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Department of Natural History, Royal Ontario Museum, and Department of Botany, University of Toronto, Toronto, Ontario, M5S 2C6 Canada
R. Henrik Nilsson
Göteborg University, Department of Plant and Environmental Sciences, Box 461, 405 30 Göteborg, Sweden
Brenda Koster
Department of Botany, University of Toronto, Toronto, Ontario, M5S 3B2 Canada
Susie M. Dunham
Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, Oregon 97331
Torsten Bernauer
Universität Kassel, FB 18 Naturwissenschaften, FG Ökologie, Heinrich-Plett-Straße 40, DE-34132, Kassel, Germany
P. Brandon Matheny
Biology Department, Clark University, 950 Main Street, Worcester, Massachusetts 01610
Teresita M. Porter
Department of Botany, University of Toronto, Toronto, Ontario, M5S 3B2 Canada
Simona Margaritescu
Royal Ontario Museum, Toronto, Ontario, M5S 2C6, Canada
Michael Weiß
Sigisfredo Garnica
Spezielle Botanik und Mykologie, Universität Tübingen, Auf der Morgenstelle 1, D-72076, Tübingen, Germany
Eric Danell
Museum of Evolution, Botany Section, Uppsala University, Norbyv. 16, SE-75236, Uppsala, Sweden
Gitta Langer
Ewald Langer
Universität Kassel, FB 18 Naturwissenschaften, FG Ökologie, Heinrich-Plett-Straße 40, DE-34132, Kassel, Germany
Ellen Larsson
Karl-Henrik Larsson
Göteborg University, Department of Plant and Environmental Sciences, Box 461, SE-40530, Göteborg, Sweden
Rytas Vilgalys
Department of Biology, Box 90338, Duke University, Durham, North Carolina 27708
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIAL AND METHODSRESULTS AND DISCUSSIONCONCLUSIONLITERATURE CITED |
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We reassessed the circumscription of the cantharelloid clade and identified monophyletic groups by using nLSU, nSSU, mtSSU and RPB2 sequence data. Results agreed with earlier studies that placed the genera Cantharellus, Craterellus, Hydnum, Clavulina, Membranomyces, Multiclavula, Sistotrema, Botryobasidium and the family Ceratobasidiaceae in that clade. Phylogenetic analyses support monophyly of all genera except Sistotrema, which was highly polyphyletic. Strongly supported monophyletic groups were: (i) Cantharellus-Craterellus, Hydnum, and the Sistotrema confluens group; (ii) Clavulina-Membranomyces and the S. brinkmannii-oblongisporum group, with Multiclavula being possibly sister of that clade; (iii) the Sistotrema eximum-octosporum group; (iv) Sistotrema adnatum and S. coronilla. Positions of Sistotrema raduloides and S. athelioides were unresolved, as were basal relationships. Botryobasidium was well supported as the sister taxon of all the above taxa, while Ceratobasidiaceae was the most basal lineage. The relationship between Tulasnella and members of the cantharelloid clade will require further scrutiny, although there is cumulative evidence that they are probably sister groups. The rates of molecular evolution of both the large and small nuclear ribosomal RNA genes (nuc-rDNA) are much higher in Cantharellus, Craterellus and Tulasnella than in the other cantharelloid taxa, and analyses of nuc-rDNA sequences strongly placed Tulasnella close to Cantharellus-Craterellus. In contrast analyses with RPB2 and mtSSU sequences placed Tulasnella at the base of the cantharelloid clade. Our attempt to reconstruct a "supertree" from tree topologies resulting from separate analyses that avoided phylogenetic reconstruction problems associated with missing data and/or unalignable sequences proved unsuccessful.
