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Summary The ectomycorrhizal (ECM) symbiosis has independently evolved from diverse types of saprotrophic ancestors. In this study, we seek to identify genomic signatures of the transition to the ECM habit within the hyper-diverse Russulaceae. We present comparative analyses of the genomic architecture and the total and secreted gene repertoires of 18 species across the order Russulales of which 13 are newly sequenced, including a representative of a saprotrophic member of Russulaceae, Gloeopeniophorella convolvens. The genomes of ECM Russulaceae are characterized by a loss of genes for plant cell-wall degrading enzymes (PCWDEs), an expansion of genome size through increased transposable element (TE) content, a reduction in secondary metabolism clusters, and an association of small secreted proteins (SSPs) with TE “nests”, or dense aggregations of TEs. Some PCWDEs have been retained or even expanded, mostly in a species-specific manner. The genome of Gloeopeniophorella convolvens possesses some characteristics of ECM genomes (e.g., loss of some PCWDEs, TE expansion, reduction in secondary metabolism clusters). Functional specialization in ectomycorrhizal decomposition may drive diversification. Accelerated gene evolution predates the evolution of the ECM habit, indicating that changes in genome architecture and gene content may be necessary to prime the evolutionary switch.

The family Russulaceae is considered an iconic lineage of mostly mushroom-forming basidiomycetes due to their importance as edible mushrooms in many parts of the world, and their ubiquity as ectomycorrhizal symbionts in both temperate and tropical forested biomes. Although much research has been focused on this group, a comprehensive or cohesive synthesis by which to understand the functional diversity of the group has yet to develop. Interest in ectomycorrhizal fungi, of which Russulaceae is a key lineage, is prodigious due to the important roles they play as plant root mutualists in ecosystem functioning, global carbon sequestration, and a potential role in technology development toward environmental sustainability. As one of the most species-diverse ectomycorrhizal lineages, the Russulaceae has recently been the focus of a dense sampling and genome sequencing initiative with the Joint Genome Institute aimed at untangling their functional roles and testing whether functional niche specialization exists for independent lineages of ectomycorrhizal fungi. Here we present a review of important studies on this group to contextualize what we know about its members' evolutionary history and ecosystem functions, as well as to generate hypotheses establishing the Russulaceae as a valuable experimental system.

The ectomycorrhizal (ECM) symbiosis has independently evolved from diverse types of saprotrophic ancestors. In this study, we seek to identify genomic signatures of the transition to the ECM habit within the hyperdiverse Russulaceae. We present comparative analyses of the genomic architecture and the total and secreted gene repertoires of 18 species across the order Russulales, of which 13 are newly sequenced, including a representative of a saprotrophic member of Russulaceae, Gloeopeniophorella convolvens. The genomes of ECM Russulaceae are characterized by a loss of genes for plant cell wall-degrading enzymes (PCWDEs), an expansion of genome size through increased transposable element (TE) content, a reduction in secondary metabolism clusters, and an association of small secreted proteins (SSPs) with TE ‘nests’, or dense aggregations of TEs. Here, some PCWDEs have been retained or even expanded, mostly in a species-specific manner. The genome of G. convolvens possesses some characteristics of ECM genomes (e.g. loss of some PCWDEs, TE expansion, reduction in secondary metabolism clusters). Functional specialization in ECM decomposition may drive diversification. Accelerated gene evolution predates the evolution of the ECM habit, indicating that changes in genome architecture and gene content may be necessary to prime the evolutionary switch.

Ectomycorrhizal fungi (EcM) are critical to the health and sustainability of many African ecosystems that include EcM-associated tree species. In Sub-Saharan Africa, three major EcM-dominated vegetation types can be distinguished: the Central African Guineo-Congolian rainforests, the West African Sudanian woodlands and the East African Zambezian Miombo woodlands. While the rainforests feature humid conditions with isolated patches of EcM trees amongst predominantly arbuscular mycorrhizal (AM) communities, the woodlands are characterised by drier soils and more vast continuous areas of EcM trees. We hypothesise that the isolation of EcM tree patches within the rainforest promotes a unique and potentially endemic EcM fungal community, while riparian forests found along rivers in woodland areas may serve as corridors, facilitating the spread of such rare taxa into woodland regions. In this study, we employ root tip metabarcoding combined with Species Hypothesis (SH) matching to characterise the EcM communities across these three vegetation types. Consistent with previous findings from fruit-body surveys and eDNA studies, our results show that Russulaceae is the most abundant EcM clade across all three regions. Other clades reveal greater discrepancy compared to their above-ground abundances, with notably high abundances of Inocybaceae , Thelephoraceae and Sebacinaceae , especially in woodlands. Conversely, Amanitaceae and Boletacaeae appear under-represented. Both Boletaceae and Elaphomycetaceae are found to be more prevalent in rainforest and riparian zones, illustrating the unique EcM community of the Guineo-Congolian rainforest. Our findings highlight the corridor potential of riparian areas in facilitating the spread of these rainforest endemics. This suggests that local edaphic and climatic conditions can override broad spatial patterns, such as distance decay, in community structure of African EcM. Moreover, we suggest a stronger effect of EcM host specificity than previously suggested for African fungal communities. Lastly, we assess the level of species-level representation and accuracy of taxonomic annotation of SHs within African Lactifluus . We confirm it to be one of the most thoroughly described and collected fungal genera on the continent, with over 80% of identified SHs represented in our herbarium collections.

