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. 2014 Dec 4;10(12):e1004759.
doi: 10.1371/journal.pgen.1004759. eCollection 2014 Dec.

Analysis of the Phlebiopsis Gigantea Genome, Transcriptome and Secretome Provides Insight Into Its Pioneer Colonization Strategies of Wood

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Free PMC article

Analysis of the Phlebiopsis Gigantea Genome, Transcriptome and Secretome Provides Insight Into Its Pioneer Colonization Strategies of Wood

Chiaki Hori et al. PLoS Genet. .
Free PMC article

Abstract

Collectively classified as white-rot fungi, certain basidiomycetes efficiently degrade the major structural polymers of wood cell walls. A small subset of these Agaricomycetes, exemplified by Phlebiopsis gigantea, is capable of colonizing freshly exposed conifer sapwood despite its high content of extractives, which retards the establishment of other fungal species. The mechanism(s) by which P. gigantea tolerates and metabolizes resinous compounds have not been explored. Here, we report the annotated P. gigantea genome and compare profiles of its transcriptome and secretome when cultured on fresh-cut versus solvent-extracted loblolly pine wood. The P. gigantea genome contains a conventional repertoire of hydrolase genes involved in cellulose/hemicellulose degradation, whose patterns of expression were relatively unperturbed by the absence of extractives. The expression of genes typically ascribed to lignin degradation was also largely unaffected. In contrast, genes likely involved in the transformation and detoxification of wood extractives were highly induced in its presence. Their products included an ABC transporter, lipases, cytochrome P450s, glutathione S-transferase and aldehyde dehydrogenase. Other regulated genes of unknown function and several constitutively expressed genes are also likely involved in P. gigantea's extractives metabolism. These results contribute to our fundamental understanding of pioneer colonization of conifer wood and provide insight into the diverse chemistries employed by fungi in carbon cycling processes.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Schematic representations of lignocellulose components in cell walls of pine wood.
Panel A: The extractives (long chain fatty acids, triglycerides, resin acids and terpenes) are found primarily in the resin ducts, but damage to pine wood causes the release of these compounds across wounded areas. Panel B: In tracheid cell walls, the amorphous, phenylpropanoid polymer lignin (brown) form a matrix around the more structured carbohydrate polymers, hemicellulose (yellow and green) and cellulose (blue).
Figure 2
Figure 2. Wood decay characteristics.
Comparative weight loss of parental strain 11061 and single basidiospore derivatives on colonized loblolly pine wood (Pinus taeda) wood wafers were determined after 4, 8 and 12 weeks incubation (bottom left panel) as described in Methods. Single basidiospore strain 5–6 also aggressively decayed birch and spruce (Text S1) and was selected for sequencing. Upper panels show scanning electron microscopy of radial (left) and transverse (right) sections of pine wood tracheids that were substantially eroded or completely degraded by P. gigantea strain 5–6 by week twelve. Transverse section of sound wood (bottom photo) provides comparison. (Bar  = 40 µm).
Figure 3
Figure 3. Comparative analysis of gene repertoires associated with degradation of plant cell wall polymers and extractives in 21 fungal genomes.
(A) Principal component analysis (PCA) of 21 fungi using 73 CAZy and 12 AA families (Dataset S1). GMC oxidoreductases methanol oxidase, glucose oxidase and aryl alcohol oxidase were excluded because confident functional assignments could not be made and/or their inclusion did not contribute to separation of white- and brown-rot species. (B) PCA of 21 fungi using genes encoding 14 enzymes involved in lipid metabolism (KEGG reference pathway 00071, Dataset S1). There is no significant segregation of white-rot and brown-rot fungi although P. gigantea was positioned in the third quadrant with B. adusta and P. carnosa. Symbols for white rot and brown rot fungi appear in blue and red, respectively. Tremella mesenterica is a mycoparasite. For raw data and contributions of the top 20 families see Dataset S1, Text S1 and Figures S2 and S3.
Figure 4
Figure 4. Number of genes identified in white rot fungi P. gigantea (Phlgi), P. chrysosporium (Phach), C. subvermispora (Cersu), and H. annosum (Hetan), and the brown rot fungus P. placenta (Pospl).
CROs were distinguished as previously described . Lytic polysaccharide monooxygenases were formerly classified as GH61 within the CAZy system (http://www.cazy.org/; [16]). Glycoside hydrolase family GH5 was subdivided as described (Figure S22).
Figure 5
Figure 5. P. gigantea transcriptome.
Scatterplots show the distribution of RNA-seq RPKM values (log2) for 11,376 P. gigantea genes when grown on basal salts containing A, acetone-extracted loblolly pine wood (ELP) or B, non-extracted loblolly pine wood (NELP) relative to glucose (Glc). Plot lines define 2-fold borders and best fit regression. Darkened points represent 164 (A) and 145 (B) transcripts accumulating>4-fold at p<0.01. Venn diagram (C) illustrates genes with RPKM signals>10 and upregulated>4-fold in NELP or ELP relative to Glc.
Figure 6
Figure 6. Number and expression of genes likely involved in lignocellulose degradation.
The number of genes encoding mass spectrometry-identified proteins was limited to those matching≥2 unique peptides after 5–9 days growth in media containing NELP or ELP. RPKM values>100 for RNA derived from these cultures were arbitrarily selected as the threshold for high transcript levels. Genes designated as ‘regulated’ showed significant accumulation (p<0.05;>2-fold) in NELP or ELP relative to glucose containing media. Methods and complete data are presented in Text S1 and Dataset S2.
Figure 7
Figure 7. P. gigantea transcriptome.
Scatterplot (A) shows the distribution of RNA-seq RPKM values (log2) for 11,376 P. gigantea genes when grown on basal salts containing acetone-extracted loblolly pine wood (ELP) or non-extracted loblolly pine wood (NELP). Lines define 2-fold borders and best fit regression. Darkened points represent 44 transcripts accumulating>4-fold at p<0.01. Venn diagram (B) illustrates genes with RPKM signals>10 and upregulated>4-fold in NELP relative to ELP. Twenty-two genes showed significant transcript accumulation in NELP relative to ELP suggesting potential response to resin and pitch content. Under these stringent thresholds (p<0.01;>4-fold), only one gene, a MCO model Phlgi1_129839, showed significant transcript accumulation in ELP relative to NELP. Additional detail appears in Tables 1-3. Detailed methods and complete data are presented in Text S1 and Dataset S2.
Figure 8
Figure 8. Glycoside hydrolase encoding genes show similar patterns of expression in media containing freshly ground and non-extracted loblolly pine wood (NELP) relative to the same substrate but extracted with acetone (ELP) to remove pitch and resins.
Proteins (upper panel) and transcripts (lower panel) were identified by LC-MS/MS and RNA-seq, respectively. Protein identification was limited to those with>2 unique peptides after five days incubation. Transcript upregulation was limited to significant accumulation (p<0.05;>2-fold) on NELP or ELP relative to glucose-containing medium. Secretome and transcriptome experimental details and complete data are presented in Text S1 and Dataset S2.
Figure 9
Figure 9. Glyoxalate shunt and proposed relationship to lipid oxidation when P. gigantea is cultivated on wood-containing media (ELP or NELP) relative to Glc medium.
Enzymes encoded by upregulated genes are black highlighted and associated with thickened arrows. Abbreviations: ABC-G1, ABC transporter associated with monoterpene tolerance; ADH/AO, Acyl-CoA dehydrogenase/oxidase; AH, Aconitate hydratase; CoA ligase, long fatty acid-CoA ligase; DLAT, Dihydrolipoyllysine-residue acetyltransferase; DLST, Dihydrolipoyllysine-residue succinyltransferase; EH, Enoyl-CoA hydratase; FDH, Formate dehydrogenase; FH, Fumarate hydratase; KT, Ketothiolase (acetyl-CoA C-acyltransferase); HAD, 3-Hydroxyacyl-CoA dehydrogenase; ICL, Isocitrate lyase; IDH, Isocitrate dehydrogenase; MDH, Malate dehydrogenase; MS, Malate synthase; ODH, Oxoglutarate dehydrogenase; OXA, Oxaloacetase; OXDC, Oxalate decarboxylase; OXO, Oxalate oxidase; PC, Pyruvate carboxylase; PDH, Pyruvate dehydrogenase; PEP, Phosphoenolpyruvate; PEPCK, Phosphoenolpyruvate carboxykinase; PEPK, Phosphoenolpyruvate kinase; SDH, succinate dehydrogenase. See Dataset S2 for detailed gene expression data.