Key words: Basidiomycota, Fungi, mtSSU, nLSU, nSSU, phylogeny, RPB2
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTS AND DISCUSSIONCONCLUSIONLITERATURE CITED |
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to accommodate a morphologically diverse group of fungi that consistently clustered with the chanterelles (Cantharellus L.: Fr.) in molecular phylogenetic analyses. As presently recognized the cantharelloid clade comprises about 300 known species, making it a much smaller clade than most of the other major basidiomycete lineages (Hibbett and Thorn 2001, Binder et al 2005). Cantharellus was set apart from the other gilled fungi early in the history of mycology (Fries 1821) on the basis that its members form "false" gills resulting from a plicate hymenophore rather than developing "true" gills like most other mushrooms. Craterellus was created by Persoon (1825) to distinguish from Cantharellus those chanterelles having a hollow stipe, but the distinction between these two genera has long been controversial (Corner 1966, Petersen 1971). Gomphus Pers.: Fr. is another genus with a similarly plicate hymenial surface that traditionally was classified in the vicinity of Cantharellus in the order Cantharellales. Hydnum L.: Fr. is a genus with striking morphological, ecological and culinary similarities to the chanterelles except for having a spinose rather than a lamellate hymenophore, and most authors also classified it in the Cantharellales. Over the years the circumscription and the composition of the order Cantharellales has been much in flux. While sometimes restricted to the taxa mentioned above, the Cantharellales was also a place-holder for a multitude of aphyllophoroid genera as diverse as the toothed fungi Auriscalpium and Sarcodon, the clavarioid and coralloid genera Clavaria, Clavariadelphus, Clavulina, Clavulinopsis, Multiclavula, Typhula, Pterula and Ramaria, the cauliflower genus Sparassis, and poroid Albatrellus (Donk 1964).
Hibbett et al (1997) were the first to use DNA sequencing and phylogenetic principles for inferring evolutionary relationships from a broad taxonomic sampling of homobasidiomycetes. These authors used sequence data from both the nuclear (nSSU) and mitochondrial (mtSSU) small ribosomal subunit RNA genes that indicated a common origin of Cantharellus, Hydnum, Clavulina, Multiclavula and members of the corticioid genus Botryobasidium, while placing Gomphus, Clavaria and several other putative members of the Cantharellales in separate clades. Subsequent molecular phylogenetic studies indicated that the resupinate taxa Sistotrema, Membranomyces and the Ceratobasidiaceae were also members of the cantharelloid clade (Pine et al 1999, Hibbett et al 2000, Hibbett and Donoghue 2001, Hibbett and Binder 2002, Binder and Hibbett 2002, Larsson et al 2004, Binder et al 2005).
Hibbett and Thorn (2001) proposed the inclusion of the traditional heterobasidiomycete genus Tulasnella in the cantharelloid clade based on a mtLSU phylogeny in Bruns et al (1998) and unpublished mtSSU data. In the most recent and most comprehensive phylogenetic study of the homobasidiomycetes, Binder et al (2005) used a four-gene dataset comprising nSSU, mtSSU, nLSU and mtLSU sequences that placed Tulasnella as a sister group of all the other cantharelloid taxa. That study also indicated that the Sebacinales could be included in the cantharelloid clade.
All studies to date that included members of the cantharelloid clade were either within a much broader basidiomycete framework (as referred above) or restricted to genus-level investigations (Dahlman et al 2000, Dunham et al 2003, Thacker and Henkel 2004, Henkel et al 2005). Studies relying on nSSU and/or nLSU sequences of Cantharellus, Craterellus and/or Tulasnella for inference of intergeneric phylogenetic relationships have been plagued with alignment difficulties due to an accelerated rate of molecular evolution of the nuclear rDNA genes in these taxa, resulting in their placement on distinctively long branches. Moreover most earlier studies used parsimony or distance-based reconstruction methods that are known to be more sensitive to the long-branch attraction problem than likelihood-based methods and therefore can result in misleading inference of evolutionary relationships (Felsenstein 1978, Huelsenbeck 1997, Cunningham et al 1998, Poe and Swofford 1999). A reassessment of the cantharelloid clade in a more focused taxonomic context therefore is warranted.
