Archiascomycetes: detection of a major new lineage within the Ascomycota

A novel Arabidopsis phyllosphere resident Protomyces species and a re-examination of genus Protomyces based on genome sequence data

Protomyces is an understudied genus of yeast-like fungi currently defined as phytopathogens of only Umbelliferae and Compositae. Species relationships and boundaries remain controversial and molecular data are lacking. Of the 82 named Protomyces, we found few recent studies and six available cultures. We previously isolated Protomyces strains from wild Arabidopsis thaliana, a member of Brassicaceae, a family distant from accepted Protomyces hosts. We previously sequenced the genomes of all available Protomyces species, and P. arabidopsidicola sp. nov. strain C29, from Arabidopsis. Phylogenomics suggests this new species occupied a unique position in the genus. Genomic, morphological, and physiological characteristics distinguished P. arabidopsidicola sp. nov. from other Protomyces. Nuclear gene phylogenetic marker analysis suggests actin1 gene DNA sequences could be used with nuclear ribosomal DNA internal transcribed spacer sequences for rapid identification of Protomyces species. Previous studies demonstrated P. arabidopsidicola sp. nov. could persist on the Arabidopsis phyllosphere and Protomyces sequences were discovered on Arabidopsis at multiple sites in different countries. We conclude that the strain C29 represents a novel Protomyces species and propose the name of P. arabidopsidicola sp. nov. Consequently, we propose that Protomyces is not strictly associated only with the previously recognized host plants.

Novakomyces olei sp. nov., the First Member of a Novel Taphrinomycotina Lineage

Taphrinomycotina is the smallest subphylum of the phylum Ascomycota. It is an assemblage of distantly related early diverging lineages of the phylum, comprising organisms with divergent morphology and ecology; however, phylogenomic analyses support its monophyly. In this study, we report the isolation of a yeast strain, which could not be assigned to any of the currently recognised five classes of Taphrinomycotina. The strain of the novel budding species was recovered from extra virgin olive oil and characterised phenotypically by standard methods. The ultrastructure of the cell wall was investigated by transmission electron microscopy. Comparisons of barcoding DNA sequences indicated that the investigated strain is not closely related to any known organism. Tentative phylogenetic placement was achieved by maximum-likelihood analysis of the D1/D2 domain of the nuclear LSU rRNA gene. The genome of the investigated strain was sequenced, assembled, and annotated. Phylogenomic analyses placed it next to the fission Schizosaccharomyces species. To accommodate the novel species, Novakomyces olei, a novel genus Novakomyces, a novel family Novakomycetaceae, a novel order Novakomycetales, and a novel class Novakomycetes is proposed as well. Functional analysis of genes missing in N. olei in comparison to Schizosaccharomyces pombe revealed that they are biased towards biosynthesis of complex organic molecules, regulation of mRNA, and the electron transport chain. Correlating the genome content and physiology among species of Taphrinomycotina revealed some discordance between pheno- and genotype. N. olei produced ascospores in axenic culture preceded by conjugation between two cells. We confirmed that N. olei is a primary homothallic species lacking genes for different mating types.

A Molecular Window into the Biology and Epidemiology of Pneumocystis spp

Pneumocystis, a unique atypical fungus with an elusive lifestyle, has had an important medical history. It came to prominence as an opportunistic pathogen that not only can cause life-threatening pneumonia in patients with HIV infection and other immunodeficiencies but also can colonize the lungs of healthy individuals from a very early age. The genus Pneumocystis includes a group of closely related but heterogeneous organisms that have a worldwide distribution, have been detected in multiple mammalian species, are highly host species specific, inhabit the lungs almost exclusively, and have never convincingly been cultured in vitro, making Pneumocystis a fascinating but difficult-to-study organism. Improved molecular biologic methodologies have opened a new window into the biology and epidemiology of Pneumocystis. Advances include an improved taxonomic classification, identification of an extremely reduced genome and concomitant inability to metabolize and grow independent of the host lungs, insights into its transmission mode, recognition of its widespread colonization in both immunocompetent and immunodeficient hosts, and utilization of strain variation to study drug resistance, epidemiology, and outbreaks of infection among transplant patients. This review summarizes these advances and also identifies some major questions and challenges that need to be addressed to better understand Pneumocystis biology and its relevance to clinical care.