The crown clade is one of two major groups in the subg. . An analysis of Chinese samples was performed based on the morphology, internal transcribed spacer (ITS) sequences, and multi-gene phylogenies of 28S nrLSU, 16S mtSSU, , , and . The results supported the independence of six new species: (sect. ), (subsect. ), (subsect. ), (subsect. ), , and (subsect. ) from Fagaceae forest habitats. Subsect. was newly proposed in sect. . Members of the new subsection include . , , and possibly . Our analyses also supported the claim that two species of (subsect. ) and (subsect. ) have a Eurasian distribution. The habitat and primary hosts of the main phylogenetic clades within related subsections were summarized and discussed.

Because orchids are dependent on mycorrhizal fungi for germination and establishment of seedlings, differences in the mycorrhizal communities associating with orchids can be expected to mediate the abundance, spatial distribution and coexistence of terrestrial orchids in natural communities. We assessed the small-scale spatial distribution of seven orchid species co-occurring in 25 × 25 m plots in two Mediterranean grasslands. In order to characterize the mycorrhizal community associating with each orchid species, 454 pyrosequencing was used. The extent of spatial clustering was assessed using techniques of spatial point pattern analysis. The community of mycorrhizal fungi consisted mainly of members of the Tulasnellaceae, Thelephoraceae and Ceratobasidiaceae, although sporadically members of the Sebacinaceae, Russulaceae and Cortinariaceae were observed. Pronounced differences in mycorrhizal communities were observed between species, whereas strong clustering and significant segregation characterized the spatial distribution of orchid species. However, spatial segregation was not significantly related to phylogenetic dissimilarity of fungal communities. Our results indicate that co-occurring orchid species have distinctive mycorrhizal communities and show strong spatial segregation, suggesting that mycorrhizal fungi are important factors driving niche partitioning in terrestrial orchids and may therefore contribute to orchid coexistence.

The ectomycorrhizal milkcap genus Lactifluus (Russulaceae) is commonly found in tropical and subtropical forests of Southeast Asia. During several sampling expeditions in Thailand, multiple collections of Lactifluus (Lf.) species with pleurotoid or small agaricoid basidiocarps were found. A molecular study was combined with a morphological study, in which the collections were compared with herbarium material. The molecular study indicated that four Thai collections belonged to undescribed species within Lactifluus section Gerardii, as was also the case for herbarium collections of a pleurotoid species from Nepal. One other collection from Thailand appeared closely related to Lf. uyedae, known only from Japan. Five species are described as new in the genus: Lf. auriculiformis, Lf. gerardiellus, Lf. bhandaryi, Lf. pulchrellus, and Lf. raspei.

Four new species of Russula subsection Sardoninae from northern and southwestern China under coniferous and deciduous trees are proposed as R. begonia, R. photinia, R. rhodochroa, and R. rufa. Illustrations and descriptions of R. gracillima, R. leucomarginata, R. roseola, and the above four new species are provided based on evidence of morphological characters and phylogenetic analyses of the internal transcribed spacer (ITS), as well as the multi-locus of mtSSU, nLSU, rpb1, rpb2 and tef1-α. The relationships between these new species and allied taxa are discussed.

Mycoheterotrophic plants (MHPs) rely on their mycorrhizal fungus for carbon and nutrient supply, thus a shift in mycobionts may play a crucial role in speciation. This study aims to explore the mycorrhizal diversity of two closely related and sympatric fully MHPs, Monotropastrum humile var. humile (Mhh) and M. humile var. glaberrimum (Mhg), and determine their mycorrhizal associations. A total of 1,108,710 and 1,119,071 ectomycorrhizal fungal reads were obtained from 31 Mhh and 31 Mhg, and these were finally assigned to 227 and 202 operational taxonomic units, respectively. Results show that sympatric Mhh and Mhg are predominantly associated with different fungal genera in Russulaceae. Mhh is consistently associated with members of Russula, whereas Mhg is associated with members of Lactarius. Associating with different mycobionts and limited sharing of fungal partners might reduce the competition and contribute to their coexistence. The ectomycorrhizal fungal communities are significantly different among the five forests in both Mhh and Mhg. The distinct mycorrhizal specificity between Mhh and Mhg suggests the possibility of different mycobionts triggered ecological speciation between sympatric species.

Forests on steep slopes constitute a significant proportion of European mountain areas and are important as production and protection forests. This study describes the soil fungal community structure in a European beech-dominated mountain forest stands in the Northern Calcareous Alps and investigates how it is determined by season and soil properties. Samples were collected at high spatial resolution in an area of ca. 100 m × 700 m in May (spring) and August (summer). Illumina MiSeq high-throughput sequencing of the ITS2-region revealed distinct patterns for the soil fungal communities. In contrast to other studies from temperate European beech forest stands, Ascomycota dominated the highly diverse fungal community, while ectomycorrhizal fungi were of lower abundance. Russulaceae, which are often among the dominant ectomycorrhizal fungi associated with European beech, were absent from all samples. Potentially plant pathogenic fungi were more prevalent than previously reported. Only subtle seasonal differences were found between fungal communities in spring and summer. Especially, dominant saprotrophic taxa were largely unaffected by season, while slightly stronger effects were observed for ectomycorrhizal fungi. Soil characteristics like pH and organic carbon content, on the other hand, strongly shaped abundant taxa among the saprotrophic fungal community.