The aim of the present study was to bring together data from previous molecular phylogenetic studies and combine them with newly produced sequences to: (i) reassess the circumscription of the cantharelloid clade; (ii) identify monophyletic groups within that clade; and (iii) determine whether the accelerated rate of molecular evolution in the rDNA of Cantharellus, Craterellus and Tulasnella also occurs in RPB2 and how rate variation affects inference of phylogenetic relationships in the clade. We hypothesized that the long-branch problem associated with the placement of Cantharellus, Craterellus and Tulasnella in earlier published rDNA phylogenies can be solved with the use of strict sequence alignments.
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MATERIAL AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTS AND DISCUSSIONCONCLUSIONLITERATURE CITED |
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) and empirically as described in Hofstetter et al (2002) and Miadlikowska and Lutzoni (2004). (See SUPPLEMENTARY INFORMATION.)
Three problems restrained us in constructing a "super-matrix" for a phylogenetic reassessment of the cantharelloid clade. First, many isolates had missing data at one or more loci. Second, we encountered several difficulties in the alignment of both nLSU and nSSU sequences from members of Cantharellus, Craterellus and Tulasnella with those from members of the other genera. Third, we found significant incongruence in the phylogenetic placement of Tulasnella depending on the gene analyzed (see SUPPLEMENTARY FIG. 1 and below). We attempted to reconstruct a "supertree" to bring together the separate (but optimized) analyses into a single phylogenetic tree, as described in Sanderson et al (1998). Only strongly supported nodes (0.95 pp or greater) were scored to create the matrix representation submitted to maximum parsimony analysis for a supertree reconstruction.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTS AND DISCUSSIONCONCLUSIONLITERATURE CITED |
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, Binder et al 2005) and to identify monophyletic lineages within that clade. We produced many novel nLSU, nSSU, mtSSU and RPB2 sequences and combined them with data available in the NCBI and AFTOL public databases to conduct multiple phylogenetic analyses from both separate and concatenated datasets. (Results are presented in supplement.) They were generally consistent with earlier findings that used more limited taxa and character samplings and provided many novel insights about phylogenetic relationships within the clade.
Novel findings include the resolution of a core cantharelloid clade composed of at least three distinct lineages (FIG. 1): (i) Cantharellus, Craterellus, Hydnum and the S. confluensmuscicola group; (ii) Clavulina, Membranomyces and the S. brinkmannii-oblongisporum group; and (iii) the S. eximum-octosporum group. Multiclavula and other Sistotrema species also belong to that clade but their position was not fully resolved. We also demonstrate that Sistotrema is highly polyphyletic, that Botryobasidium is the sister group of the core cantharelloid clade and that Sebacinales do not belong to this clade. The latter finding solves the conflicting placement of this order between the studies of Weiß et al (2004a, b) and Binder et al (2005).
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The removal of so many characters, which otherwise aligned well within subgroups, resulted in a significant loss of phylogenetic resolution within terminal clades. To elude this problem and also to avoid pitfalls associated with "supermatrices" containing many missing data (see Wiens 1998, 2003) we conducted multiple separate analyses and examined the possibility of using a "supertree" method (Sanderson et al 1998) to eventually combine these disparate datasets. Our attempt to reconstruct a meaningful supertree from the topologies (FIG. 1
and SUPPLEMENTARY FIG. 1) was largely unsuccessful (data not shown). This could be explained by the findings from a simulation study by Bininda-Emonds and Sanderson (2001) showing that "the most important factor affecting supertree performance is, ironically, the most attractive feature of the method: the ability to combine trees with nonidentical taxon sets." We therefore agree with Gatesy et al (2004) who indicated that to address unsolved classification questions systematists should collect new character data rather than to make a supertree with limited data from the taxa of interest.
