Search

The brown rot fungus Fomitopsis pinicola efficiently depolymerizes wood cellulose via the combined activities of oxidative and hydrolytic enzymes. Mass spectrometric analyses of culture filtrates identified specific proteins, many of which were differentially regulated in response to substrate composition.

Wood-decaying fungi tend to have characteristic substrate ranges that partly define their ecological niche. Fomitopsis pinicola is a brown rot species of Polyporales that is reported on 82 species of softwoods and 42 species of hardwoods. We analyzed gene expression levels of F. pinicola from submerged cultures with ground wood powder (sampled at 5 days) or solid wood wafers (sampled at 10 and 30 days), using aspen, pine, and spruce substrates (aspen was used only in submerged cultures). Fomitopsis pinicola expressed similar sets of wood-degrading enzymes typical of brown rot fungi across all culture conditions and time points. Nevertheless, differential gene expression was observed across all pairwise comparisons of substrates and time points. Genes exhibiting differential expression encode diverse enzymes with known or potential function in brown rot decay, including laccase, benzoquinone reductase, aryl alcohol oxidase, cytochrome P450s, and various glycoside hydrolases. Comparing transcriptomes from submerged cultures and wood wafers, we found that culture conditions had a greater impact on global expression profiles than substrate wood species. These findings highlight the need for standardization of culture conditions in studies of gene expression in wood-decaying fungi.IMPORTANCE All species of wood-decaying fungi occur on a characteristic range of substrates (host plants), which may be broad or narrow. Understanding the mechanisms that allow fungi to grow on particular substrates is important for both fungal ecology and applied uses of different feedstocks in industrial processes. We grew the wood-decaying polypore Fomitopsis pinicola on three different wood species—aspen, pine, and spruce—under various culture conditions. We found that F. pinicola is able to modify gene expression (transcription levels) across different substrate species and culture conditions. Many of the genes involved encode enzymes with known or predicted functions in wood decay. This study provides clues to how wood-decaying fungi may adjust their arsenal of decay enzymes to accommodate different host substrates.

Efficient lignin depolymerization is unique to the wood decay basidiomycetes, collectively referred to as white rot fungi. Phanerochaete chrysosporium simultaneously degrades lignin and cellulose, whereas the closely related species, Ceriporiopsis subvermispora, also depolymerizes lignin but may do so with relatively little cellulose degradation. To investigate the basis for selective ligninolysis, we conducted comparative genome analysis of C. subvermispora and P. chrysosporium. Genes encoding manganese peroxidase numbered 13 and five in C. subvermispora and P. chrysosporium, respectively. In addition, the C. subvermispora genome contains at least seven genes predicted to encode laccases, whereas the P. chrysosporium genome contains none. We also observed expansion of the number of C. subvermispora desaturase-encoding genes putatively involved in lipid metabolism. Microarray-based transcriptome analysis showed substantial up-regulation of several desaturase and MnP genes in wood-containing medium. MS identified MnP proteins in C. subvermispora culture filtrates, but none in P. chrysosporium cultures. These results support the importance of MnP and a lignin degradation mechanism whereby cleavage of the dominant nonphenolic structures is mediated by lipid peroxidation products. Two C. subvermispora genes were predicted to encode peroxidases structurally similar to P. chrysosporium lignin peroxidase and, following heterologous expression in Escherichia coli, the enzymes were shown to oxidize high redox potential substrates, but not Mn2. Apart from oxidative lignin degradation, we also examined cellulolytic and hemicellulolytic systems in both fungi. In summary, the C. subvermispora genetic inventory and expression patterns exhibit increased oxidoreductase potential and diminished cellulolytic capability relative to P. chrysosporium.

An investigation carried out to evaluate wood decay present at the three historic huts in the Ross Sea region, identify fungi isolated from the decayed wood by using internal transcribed spacer (ITS) sequences of ribosomal DNA (rDNA), to determine where these fungi are located in the historic huts, and evaluate their decay potential in laboratory studies, is presented. The results of the study may provide information crucial to conservators for preservation of these historic sites as well as new information on decay fungi and elucidate the type and extent of degradation that has occurred.

The emerald ash borer (EAB, Agrilus planipennis) is a devastating invasive pest that has killed millions of ash trees in the United States and Canada. EAB was discovered in the US in 2002 and first reported in Minnesota in 2009. It attacks ash trees that are native to the United States, including Fraxinus americana (white ash), F. nigra (black ash) and F. pennsylvanica (green ash). It also attacks Chionanthus virginicus (white fringe tree). Seven species of fungi isolated and identified only from EAB-infested trees in a previous study as having the potential to cause cankers were used to test their pathogenicity in F. americana (white ash). The fungi used were Cytospora pruinosa, Diplodia mutila, Diplodia seriata, Paraconiothyrium brasiliense, Phaeoacremonium minimum, Phaeoacremonium scolyti, and Thyronectria aurigera. Two field experiments that used F. americana used two inoculation methods: woodchip and agar plug inoculations. Results indicated that all of the fungi tested caused cankers in varying amounts, as compared to the controls. The largest cankers were caused by D. mutila (270 mm2), C. pruinosa (169 mm2), and D. seriata (69 mm2). All fungi except for T. aurigera were re-isolated and sequenced to confirm Kochs' postulates. Canker-causing fungi found in association with EAB galleries have the potential to contribute to tree dieback and mortality. [ABSTRACT FROM AUTHOR]