The Paxillus involutus (Boletales, Paxillaceae) complex in Europe: Genetic diversity and morphological description of the new species Paxillus cuprinus, typification of P. involutus s.s., and synthesis of species boundaries

Pseudophylloporus Gen. nov. and Rubroleccinum Gen. nov., Two New Genera Revealed by Morphological and Phylogenetic Evidences in the Family Boletaceae from Subtropical China

Boletaceae, the largest and most diverse family of Boletales (Agaricomycetes and Basidiomycota), is both ecologically and economically important. Although many taxa have been described in China, the diversity of the family still remains incompletely understood. In the present study, Pseudophylloporus baishanzuensis gen. nov., sp. nov. and Rubroleccinum latisporus gen. nov., sp. nov. are proposed based on morphological and molecular phylogenetic analyses. These findings contribute to a deeper understanding of the diversity within the Boletaceae family.

X-ray fluorescence and XANES spectroscopy revealed diverse potassium chemistries and colocalization with phosphorus in the ectomycorrhizal fungus Paxillus ammoniavirescens

Ectomycorrhizal (ECM) fungi play a major role in forest ecosystems and managed tree plantations. Particularly, they facilitate mineral weathering and nutrient transfer towards colonized roots. Among nutrients provided by these fungi, potassium (K) has been understudied compared to phosphorus (P) or nitrogen (N). The ECM fungus Paxillus ammoniavirescens is a generalist species that interacts with the root of many trees and can directly transfer K to them, including loblolly pine. However, the forms of K that ECM fungi can store is still unknown. Here, we used synchrotron potassium X-ray fluorescence (XRF) and K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy on P. ammoniavirescens growing in axenic conditions to investigate the K chemistries accumulating in the center and the edge of the mycelium. We observed that various K forms accumulated in different part of the mycelium, including K-nitrate (KNO3), K-C-O compounds (such as K-tartrate K2(C4H4O6) and K-oxalate (K2C2O4)), K-S and K-P compounds. Saprotrophic fungi have been shown to excrete carboxylic acids, which in turn play a role in soil mineral weathering. Our finding of several K counter-ions to carboxylic acids may suggest that, besides their direct transfer to colonized roots, K ions can also be involved in the production of compounds necessary for sourcing nutrients from their surrounding environment by ECM fungi. Additionally, this work reveals that XANES spectroscopy can be used to identify the various forms of K accumulating in biological systems.

The ectomycorrhizal fungus Paxillus involutus positively modulates Castanea sativa Miller (var. Marsol) responses to heat and drought co-exposure

Castanea sativa Miller, a high-valuable crop for Mediterranean countries, is facing frequent and prolonged periods of heat and drought, severely affecting chestnut production. Aiming to tackle this problem, this study unraveled the influence of mycorrhizal association with the fungi Paxillus involutus (Batsch) on young chestnut plants' responses to combined heat (42 °C; 4 h/day) and drought (no irrigation until soil moisture reached 25%) over 21 days of stress exposure. Heat stress had no harmful effects on growth, photosynthesis, nor induced oxidative stress in either mycorrhizal (MR) or non-mycorrhizal (NMR) chestnut plants. However, drought (alone or combined) reduced the growth of NMR plants, affecting water content, leaf production, and foliar area, while also hampering net CO2 assimilation and carbon relations. The mycorrhizal association, however, mitigated the detrimental effects of both stresses, resulting in less susceptibility and fewer growth limitations in MR chestnut plants, which were capable of ensuring a proper carbon flow. Evaluation of the oxidative metabolism revealed increased lipid peroxidation and hydrogen peroxide levels in NMR plants under water scarcity, supporting their higher susceptibility to stress. Conversely, MR plants activated defense mechanisms by accumulating antioxidant metabolites (ascorbate, proline and glutathione), preventing oxidative damage, especially under the combined stress. Overall, drought was the most detrimental condition for chestnut growth, with heat exacerbating stress susceptibility. Moreover, mycorrhizal association with P. involutus substantially alleviated these effects by improving growth, water relations, photosynthesis, and activating defense mechanisms. Thus, this research highlights mycorrhization's potential to enhance C. sativa resilience against climate change, especially at early developmental stages.