The core cantharelloid clade. Cantharellus and Craterellus.— –
The distinction between the genera Cantharellus and Craterellus (which collectively include about 90 described species) has long been disputed (Petersen 1971). Different authors classified some species in one genus or the other depending on which morphological characters were emphasized. Dahlman et al (2000) showed that these two genera can be distinguished based on nLSU and ITS sequences and that the presence of a hollow stipe seems to be a morphological synapomorphy for Craterellus. Results from the present study are in agreement with Dahlman et al (2000) and support a sister-group relationship between these two genera. Within Craterellus five species or species complexes can be recognized among northern temperate taxa: the Cr. cornucopioides complex (including Cr. fallax and Cr. konradii), the Cr. tubaeformis complex (including Cr. infundibuliformis), Cr. odoratus, Cr. lutescens, and Cr. ignicolor (Dahlman et al 2000).
A molecular phylogenetic study in Cantharellus was produced by Dunham et al (2003) from the use of nLSU and ITS data. Our four-gene phylogeny was in full agreement with the findings of these authors and supported the distinction between C. cascadensis, C. formosus, C. subalbidus, C. persicinus, C. lateritius and C. cibarius. Our tree (FIG. 1C) and other evidence (Moncalvo and Dunham unpublished) suggest the presence of several cryptic geographic species within the C. cibarius complex sensu stricto. A novel finding of this study is that two smaller, slender "yellow chanterelles", C. appalachiensis and C. minor, are more closely related to the red species of the C. cinnabarinus group than they are to the core group of yellow chanterelles.
Hydnum and the Sistotrema confluens group.— –
Hydnum is a morphologically well defined genus that includes about 120 described species characterized by fleshy fruiting bodies with a toothed or spinose hymenophore and pale, smooth spores. This genus, represented in our dataset by 11 strains representing at least seven species, was monophyletic in all our analyses. Two closely related species commonly reported throughout the northern hemisphere, H. repandum and H. rufescens, were not found to be respectively monophyletic and warrant further comparative taxonomic scrutiny from a global geographic sampling (FIG. 1B).
Strongly clustering with Hydnum in the nLSU analyses were Sistotrema confluens, S. alboluteum and S. muscicola (FIG. 1B). These species (along with S. dennisii, not sampled here) are distinguished from other Sistotrema species by the presence of a irpicoidporoid hymenophore (sometime almost hydnoid in the case of S. confluens), globose to subglobose spores and lack of cystidia (Eriksson et al 1984). The placement of S. confluens and S. muscicola close to Hydnum was indicated already in Larsson et al (2004). Our two samples of S. muscicola were quite divergent (SUPPLEMENTARY FIG. 1). According to Eriksson et al (1984) much controversy still surrounds the true identity and circumscription of S. muscicola, which should only be regarded as a "form-complex". Based on their phylogenetic affinities, we suspect these Sistotrema species to be ectomycorrhizal.
Phylogenetic relationships among the chanterelles, Hydnum and the S. confluens group remained unclear. In the all-taxa four-gene analyses (SUPPLEMENTARY FIG. 1), the Bayesian tree strongly supported Hydnum as the sister group of Cantharellus-Craterellus (Bayesian posterior probability [pp] = 1) while parsimony bootstrapping suggested S. confluens as the sister group (88% bootstrap support [bs]).
Sistotrema traditionally has been regarded as a relatively well delimited genus of wood saprophytes characterized by the presence of urniform basidia generally bearing 6–8 sterigmata, but species limits are often unclear (Eriksson et al 1984). Most Sistotrema species have a corticioid habit with a smooth or somewhat irregularly poroid or irpicoid-hydnoid hymenophore, but some species develop sporocarps that mimic the dimidiate or stipitate habits. Results from our analyses clearly demonstrated that Sistotrema is highly polyphyletic (FIG. 1A–B). Nonmonophyly of this genus already was suggested in the studies of Larsson et al (2004) and Binder et al (2005).