Changes in nucleosome formation at gene promoters in the archiascomycetous yeast Saitoella complicata

We measured the degree of nucleosome formation at the gene promoters in trichostatin A-treated (1, 2, and 3 µg/mL) cells of the archiascomycete Saitoella complicata and those in enlarged S. complicata cells after zymolyase treatment. TSA-treated and enlarged cells showed similar changes in nucleosome occupancy in five out of six positions in the gene promoters. These results suggest that changes in nucleosome formation at the gene promoters could serve as stress response mechanisms elicited in response to spheroplast (zymolyase treatment) and TSA treatment. In addition, we demonstrated that changes in nucleosome position occurred mainly in cells treated with 1 µg/mL TSA, whereas cells treated with 2 and 3 µg/mL TSA did not exhibit significant changes in the degree of nucleosome formation.

Draft Genome Sequence of the Archiascomycetous Yeast Saitoella complicata

The draft genome sequence of the archiasomycetous yeast Saitoella complicata was determined. The assembly of newly and previously sequenced data sets resulted in 104 contigs (total of 14.1 Mbp; N₅₀, 239 kbp). On the newly assembled genome, a total of 6,933 protein-coding sequences (7,119 transcripts, including alternative splicing forms) were identified.

Ascomycete fungal actins differentially support plant spatial cell and organ development

Actin interacts with a wide variety of cytoplasmic and nuclear proteins to support spatial development in nearly all eukaryotes. Null mutations in plant vegetative actins produce dramatically altered cell, tissue, and organ morphologies. Animal cytoplasmic actins (e.g., human HsACTB, HsACTG1) and some ancestral protist actins fully suppress these mutant phenotypes suggesting that some animal, plant, and protist actins share functional competence for spatial development. Considering that fungi have a phylogenetic origin closer to animals than plants, we were interested to explore whether the fungal actins may have this same capacity to function in plants and support development. We ectopically expressed actins from four highly divergent ascomycete fungi in two different Arabidopsis double vegetative actin null mutants. We found that expression of actin from the earliest diverging ascomycete subphyla, the archiascomycete Schizosaccharomyces pombe, qualitatively and quantitatively suppressed the root cell polarity and root organ developmental defects of act8/act7 mutants and the root-hairless cell elongation phenotype of act2/act8 mutants. Interestingly, the actin from the pyrenomycete Neurospora crassa was modestly effective in the suppression of vegetative actin mutant phenotypes. In contrast, actins from the saccharomycetes Saccharomyces cerevisiae and Candida albicans were unable to support any aspect of plant development, and moreover induced severe dwarfism and sterility. These data imply that basal fungi inherited an actin with full competence for spatial development from their protist ancestor and maintained it via non-progressive sequence evolution, while the later more derived fungal species lost these activities.

Distribution of introns in fungal histone genes

Saccharomycotina and Taphrinomycotina lack intron in their histone genes, except for an intron in one of histone H4 genes of Yarrowia lipolytica. On the other hand, Basidiomycota and Perizomycotina have introns in their histone genes. We compared the distributions of 81, 47, 79, and 98 introns in the fungal histone H2A, H2B, H3, and H4 genes, respectively. Based on the multiple alignments of the amino acid sequences of histones, we identified 19, 13, 31, and 22 intron insertion sites in the histone H2A, H2B, H3, and H4 genes, respectively. Surprisingly only one hot spot of introns in the histone H2A gene is shared between Basidiomycota and Perizomycotina, suggesting that most of introns of Basidiomycota and Perizomycotina were acquired independently. Our findings suggest that the common ancestor of Ascomycota and Basidiomycota maybe had a few introns in the histone genes. In the course of fungal evolution, Saccharomycotina and Taphrinomycotina lost the histone introns; Basidiomycota and Perizomycotina acquired other introns independently. In addition, most of the introns have sequence similarity among introns of phylogenetically close species, strongly suggesting that horizontal intron transfer events between phylogenetically distant species have not occurred recently in the fungal histone genes.

