assessed with the most important gene variants controlling a specific trait within the complex network of interacting secondary cell wall characteristics that defines the overall wood phenotype. We tested the available genetic and genomic information in an integrative approach to effectively predict wood properties in Populus trichocarpa.Nine-yr-old natural P. trichocarpa trees including accessions with high contrasts in six traits related to wood chemistry and ultrastructure were profiled for gene expression on 49K Nimblegen array elements and for 28,831 polymorphic SNPs. Pre-selected transcripts and SNPs with high statistical dependency on the phenotypic trait were used in a Bayesian network learning procedure with stepwise K2 algorithm to infer phenotype-centric networks. Transcripts were pre-selected at much lower logBF threshold than SNPs and were not accommodated in the networks. Complexity of phenotype-centric networks with 100% predictive accuracy ranged from 7 (glucose) to 39 SNPs (alpha-cellulose). Pleiotropic gene actions were accommodated in genetic networks of correlated traits; such gene variants help to understand independent evolution of trait values, and they represent new tools to support the maximization of correlated response to selection. Developing xylem harvested at breast height from the north side of each tree stem from 17 genotypes with two biological replicates and from two additional genotypes without a second replicate previously identified as most extreme phenotypes in six wood traits was individually profiled for transcriptome analysis totaling 36 hybridizations to three NimbleGen 12-plex poplar arrays.

ORGANISM(S): Populus trichocarpa

SUBMITTER: Ilga Porth

PROVIDER: E-GEOD-44606 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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.

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:Wood-degrading brown rot fungi are essential recyclers of plant biomass in forest ecosystems. Their efficient cellulolytic systems, which have potential biotechnological applications, apparently depend on a combination of two mechanisms: lignocellulose oxidation by reactive oxygen species (ROS) and polysaccharide hydrolysis by a limited set of glycoside hydrolases (GHs). Given that ROS are strongly oxidizing and non-selective, these two steps are likely segregated. A common hypothesis has been that brown rot fungi use a concentration gradient of chelated metal ions to confine ROS generation inside wood cell walls before enzymes can infiltrate. We examined an alternative: that lignocellulose-oxidation (LOX) components involved in ROS production are differentially expressed by brown rot fungi ahead of GH components. We used spatial mapping to resolve a temporal sequence in Postia placenta, sectioning thin wood wafers colonized directionally. Among sections, we measured gene expression by whole transcriptome sequencing (RNAseq) and assayed relevant enzyme activities. We found a marked pattern of LOX upregulation in a narrow (5-mm; 48-hr) zone at the hyphal front, which included many genes likely involved in ROS generation. Upregulation of GH5 endoglucanases and many other GHs clearly occurred later, behind the hyphal front, with notable exceptions of two likely expansins and a GH28 pectinase. Our results support a staggered mechanism for brown rot that is controlled by differential expression rather than microenvironmental gradients. This mechanism likely results in an oxidative pretreatment of lignocellulose, possibly facilitated by expansin- and pectinase-assisted cell wall swelling, before cellulases and hemicellulases are deployed for polysaccharide depolymerization. We sequenced mRNA from 9 Postia placenta samples taken from 3 wood sections of wafer design, with 3 bioreplicates for each wood section, to compare the gene expression during brown rot processes. Three wood sections of the wafer are representing early to late decay stages.

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Network analysis of wood properties, gene expression levels and genotypes of natural Populus trichocarpa accessions

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