Sistotrema is polyphyletic.— – Phylogenetic relationships of Sistotrema species with an irpicioid-poroid hymenium (S. confluens, S. alboluteum, S. muscicola) to Hydnum was discussed above. Because S. confluens is the type species of the genus, the species presented below are in need of nomenclatural revision. Our analyses revealed three monophyletic groups (the S. brinkmannii-oblongisporum clade, the S. eximum-octosporum clade and S. adnatum-coronilla) and left two species with unresolved phylogenetic affinities (S. raduloides and S. athelioides).
S. brinkmannii, S. farinaceum, S. resinicystidium and S. oblongisporum form a monophyletic group (FIG. 1B), but there is no obvious morphological synapomorphy to arrange these taxa together. The morphological species S. brinkmannii was found to consist of an aggregate of biological species (Lemke 1969, Ullrich and Raper 1975, Hallenberg 1984). This is concordant with our tree (FIG. 1B) that shows nonmonophyly of isolates that were identified morphologically as S. brinkmannii, which mixed with strains labeled S. oblongisporum. The sequence labeled Sistotremastrum niveocremeum that nested in this group represents a misidentification; the true Sistotremastrum niveocremeum belongs to the trechisporoid clade (Binder et al 2005, Larsson unpublished).
Another monophyletic group consisted of S. eximum, S. efibulatum, S. sernanderi, S. biggsiae and S. octosporum (FIG. 1B). No obvious morphological evidence groups these taxa together (Eriksson et al 1984). Our analyses also indicated monophyly of strains labeled S. adnatum and S. coronilla, which clustered with the S. eximum group in the nLSU analyses (FIG. 1B) but not in the all-taxa four-gene analyses (SUPPLEMENTARY FIG. 1). S. coronilla was noted as a doubtful species by Eriksson et al (1984) and sometimes was listed as a synonym of S. brinkmannii. Weakly clustering with S. adnatum and S. coronilla was a sequence labeled Tricellulortus peponiformis (AY004068
[GenBank]
, Platas et al unpublished; correct genus name is Pneumatospora). This species represents a monotypic anamorphic genus classified in the Basidiomycota in the Index of Fungi (http://www.indexfungorum.org) but listed as a mitosporic ascomycete in the NCBI taxonomic database (http://www.ncbi.nlm.nih.gov). Further investigation on the identity and phylogenetic relationships of this poorly known taxon is needed.
Our analyses placed Sistotrema raduloides and S. athelioides in more basal, unresolved position in the cantharelloid clade sensu stricto (FIG. 1A–B). S. raduloides is a circumboreal species forming extended, distinctly hydnoid sporocarps, preferably on dead aspen logs. S. athelioides is known only from one locality on Vancouver Island, British Columbia, and was described as one of many genetically distinct forms within the S. brinkmannii complex (Hallenberg 1984). The fact that these two species clustered separately from the other Sistotrema species further demonstrated the high heterogeneity of the genus.
Overall our results demonstrate the need for a more detailed study of the urniform-bearing basidia genus "Sistotrema", which appears to be a polyphyletic assemblage of essentially resupinate forms from which coralloid, hydnoid and agaricoid sporocarps have evolved.
Clavulina and Membranomyces.— –
The coralloid genus Clavulina is characterized by branched basidiomata and contains at least 50 species worldwide, primarily in the tropics (Henkel et al 2005). It traditionally was segregated from other coral fungi by the presence of cornute, bisterigmate basidia (Corner 1950, Petersen 1988). However neotropical species with unbranching basidiomata and/or forming infundibuliform rather than coralloid basidiomes and/or bearing 4–6 spores per basidium recently were described and their classification in Clavulina was supported by nLSU sequence data (Thacker and Henkel 2004, Henkel et al 2005). The placement of Clavulina in the cantharelloid clade first was indicated by Hibbett et al (1997) and substantiated in several subsequent studies. Here we sampled more broadly within this genus and confirm the monophyly of Clavulina sensu Henkel and collaborators and indicate that this genus is sister of the S. brinkmannii-oblongisporum clade (FIG. 1A–B).