A fungal phylogeny based on 82 complete genomes using the composition vector method

BACKGROUND

Molecular phylogenetics and phylogenomics have greatly revised and enriched the fungal systematics in the last two decades. Most of the analyses have been performed by comparing single or multiple orthologous gene regions. Sequence alignment has always been an essential element in tree construction. These alignment-based methods (to be called the standard methods hereafter) need independent verification in order to put the fungal Tree of Life (TOL) on a secure footing. The ever-increasing number of sequenced fungal genomes and the recent success of our newly proposed alignment-free composition vector tree (CVTree, see Methods) approach have made the verification feasible.

RESULTS

In all, 82 fungal genomes covering 5 phyla were obtained from the relevant genome sequencing centers. An unscaled phylogenetic tree with 3 outgroup species was constructed by using the CVTree method. Overall, the resultant phylogeny infers all major groups in accordance with standard methods. Furthermore, the CVTree provides information on the placement of several currently unsettled groups. Within the sub-phylum Pezizomycotina, our phylogeny places the Dothideomycetes and Eurotiomycetes as sister taxa. Within the Sordariomycetes, it infers that Magnaporthe grisea and the Plectosphaerellaceae are closely related to the Sordariales and Hypocreales, respectively. Within the Eurotiales, it supports that Aspergillus nidulans is the early-branching species among the 8 aspergilli. Within the Onygenales, it groups Histoplasma and Paracoccidioides together, supporting that the Ajellomycetaceae is a distinct clade from Onygenaceae. Within the sub-phylum Saccharomycotina, the CVTree clearly resolves two clades: (1) species that translate CTG as serine instead of leucine (the CTG clade) and (2) species that have undergone whole-genome duplication (the WGD clade). It places Candida glabrata at the base of the WGD clade.

CONCLUSION

Using different input data and methodology, the CVTree approach is a good complement to the standard methods. The remarkable consistency between them has brought about more confidence to the current understanding of the fungal branch of TOL.

Widespread occurrence and phylogenetic placement of a soil clone group adds a prominent new branch to the fungal tree of life

Fungi are one of the most diverse groups of Eukarya and play essential roles in terrestrial ecosystems as decomposers, pathogens and mutualists. This study unifies disparate reports of unclassified fungal sequences from soils of diverse origins and anchors many of them in a well-supported clade of the Ascomycota equivalent to a subphylum. We refer to this clade as Soil Clone Group I (SCGI). We expand the breadth of environments surveyed and develop a taxon-specific primer to amplify 2.4kbp rDNA fragments directly from soil. Our results also expand the known range of this group from North America to Europe and Australia. The ancient origin of SCGI implies that it may represent an important transitional form among the basal Ascomycota groups. SCGI is unusual because it currently represents the only major fungal lineage known only from sequence data. This is an important contribution towards building a more complete fungal phylogeny and highlights the need for further work to determine the function and biology of SCGI taxa.

Evolution of nematode-trapping cells of predatory fungi of the Orbiliaceae based on evidence from rRNA-encoding DNA and multiprotein sequences

Among fungi, the basic life strategies are saprophytism, parasitism, and predation. Fungi in Orbiliaceae (Ascomycota) prey on animals by means of specialized trapping structures. Five types of trapping devices are recognized, but their evolutionary origins and divergence are not well understood. Based on comprehensive phylogenetic analysis of nucleotide sequences of three protein-coding genes (RNA polymerase II subunit gene, rpb2; elongation factor 1-alpha gene, ef1-alpha; and ss tubulin gene, bt) and ribosomal DNA in the internal transcribed spacer region, we have demonstrated that the initial trapping structure evolved along two lineages yielding two distinct trapping mechanisms: one developed into constricting rings and the other developed into adhesive traps. Among adhesive trapping devices, the adhesive network separated from the others early and evolved at a steady and gentle speed. The adhesive knob evolved through stalk elongation, with a final development of nonconstricting rings. Our data suggest that the derived adhesive traps are at a highly differentiated stage. The development of trapping devices is felicitous proof of adaptive evolution.