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References

    1. Blanchette R (1991) Delignification by wood-decay fungi. Ann Rev Phytopath 29: 381–398.
    1. Eriksson K-EL, Blanchette RA, Ander P (1990) Microbial and enzymatic degradation of wood and wood components; Timell TE, editor. Berlin: Springer-Verlag.
    1. Rayner ADM, Boddy L (1988) Fungal decomposition of wood: its biology and ecology. Chichester: John Wiley and Sons.
    1. Kaarik AA (1974) Decomposition of wood. In: Dickinson CH, Pugh GJF, editors.Biology of plant litter composition.New York: Academic Press. pp.129–174.
    1. Shigo AL (1967) Succession of organisms in discoloration and decay wood. Int Rev For Res 2: 237–299.

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Grant support

The major portions of this work were performed under US Department of Agriculture Cooperative State, Research, Education, and Extension Service Grant 2007-35504-18257 (to DC and RAB). The US Department of Energy Joint Genome Institute is supported by the Office of Science of the US Department of Energy under Contract DE-AC02-05CH11231. This work was also supported by the HIPOP (BIO2011-26694) project of the Spanish Ministry of Economy and Competitiveness (MINECO) (to FJRD), the PEROXICATS (KBBE-2010-4-265397) and INDOX (KBBE-2013-.3.3-04-613549) European projects (to ATM), and the Chilean National Fund for Scientific and Technological Development Grant 1131030 (to LFL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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