| 1. |
- Braesel, Jana, et al.
(author)
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Three Redundant Synthetases Secure Redox-Active Pigment Production in the Basidiomycete Paxillus involutus.
- 2015
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In: Chemistry and Biology. - : Elsevier BV. - 1879-1301 .- 1074-5521. ; 22:10, s. 1325-1334
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Journal article (peer-reviewed)abstract
- The symbiotic fungus Paxillus involutus serves a critical role in maintaining forest ecosystems, which are carbon sinks of global importance. P. involutus produces involutin and other 2,5-diarylcyclopentenone pigments that presumably assist in the oxidative degradation of lignocellulose via Fenton chemistry. Their precise biosynthetic pathways, however, remain obscure. Using a combination of biochemical, genetic, and transcriptomic analyses, in addition to stable-isotope labeling with synthetic precursors, we show that atromentin is the key intermediate. Atromentin is made by tridomain synthetases of high similarity: InvA1, InvA2, and InvA5. An inactive atromentin synthetase, InvA3, gained activity after a domain swap that replaced its native thioesterase domain with that of InvA5. The found degree of multiplex biosynthetic capacity is unprecedented with fungi, and highlights the great importance of the metabolite for the producer.
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| 2. |
- Karlsson, Magnus, et al.
(author)
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Insights on the Evolution of Mycoparasitism from the Genome of Clonostachys rosea
- 2015
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In: Genome Biology and Evolution. - : Oxford University Press (OUP). - 1759-6653. ; 7:2, s. 465-480
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Journal article (peer-reviewed)abstract
- Clonostachys rosea is a mycoparasitic fungus that can control several important plant diseases. Here, we report on the genome sequencing of C. rosea and a comparative genome analysis, in order to resolve the phylogenetic placement of C. rosea and to study the evolution of mycoparasitism as a fungal lifestyle. The genome of C. rosea is estimated to 58.3 Mb, and contains 14,268 predicted genes. A phylogenomic analysis shows that C. Tosco clusters as sister taxon to plant pathogenic Fusarium species, with mycoparasitic/saprotrophic Tfichoderma species in an ancestral position. A comparative analysis of gene family evolution reveals several distinct differences between the included mycoparasites. Clonostachys rosea contains significantly more ATP-binding cassette (ABC) transporters, polyketide synthases, cytochrome P450 monooxygenases, pectin lyases, glucose-methanol-choline oxidoreductases, and lytic polysaccharide monooxygenases compared with other fungi in the Hypocreales. Interestingly, the increase of ABC transporter gene number in C. rosea is associated with phylogenetic subgroups B (multidrug resistance proteins) and G (pleiotropic drug resistance transporters), whereas an increase in subgroup C (multidrug resistance-associated proteins) is evident in Tfichoderma virens. In contrast with mycoparasitic Tfichoderma species, C. rosea contains very few chitinases. Expression of six group B and group G ABC transporter genes was induced in C. rosea during exposure to the Fusafium mycotoxin zearalenone, the fungicide Boscalid or metabolites from the biocontrol bacterium Pseudomonas chiororaphis. The data suggest that tolerance toward secondary metabolites is a prominent feature in the biology of C. rosea.
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| 3. |
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| 4. |
- Shah, Firoz, et al.
(author)
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Involutin is a Fe3+ reductant Secreted by the Ectomycorrhizal Fungus Paxillus involutus during Fenton-based Decomposition of Organic Matter.
- 2015
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In: Applied and Environmental Microbiology. - 0099-2240. ; 81:24, s. 8427-8433
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Journal article (peer-reviewed)abstract
- Ectomycorrhizal fungi play a key role in mobilizing nutrients embedded in recalcitrant organic matter complexes, thereby increasing nutrient accessibility to the host plant. Recent study have shown that during assimilation of nutrients, the ectomycorrhizal fungus Paxillus involutus decomposes organic matter using an oxidative mechanism involving Fenton chemistry (Fe(2+) + H2O2 + H(+) → Fe(3+) + •OH + H2O) similar to that of brown-rot wood-decaying fungi. In such fungi, secreted metabolites are one of the components that drive one-electron reductions of Fe(3+) and O2, generating Fenton chemistry reagents. Here, we investigated whether such a mechanism is also implemented by P. involutus during organic matter decomposition. Activity-guided purification was performed to isolate the Fe(3+)-reducing principle secreted by P. involutus during growth on maize compost extract. The Fe(3+)-reducing activity correlated with the presence of one compound. Mass spectrometry and NMR identified this compound as the diarylcyclopentenone involutin. A major part of the involutin produced by P. involutus during organic matter decomposition was secreted into the medium and the metabolite was not detected when the fungus was grown on a mineral nutrient medium. We also demonstrated that in the presence of H2O2, involutin has the capacity to drive an in vitro Fenton reaction via Fe(3+) reduction. Our results show that the mechanism for reducing Fe(3+) and generating hydroxyl radicals via Fenton chemistry by ectomycorrhizal fungi during organic matter decomposition is similar to that expressed by the evolutionarily related brown-rot saprotrophs during wood decay.
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| 5. |
- Shah, Firoz, et al.
(author)
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Secretion of iron(III)-reducing metabolites during protein acquisition by the ectomycorrhizal fungus paxillus involutus
- 2021
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In: Microorganisms. - : MDPI AG. - 2076-2607. ; 9:1
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Journal article (peer-reviewed)abstract
- The ectomycorrhizal fungus Paxillus involutus decomposes proteins using a two-step mechanism, including oxidation and proteolysis. Oxidation involves the action of extracellular hydroxyl radicals (•OH) generated by the Fenton reaction. This reaction requires the presence of iron(II). Here, we monitored the speciation of extracellular iron and the secretion of iron(III)-reducing metabolites during the decomposition of proteins by P. involutus. X-ray absorption spectroscopy showed that extracellular iron was mainly present as solid iron(III) phosphates and oxides. Within 1 to 2 days, these compounds were reductively dissolved, and iron(II) complexes were formed, which remained in the medium throughout the incubation. HPLC and mass spectrometry detected five extracellular iron(III)-reducing metabolites. Four of them were also secreted when the fungus grew on a medium containing ammonium as the sole nitrogen source. NMR identified the unique iron(III)-reductant as the diarylcyclopentenone involutin. Involutin was produced from day 2, just before the elevated •OH production, preceding the oxidation of BSA. The other, not yet fully characterized iron(III)-reductants likely participate in the rapid reduction and dissolution of solid iron(III) complexes observed on day one. The production of these metabolites is induced by other environmental cues than for involutin, suggesting that they play a role beyond the Fenton chemistry associated with protein oxidation.
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