A higher-level phylogenetic classification of the Fungi

A comprehensive phylogenetic classification of the kingdom Fungi is proposed, with reference to recent molecular phylogenetic analyses, and with input from diverse members of the fungal taxonomic community. The classification includes 195 taxa, down to the level of order, of which 16 are described or validated here: Dikarya subkingdom nov.; Chytridiomycota, Neocallimastigomycota phyla nov.; Monoblepharidomycetes, Neocallimastigomycetes class. nov.; Eurotiomycetidae, Lecanoromycetidae, Mycocaliciomycetidae subclass. nov.; Acarosporales, Corticiales, Baeomycetales, Candelariales, Gloeophyllales, Melanosporales, Trechisporales, Umbilicariales ords. nov. The clade containing Ascomycota and Basidiomycota is classified as subkingdom Dikarya, reflecting the putative synapomorphy of dikaryotic hyphae. The most dramatic shifts in the classification relative to previous works concern the groups that have traditionally been included in the Chytridiomycota and Zygomycota. The Chytridiomycota is retained in a restricted sense, with Blastocladiomycota and Neocallimastigomycota representing segregate phyla of flagellated Fungi. Taxa traditionally placed in Zygomycota are distributed among Glomeromycota and several subphyla incertae sedis, including Mucoromycotina, Entomophthoromycotina, Kickxellomycotina, and Zoopagomycotina. Microsporidia are included in the Fungi, but no further subdivision of the group is proposed. Several genera of 'basal' Fungi of uncertain position are not placed in any higher taxa, including Basidiobolus, Caulochytrium, Olpidium, and Rozella.

The new higher level classification of eukaryotes with emphasis on the taxonomy of protists

This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional "kingdoms." The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.

Pneumocystis and Trypanosoma cruzi: Nomenclature and Typifications

Published phylogenetic reclassifications of Pneumocystis as a fungus resulted in a nomenclatural shift from the Zoological Code to the International Code of Botanical Nomenclature. The same may be true for all microsporidians and sundry other organisms. This resulted in the invalidation of names and subsequently precipitated changes to the botanical code to accommodate Pneumocystis and microsporidian names. The repercussions following application of the 2005 Vienna Code to Pneumocystis nomenclature are detailed. Validity of the name for the human pathogen, Pneumocystis jirovecii, is re-established from its 1976 publication under the Zoological Code, contrary to interpretation of validity under earlier botanical codes. Pneumocystis jirovecii is lectotypified and epitypified. The rat parasite, Pneumocystis carinii, is neotypified, separating it from Pneumocystis wakefieldiae. The original 1909 description of Trypanosoma cruzi, type species for Schizotrypanum, and causal agent of Chagas' disease, included parts of the life cycle of Pneumocystis. Trypanosoma cruzi is neotypified by the true Trypanosoma elements, thereby completing the nomenclatural separation from Pneumocystis and ensuring that Schizotrypanum is not applicable to Pneumocystis as an earlier name. The neotypes for P. carinii and T. cruzi represent the strains currently being investigated by their two respective genome projects. They were selected in light of their medical importance, physiological characterizations, and absence of lectotypifiable materials. The classification and nomenclature of Pneumocystis is reviewed and guidelines given for the publication of new species.