Three new Melanogaster species (Boletales, Paxillaceae) from southwestern China based on morphological and molecular evidence

Three newly discovered Melanogaster species, namely M.cyaneus, M.diqingensis, and M.truncatisporus, are introduced and illustrated based on both morphological and molecular data from Sichuan and Yunnan provinces in China. A multigene phylogenetic analysis (nrITS, nrLSU, and rpb2) was performed mainly to verify the placement of the new species in Melanogaster. A second, nrITS-only phylogenetic analysis comprising more Melanogaster species for which only ITS sequences were available, was used to infer the relationship between the new species and as many known Melanogaster species as possible. Specimens of M.cyaneus, M.diqingensis, and M.truncatisporus formed three independent clades in a phylogenetic tree inferred from the ITS data set. The robust support from ITS for these clades and genetic similarity with other species being lower than 93.2% suggest that these three species are indeed distinct from the other Melanogaster species in the phylogeny. Morphologically, M.cyaneus is characterized by its blue or bluish gleba, light brown to yellowish brown peridium, and subglobose to globose basidiospores, 6.2-15 × 4.6-9.0 μm. Melanogasterdiqingensis is distinguished from other Melanogaster species by its pale yellow to brown-yellow peridium and obovate to subglobose basidiospores, 3.0-5.1 × 2.0-4.0 μm. Melanogastertruncatisporus is diagnosed by its subglobose to globose or irregularly elongate-pyriform basidiomata, pale yellow to deeply orange-yellow peridium, and subglobose to globose or pyriform, truncate basidiospores. Additionally, infrageneric classification based on the number of peridium layers, the average thickness of the peridium, and the average length and width of basidiospores was tested with M.cyaneus, M.diqingensis, and M.truncatisporus. Orthogonal partial least squares discriminant (OPLS-DA) analysis placed the three new species within the Melanogaster, Rivulares, and Variegati sections, respectively. However, the morphologically circumscribed sections were not monophyletic in the phylogenetic tree. Therefore, the current infrageneric classification should be abandoned.

A guide to mycetisms: A toxicological and preventive overview

Fungi are often considered a delicacy and are primarily cultivated and harvested, although numerous species are responsible for intoxication due to toxin content. Foodborne diseases are a significant public health concern, causing approximately 420 000 deaths and 600 million morbidities yearly, of which mushroom poisoning is one of the leading causes. Epidemiological data on non-cultivated mushroom poisoning in individual countries are often unrepresentative, as intoxication rarely requires emergency intervention. On the other hand, the lack of specialist knowledge among medical personnel about the toxicological manifestations of mushroom consumption may result in ineffective therapeutic interventions. This work aims to provide an easy-to-consult and wide-ranging tool useful for better understanding the variability of mushroom intoxications, the associated symptoms, and the main treatments for the most severe cases, given the absence of a complete species mapping tool toxic. Moreover, we establish an effective collection network that describes the incidence of mushroom poisonings by reporting the species and associated toxicological manifestations for each case. In conclusion, we highlight the need to establish appropriate primary prevention interventions, such as training the affected population and increasing consultancy relationships between mycological experts and specialised healthcare personnel.

The ectomycorrhizal fungus Paxillus ammoniavirescens influences the effects of salinity on loblolly pine in response to potassium availability

