The first steps of wood degradation by fungi lead to the release of toxic compounds known as extractives. To better understand how lignolytic fungi cope with the toxicity of these molecules, a transcriptomic analysis of Phanerochaete chrysosporium genes was performed in the presence of oak acetonic extracts. It reveals that in complement to the extracellular machinery of degradation, intracellular antioxidant and detoxification systems contribute to the lignolytic capabilities of fungi, presumably by preventing cellular damages and maintaining fungal health. Focusing on these systems, a glutathione transferase (P. chrysosporium GTT2.1 [PcGTT2.1]) has been selected for functional characterization. This enzyme, not characterized so far in basidiomycetes, has been classified first as a GTT2 compared to the Saccharomyces cerevisiae isoform. However, a deeper analysis shows that the GTT2.1 isoform has evolved functionally to reduce lipid peroxidation by recognizing high-molecular-weight peroxides as substrates. Moreover, the GTT2.1 gene has been lost in some non-wood-decay fungi. This example suggests that the intracellular detoxification system evolved concomitantly with the extracellular ligninolytic machinery in relation to the capacity of fungi to degrade wood.

White-rot fungi possess the unique ability to degrade and mineralize all the different components of wood. In other respects, wood durability, among other factors, is due to the presence of extractives that are potential antimicrobial molecules. To cope with these molecules, wood decay fungi have developed a complex detoxification network including glutathione transferases (GST). The interactions between GSTs from two white-rot fungi, Trametes versicolor and Phanerochaete chrysosporium, and an environmental library of wood extracts have been studied. The results demonstrate that the specificity of these interactions is closely related to the chemical composition of the extracts in accordance with the tree species and their localization inside the wood (sapwood vs heartwood vs knotwood). These data suggest that the fungal GSTome could reflect the chemical environment encountered by these fungi during wood degradation and could be a way to study their adaptation to their way of life.

is a wood-inhabiting agaricomycete known for its ability to cause strong white-rot decay on hardwood and for its high tolerance of phenolic compounds. The goal of the present work was to gain insights into the molecular biology and biochemistry of the heme-including class II and dye-decolorizing peroxidases secreted by this fungus. Proteomic analysis of the secretome of BRFM 1218 grown on oak wood revealed a set of 200 secreted proteins, among which were the dye-decolorizing peroxidaseDyP1 and the versatile peroxidase VP2. Both peroxidases were heterologously produced in, biochemically characterized, and tested for the ability to oxidize complex substrates. Both peroxidases were found to be active against several substrates under acidic conditions, and DyP1 was very stable over a relatively large pH range of 2.0 to 6.0, whileVP2 was more stable at pH 5.0 to 6.0 only. The thermostability of both enzymes was also tested, and DyP1 was globally found to be more stable thanVP2. After 180 min of incubation at temperatures ranging from 30 to 50°C, the activity of VP2 drastically decreased, with 10 to 30% of the initial activity retained. Under the same conditions,DyP1 retained 20 to 80% of its enzyme activity. The two proteins were catalytically characterized, and VP2 was shown to accept a wider range of reducing substrates thanDyP1. Furthermore, both enzymes were found to be active against two flavonoids, quercetin and catechin, found in oak wood, with VP2 displaying more rapid oxidation of the two compounds. They were tested for the ability to decolorize five industrial dyes, andVP2 presented a greater ability to oxidize and decolorize the dye substrates than DyP1. is a wood-inhabiting agaricomycete known for its ability to cause strong white-rot decay on hardwood and for its high tolerance of phenolic compounds. Among white-rot fungi, the basidiomycete has been extensively studied for its ability to degrade wood, specifically lignin, thanks to an extracellular oxidative enzymatic system. The corresponding oxidative system was previously studied in several works for classical lignin and manganese peroxidases, and in this study, two new components of the oxidative system of, one dye-decolorizing peroxidase and one versatile peroxidase, were biochemically characterized in depth and compared to other fungal peroxidases.

Glutathione transferases (GSTs) from the Xi and Omega classes have a catalytic cysteine residue, which gives them reductase activities. Until now, they have been assigned distinct substrates. While Xi GSTs specifically reduce glutathionyl-(hydro)quinones, Omega GSTs are specialized in the reduction of glutathionyl-acetophenones. Here, we present the biochemical and structural analysis of TvGSTX1 and TvGSTX3 isoforms from the wood-degrading fungus Trametes versicolor. TvGSTX1 reduces GS-menadione as expected, while TvGSTX3 reduces both Xi and Omega substrates. An in-depth structural analysis indicates a broader active site for TvGSTX3 due to specific differences in the nature of the residues situated in the C-terminal helix α9. This feature could explain the catalytic duality of TvGSTX3. Based on phylogenetic analysis, we propose that this duality might exist in saprophytic fungi and ascomycetes.

No abstract