Phylogeny and evolution of medical species of Candida and related taxa: a multigenic analysis

Hemiascomycetes are species of yeasts within the order Saccharomycetales. The order encompasses disparate genera with a variety of life styles, including opportunistic human pathogens (e.g., Candida albicans), plant pathogens (e.g., Eremothecium gossypii), and cosmopolitan yeasts associated with water and decaying vegetation. To analyze the phylogeny of medically important species of yeasts, we selected 38 human pathogenic and related strains in the order Saccharomycetales. The DNA sequences of six nuclear genes were analyzed by maximum likelihood and Bayesian phylogenetic methods. The maximum likelihood analysis of the combined data for all six genes resolved three major lineages with significant support according to Bayesian posterior probability. One clade was mostly comprised of pathogenic species of Candida. Another major group contained members of the family Metschnikowiaceae as a monophyletic group, three species of Debaryomyces, and strains of Candida guilliermondii. The third clade consisted exclusively of species of the family Saccharomycetaceae. Analysis of the evolution of key characters indicated that both codon reassignment and coenzyme Q(9) likely had single origins with multiple losses. Tests of correlated character evolution revealed that these two traits evolved independently.

Molecular phylogeny of Zygomycota based on EF-1alpha and RPB1 sequences: limitations and utility of alternative markers to rDNA

Earlier molecular phylogenetic analyses based on nuclear small subunit ribosomal DNA (nSSU rDNA) suggest that the Zygomycota are polyphyletic within the Chytridiomycota. However, these analyses failed to resolve almost all interordinal relationships among basal fungi (Chytridiomycota and Zygomycota), due to lack of sufficient characters within the nSSU rDNA. To further elucidate the higher-level phylogeny of Zygomycota, we have sequenced partial RPB1 (DNA dependent RNA polymerase II largest subunit) and EF-1alpha (translation elongation factor 1 alpha) genes from 10 and 3 zygomycete fungi, respectively. Independent molecular phylogenetic analyses were performed based on each sequence by distance and maximum likelihood methods. Although deep phylogenetic relationships among basal fungi still remain poorly resolved using either gene, the RPB1-based phylogeny identified a novel monophyletic clade consisting of the Dimargaritales, Harpellales, and Kickxellales. This result suggests that regularly formed septa (cross walls that divide hyphae into segments) with a lenticular cavity are plesiomorphic for this clade, and indicates the importance of septal pore ultrastructure in zygomycete phylogeny. In addition, a peculiar mucoralean genus Mortierella, which was considered to be distantly related to the other Mucorales based on previous nSSU rDNA analyses, was resolved as the basal most divergence within the Mucorales, consistent with traditional phenotypic-based taxonomy. Although the taxa included in our analysis are restricted, the monophyly of each order suggested by nSSU rDNA phylogeny is supported by the present RPB1-based analysis. These results support the potential use of RPB1 as an alternative marker for fungal phylogenetic studies. Conversely, the overall fungal phylogeny based on EF-1alpha sequence is poorly resolved. A comparison of numbers of observed substitutions versus inferred substitutions within EF-1alpha indicates that this gene is much more saturated than RPB1. This result suggests that the EF-1alpha gene is unsuitable for resolving higher-level phylogenetic relationships within the Fungi.

Isolation of a CDC28 homologue from Cryptococcus neoformans that is able to complement cdc28 temperature-sensitive mutants of Saccharomyces cerevisiae

A partial cDNA fragment of the Cryptococcus neoformans homologue of the main cell cycle control gene CDC28/cdc2 was isolated using degenerate primer RT-PCR. A subsequent search in the C. neoformans genome database identified several sequences similar to CDC28/cdc2. A part of the sequence which showed the highest similarity to CDC28/cdc2 turned out to be identical to the partial cyclin-dependent kinase (Cdk) cDNA fragment isolated by degenerate RT-PCR. The full-length coding region of this Cdk homologue was amplified by RT-PCR using primers designed to target regions around start and stop codons, and the gene was named CnCdk1. To determine its function, an analysis of deduced amino acid sequence of the CnCdk1 was performed and its ability to rescue Saccharomyces cerevisiae cdc28-temperature sensitive mutants was tested. S. cerevisiae cdc28-4 and cdc28-1N strains transformed with the pYES2- CnCdk1 construct exhibited growth at 36.5 degrees C in galactose-raffinose medium, but not in glucose medium. Results of the sequence analysis and the fact that CnCdk1 is able to complement the S. cerevisiae cdc28-ts mutation support its assumed role as the CDC28/cdc2 homologue in C. neoformans.