Salinity is an increasing problem in coastal areas affected by saltwater intrusion, with deleterious effects on tree health and forest growth. Ectomycorrhizal (ECM) fungi may improve the salinity tolerance of host trees, but the impact of external potassium (K+ ) availability on these effects is still unclear. Here, we performed several experiments with the ECM fungus Paxillus ammoniavirescens and loblolly pine (Pinus taeda L.) in axenic and symbiotic conditions at limited or sufficient K+ and increasing sodium (Na+ ) concentrations. Growth rate, biomass, nutrient content, and K+ transporter expression levels were recorded for the fungus, and the colonization rate, root development parameters, biomass, and shoot nutrient accumulation were determined for mycorrhizal and non-mycorrhizal plants. P. ammoniavirescens was tolerant to high salinity, although growth and nutrient concentrations varied with K+ availability and increasing Na+ exposure. While loblolly pine root growth and development decreased with increasing salinity, ECM colonization was unaffected by pine response to salinity. The mycorrhizal influence on loblolly pine salinity response was strongly dependent on external K+ availability. This study reveals that P. ammoniavirescens can reduce Na+ accumulation of salt-exposed loblolly pine, but this effect depends on external K+ availability.

First report of Cladobotryumverticillatum (Ascomycota, Hypocreaceae) causing cobweb disease on Paxillusinvolutus

Paxillus, a type of ectomycorrhizal fungi distributed widely in the world, is also an essential category for researching bioactive substances and pharmacological functions. We discovered fruitbodies of Paxillusinvolutus covered in a layer of white mycelium in 2020. Cladobotryumverticillatum, a pathogenic fungus related to cobweb disease, was isolated and identified based on morphological and phylogenetic features. Koch's postulates were used to confirm the pathogenicity. The host range test revealed that C.verticillatum could cause disease in all examined mushrooms except Ganodermasichuanense. To our knowledge, C.verticillatum is a new record species in China and a new pathogen on Paxillusinvolutus.

Lipo-chitooligosaccharides as regulatory signals of fungal growth and development

Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Here, we show that many other fungi also produce LCOs. We tested 59 species representing most fungal phyla, and found that 53 species produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment affects spore germination, branching of hyphae, pseudohyphal growth, and transcription in non-symbiotic fungi from the Ascomycete and Basidiomycete phyla. Our findings suggest that LCO production is common among fungi, and LCOs may function as signals regulating fungal growth and development.

Comparative mitogenome analysis of two ectomycorrhizal fungi (Paxillus) reveals gene rearrangement, intron dynamics, and phylogeny of basidiomycetes

In this study, the mitogenomes of two Paxillus species were assembled, annotated and compared. The two mitogenomes of Paxillus involutus and P. rubicundulus comprised circular DNA molecules, with the size of 39,109 bp and 41,061 bp, respectively. Evolutionary analysis revealed that the nad4L gene had undergone strong positive selection in the two Paxillus species. In addition, 10.64 and 36.50% of the repetitive sequences were detected in the mitogenomes of P. involutus and P. rubicundulus, respectively, which might transfer between mitochondrial and nuclear genomes. Large-scale gene rearrangements and frequent intron gain/loss events were detected in 61 basidiomycete species, which revealed large variations in mitochondrial organization and size in Basidiomycota. In addition, the insertion sites of the basidiomycete introns were found to have a base preference. Phylogenetic analysis of the combined mitochondrial gene set gave identical and well-supported tree topologies, indicating that mitochondrial genes were reliable molecular markers for analyzing the phylogenetic relationships of Basidiomycota. This study is the first report on the mitogenomes of Paxillus, which will promote a better understanding of their contrasted ecological strategies, molecular evolution and phylogeny of these important ectomycorrhizal fungi and related basidiomycete species.

Psiloboletinus is an independent genus sister to Suillus

The genus Psiloboletinus was proposed by Rolf Singer in 1945 based on Phylloporus lariceti, a species that associates with Larix in the Altai Mountains of central and eastern Asia. However, this classification has been controversial due to the morphological similarity to known genera Boletinus and Fuscoboletinus. Because of the lack of fresh material to study, the phylogenetic position of Psiloboletinus has remained unknown since its publication. However, the recently described species Suillus foetidus reported from northeast China allows this issue to be reexamined and resolved. Through morphological observations and comparison, we find that S. foetidus is a heterotypic synonym of Ps. lariceti. Furthermore, Psiloboletinus should be retained as an independent genus sister to Suillus based on molecular phylogenetic evidence and morphological features.