The small corticioid genus Membranomyces (two spp.) exhibits cylindrical basidia with cornute sterigmata, and subglobose, smooth, slightly thick-walled spores as Clavulina. Based on these similarities Parmasto proposed the transfer of this corticiaceous genus to the Clavulinaceae (Eriksson and Ryvarden 1973). Our results indicate a sister relationship between Clavulina and Membranomyces (FIG. 1B) as in Larsson et al (2004) and Binder et al (2005). However this assumption still is based solely on a single nLSU sequence of Membranomyces delectabilis (AY586688
[GenBank]
, Larsson et al 2004). This species originally was referred to the genus Clavulicium that is typified by Clavulicium macounii. Jülich (1975) questioned this generic arrangement and created Membranomyces to segregate simple-septate species. Molecular data support that decision because Clavulicium does not belong to the cantharelloid clade although its phylogenetic position still is unresolved (K-H Larsson unpublished).
Multiclavula.— –
The small, lichenized club-mushroom genus Multiclavula currently consists of 12 accepted species (Index of Fungi). This genus has been found affiliated with cantharelloid taxa in many previous molecular phylogenetic studies, but its position within the clade has remained unclear. Here we present the first evidence that Multiclavula is the sister group of Clavulina and the S. brinkmannii-oblongisporum clade (FIG. 1A–B).
Botryobasidium.— –
Species of the saprophytic genus Botryobasidium have corticioid to hypochnoid resupinate basidiocarps and characteristic basidia that are short, cylindrical or subcylindrical to suburniform with 2–8 sterigmata, and generally arranged in clusters (Eriksson and Ryvarden 1973). Anamorphic stages are known and were described in Haplotrichum or Allescheriella. Botryobasidium was monographed by Langer (1994), who accepted 48 species in the genus. Parmasto et al (2004) similarly recognized 50 species. Relationships among Botryobasidium, Sistotrema, the Ceratobasidiaceae and Tulasnella have long been suggested and debated (Martin 1948; Donk 1956, 1972; Parmasto 1968; Eriksson and Ryvarden 1973; Jülich 1981). These taxa share similar short or urniform basidia that also often deviate from the 4-sterigmata type that is common to most homobasidiomycetes.
The first molecular evidence of a close phylogenetic relationship between Botryobasidium and Cantharellus was presented by Hibbett et al (1997). Here we sampled sequence data from 17 members of Botryobasidium representing at least 10 species (SUPPLEMENTARY TABLE I and FIG. 1D). Monophyly of this genus was supported strongly (100% bs/pp = 1), in agreement with Binder et al (2005) who sampled 11 isolates from this genus. Our four-gene analyses suggested that Botryobasidium is a sister group of the core cantharelloid clade (FIG. 1A). It also appears that the taxonomic identity of, and distinction among, B. candicans, B. botryosum and B. simile are problematic (FIG. 1D), as pointed by Eriksson and Ryvarden (1973).
The Ceratobasidiaceae.— –
A major problem in the phylogeny of Hymenomycetes concerns the placements of the Ceratobasidiaceae ( = Ceratobasidiales sensu Roberts 1999), Tulasnellales and Sebacinales (Hibbett 2003). The Ceratobasidiaceae includes the genera Ceratobasidium, Thanatephorus, Uthatobasidium, Waitea and Marchandiobasidium, which presently are composed of respectively 21, nine, two, two and one recognized species (Index of Fungi). These corticioid taxa are united by the presence of a perforate parenthesome with large openings. Also, except in the small genera Waitea and Marchandiobasidium and in a few Thanatephorus species, these taxa form secondary spores (or "spore germinating by repetition") from primary spores born on short, often urniform holobasidia (Roberts 1999, Diederich et al 2003, Weiß et al 2004a). The formation of secondary spores is a well known phenomenon in the heterobasidiomycetes but is not observed in typical homobasidiomycetes. This particular feature led Donk (1964, 1972) and others (e.g. Eriksson and Ryvarden 1973) to link Ceratobasidium to the heterobasidiomycetes, particularly to Tulasnella. However the 2–8-sterigmate and urniform basidia along with the corticioid habit deterred these authors from decisively separating these taxa from Sistotrema, Botryobasidium and the Corticiaceae sensu lato.
Marchandiobasidium is a sclerotium-producing lichenicolous fungus that recently was segregated from the form-genus Marchandiomyces and classified in the Ceratobasidiales by Diederich et al (2003), in part because they noted that the unidentified nSSU sequence clustering with a Thanatephorus sequence in Sikaroodi et al (2001) corresponds to Marchandiobasidium aurantiacus. The SSU phylogeny presented in Sikaroodi et al (2001) also placed the anamorph of the type of Waitea, Rhizoctonia zeae, in an unresolved position but well separated from Thanatephorus. Waitea was placed with Piloderma at the base of the Agaricales in Bruns et al (1998). These results suggest that Waitea does not belong to the Ceratobasidiaceae.
Overall it appears that the Ceratobasidiales sensu Roberts (1999) is probably polyphyletic. The core taxa of the traditional Ceratobasidiaceae (Ceratobasidium, Thanatephorus and Uthatobasidium) however seem to represent a monophyletic group that belongs to the cantharelloid clade (see below). But the taxonomic situation is complicated by the fact that the type species of Ceratobasidium (C. calosporum) has a dolipore with an imperforate parenthesome, whereas the ultrastructural circumscription of the Ceratobasidiales by Roberts (1999) was based on the presence of perforated parenthesomes with large openings (Weiß et al 2004a). A major problem in dealing with the systematics of these fungi is that accurate taxonomic identification is difficult using morphology alone. In addition DNA sequence sampling for members of this group still is limited to a few isolates.
Here we used Ceratobasidiaceae sequences available from public databases and found that they form a monophyletic group that is sister of both Botryobasidium and members of the core cantharelloid clade (FIG. 1A). Our results also showed that the distinction between Uthatobasidium and Ceratobasidium is not clear-cut (FIG. 1D) and will need further investigation. Also Thanatephorus mainly was distinguished from Uthatobasidium for being parasitic on herbaceous plants and its connection to Rhizoctonia anamorphs (Hjortstam et al 1988), but a recent molecular phylogenetic study by Gonzalez et al (2001) showed that Rhizoctonia anamorphs are associated with both Ceratobasidium and Thanatephorus teleomorphs. In summary much more work is required to resolve evolutionary relationships and taxonomic concepts within the Ceratobasidiaceae/Ceratobasidiales.
Tulasnella.— –
The traditional heterobasidiomycete genus Tulasnella and related taxa (Tulasnellaceae or Tulasnellales) consist of resupinate forms characterized by unique basidia with swollen septate epibasidia in place of sterigmata, which produce secondary spores by the process of germinating by repetition. The genus currently includes 47 described species (Index of Fungi) and many Rhizoctonia anamorphs (Roberts 1999). Tulasnella forms plant ectomycorrhizae and mycorrhiza-like associations with liverworts (Bidartondo et al 2003, Kottke et al 2003) and also is associated with orchid roots along with other Rhizoctonia-forming fungi with teleomorphs in the Ceratobasidiaceae and Sebacinales (Rasmussen 1995, Roberts 1999, Kristiansen et al 2001, Taylor et al 2003, Bidartondo et al 2004, Shefferson et al 2005).