Notes, outline and divergence times of Basidiomycota

The Basidiomycota constitutes a major phylum of the kingdom Fungi and is second in species numbers to the Ascomycota. The present work provides an overview of all validly published, currently used basidiomycete genera to date in a single document. An outline of all genera of Basidiomycota is provided, which includes 1928 currently used genera names, with 1263 synonyms, which are distributed in 241 families, 68 orders, 18 classes and four subphyla. We provide brief notes for each accepted genus including information on classification, number of accepted species, type species, life mode, habitat, distribution, and sequence information. Furthermore, three phylogenetic analyses with combined LSU, SSU, 5.8s, rpb1, rpb2, and ef1 datasets for the subphyla Agaricomycotina, Pucciniomycotina and Ustilaginomycotina are conducted, respectively. Divergence time estimates are provided to the family level with 632 species from 62 orders, 168 families and 605 genera. Our study indicates that the divergence times of the subphyla in Basidiomycota are 406–430 Mya, classes are 211–383 Mya, and orders are 99–323 Mya, which are largely consistent with previous studies. In this study, all phylogenetically supported families were dated, with the families of Agaricomycotina diverging from 27–178 Mya, Pucciniomycotina from 85–222 Mya, and Ustilaginomycotina from 79–177 Mya. Divergence times as additional criterion in ranking provide additional evidence to resolve taxonomic problems in the Basidiomycota taxonomic system, and also provide a better understanding of their phylogeny and evolution.

Extreme levels of mycophilia documented in Mazovia, a region of Poland

BACKGROUND

The paper presents documentation of the traditional use of wild edible mushrooms in Mazovia (33,900 km²), a region of Poland.

METHODS

A total of 695 semi-structured interviews were carried out among local informants in 38 localities proportionally distributed throughout the study area (one locality approximately every 30 km), asking which mushrooms they collected and how. The species utilized were identified using visual props, morphological identification of voucher specimens, and DNA barcoding.

RESULTS

Altogether, 92 taxa identified to the species or genus level were recorded, among them 76 species used as food, 21 taxa known as toxic, and 11 taxa used for non-culinary purposes. Out of 76 identified edible fungi species, 47% (36 species) were identified using ITS DNA barcode method. Eleven of them were identified exclusively by molecular analysis. The mean number of edible taxa mentioned per interview was 9.5. Two species new to the mycobiota of Poland, Hydnum ellipsosporum and Paxillus cuprinus, were found. Frequent interaction with mushroom collectors enabled the transcription of local folk taxonomy into proper taxonomic classification and the definition of changes in local preferences concerning wild fungi collection.

CONCLUSIONS

The list of species utilized is the longest regional list of edible mushrooms ever recorded during ethnomycological field research, putting the inhabitants of the studied region at the top of the mycophilia spectrum.

Soil propagule banks of ectomycorrhizal fungi share many common species along an elevation gradient

We conducted bioassay experiments to investigate the soil propagule banks of ectomycorrhizal (EM) fungi in old-growth forests along an elevation gradient and compared the elevation pattern with the composition of EM fungi on existing roots in the field. In total, 150 soil cores were collected from three forests on Mt. Ishizuchi, western Japan, and subjected to bioassays using Pinus densiflora and Betula maximowicziana. Using molecular analyses, we recorded 23 EM fungal species in the assayed propagule banks. Eight species (34.8 %) were shared across the three sites, which ranged from a warm-temperate evergreen mixed forest to a subalpine conifer forest. The elevation pattern of the assayed propagule banks differed dramatically from that of EM fungi on existing roots along the same gradient, where only a small proportion of EM fungal species (3.5 %) were shared across sites. The EM fungal species found in the assayed propagule banks included many pioneer fungal species and composition differed significantly from that on existing roots. Furthermore, only 4 of 23 species were shared between the two host species, indicating a strong effect of bioassay host identity in determining the propagule banks of EM fungi. These results imply that the assayed propagule bank is less affected by climate compared to EM fungal communities on existing roots. The dominance of disturbance-dependent fungal species in the assayed propagule banks may result in higher ecosystem resilience to disturbance even in old-growth temperate forests.