Tulasnella first was proposed to be a member of the cantharelloid clade in Hibbett and Thorn (2001). This placement was confirmed in later studies that used nuclear rDNA sequences (e.g. Bidartondo et al 2003, Kottke et al 2003, Weiß et al 2004, Binder et al 2005), but its exact position within that clade remained unclear. Problems associated with high rate of molecular evolution in Tulasnella nuclear rDNA genes have been discussed above (and in SUPPLEMENT). Here we showed that mtSSU, and more robustly RPB2, sequence data placed Tulasnella as a sister group of all the taxa presented above. This inferred phylogenetic position, along with both morphological (resupinate habit and spore germination with repetition) and ecological (Rhizoctonia-type orchid association) evidences, collectively support the placement of Tulasnella in a more basal position in the cantharelloid clade, in the vicinity of Ceratobasidiaceae. Such placement also agrees with the non-monophyly of the heterobasidiomycetes as it appeared from recent studies (Weiß and Oberwinkler 2001; Weiß et al 2004a, b; Lutzoni et al 2004; Matheny and Hibbett unpublished). It also reconciles the dilemma of past authors about the relationships among Ceratobasidiaceae, Botryobasidium and Tulasnella, as discussed in Eriksson and Ryvarden (1973:219).
Sebacinales.— –
Sebacinales (Weiß et al 2004b) are traditional heterobasidiomycetes with longitudinally septate exidioid basidia (Wells and Oberwinkler 1982). Members of this order are involved in a wide spectrum of mycorrhizal associations with plants and liverworts (Rasmussen 1995; Roberts 1999; Kristiansen et al 2001; Taylor et al 2003; Bidartondo et al 2003, 2004; Kottke et al 2003; Taylor et al 2003; Weiß et al 2004b; Setaro et al 2006). Our analyses support monophyly of the Sebacinales (represented here with the genera Sebacina, Serendipita, Craterocolla, Piriformospora and Tremellodendron) as in Weiß and Oberwinkler (2001) and Weiß et al (2004a, b). While the present study supports the inclusion of the Ceratobasidiaceae and possibly also Tulasnella in the cantharelloid clade, our results show no evidence to place the Sebacinales in that clade. In the all-taxa four-gene analyses, our representatives of the Sebacinales (Piriformospora indica and Tremellodendron pallidum) strongly clustered with Gautieria (representing the gomphoid-phalloid clade) and Auricularia (a traditional heterobasidiomycete) when the tree is rooted with Dacrymyces (heterobasidiomycetes). The latter relationships should be taken with much caution because in this study our sampling of gomphoid-palloid and heterobasidiomycetes was limited.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSRESULTS AND DISCUSSIONCONCLUSIONLITERATURE CITED |
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). A possible synapomorphy for this clade could be the stichic type of nuclear division (Hibbett and Thorn 2001, Larsson et al 2004) that was found in Cantharellus, Craterellus, Clavulina, Membranomyces and Hydnum (Penancier 1961). However information about the nuclear division type in Sistrotrema, Botryobasidium and Ceratobasidiaceae still is lacking. Tulasnella species display chiastic nuclear division (Penancier 1961). This cytological character reinforces the mtSSU and RPB2 phylogenies displacing Tulasnella from Cantharellus-Craterellus and the core cantharelloid group, in conflict with rDNA data (SUPPLEMENTARY FIG. 1). Parenthesome ultrastructure has been considered a possible character for recognizing major basidiomycete lineages (Clémençon 1997). Perforate parenthesomes are found commonly in the homobasidiomycetes, while imperforate parenthesomes characterize the traditional heterobasidiomycetes (e.g. Dacrymycetales, Auriculariales, Sebacinales and Tulasnellales). Imperforate parenthesomes however also occur in several members of the gomphoid-phalloid, hymenochaetoid, trechisporoid and cantharelloid clade. In the cantharelloid clade imperforate parenthesomes have been found in Cantharellus and Botryobasidium, but perforate parenthesomes have been reported from Ceratobasidiales (except for the type species of Ceratobasidium, see above) and Sistotrema brinkmannii (Langer 1994, Hibbett and Thorn 2001, Weiß and Oberwinkler 2001, Diederich et al 2003, Larsson et al 2004, Bianchinotti et al 2005). Therefore no single parenthesome type unites members of the cantharelloid clade.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 Corresponding author. E-mail: jeanmarcm{at}gmail.com
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