Body plan evolution of ascomycetes, as inferred from an RNA polymerase II phylogeny

The mode of evolution of the biologically diverse forms of ascomycetes is not well understood, largely because the descent relationships remain unresolved. By using sequences of the nuclear gene RPB2, we have inferred with considerable resolution the phylogenetic relationships between major groups within the phylum Ascomycota. These relationships allow us to deduce a historical pattern of body plan evolution. Within Taphrinomycotina, the most basal group, two simple body plans exist: uncovered asci with unicellular growth, or rudimentary ascoma with hyphal growth. Ancestral ascomycetes were filamentous; hyphal growth was lost independently in the yeast forms of Taphrinomycotina and Saccharomycotina. Pezizomycotina, the sister group to Saccharomycotina, retained mycelial growth while elaborating two basic ontogenetic pathways for ascoma formation and centrum development. The RPB2 phylogeny shows with significant statistical support that taxa in Pezizomycotina with ascohymenial ontogeny (ascoma generally forms after nuclear pairing) are ancestral and paraphyletic, whereas ascolocular fungi with fissitunicate asci are a clade derived from them. Ascolocular lichens are polyphyletic, whereas ascohymenial lichens comprise a monophyletic group that includes the Lecanorales. Our data are not consistent with a derived origin of Eurotiomycetes including Aspergillus and Trichophyton from within a lichen-forming ancestral group. For these reasons, the results of this study are considerably at variance with the conclusion that major fungal lineages are derived from lichensymbiotic ancestors. Interpretation of our results in the context of early work suggests that ascoma ontogeny and centrum characters are not in conflict with the molecular data.

Morphology and ultrastructure of Neolecta species

Several independent molecular phylogenetic analyses have indicated that the genus Neolecta has a unique position within the Ascomycota. It is the only taxon outside the core-group of filamentous, ascoma-forming ascomycetes that also has the ability to form ascomata. Light and electron microscope studies indicate that hymenial structure and development in Neolecta spp. are unique. Ascogenous hyphae in N. vitellina branched repeatedly and successively to produce asci. Non-ascogenous hyphae were multinucleate, often with nuclei in pairs. Nuclear pairing was particularily prominent in the ascogenous hyphae. A basal septum delimited the dikaryotic ascus. Ascosporogenesis was initiated by nuclear fusion followed by a meiotic and mitotic division to form eight nuclei. The ascus apex was thin with an annular subapical thickening. Ascospores were forcibly released through a 'split' in the ascus apex. Woronin bodies were frequently associated with hyphal septa. Attempts to culture N. vitellina and to obtain molecular information from the type species, N. flarovirescens, were unsuccessful. However, N. flavovirescens showed several microscopic characters that indicated close relationships with the two other species in the genus, N. vitellina and N. irregularis. The position of Neolecta spp. within the Ascomycota is discussed.

Molecular systematics of the dimorphic ascomycete genus Taphrina

The ascomycete genus Taphrina Fries comprises nearly 100 species recognized by their mycelial states when parasitic on different vascular plants. Whereas the filamentous state is strictly phytoparasitic, the yeast state is saprobic and can be cultured on artificial media. Taphrina species are differentiated mainly on the basis of host range and geographical distribution, type and site of infection and morphology of the sexual stage in infected tissue. However, there has been little progress in the systematics of the genus in recent years, mainly because of the scarcity of molecular studies and available cultures. The main aim of the present study was the reappraisal of species boundaries in Taphrina based on the genetic characterization of cultures (yeast states) that represent about one-third of the currently recognized species. The molecular methods used were (i) PCR fingerprinting using single primers for microsatellite regions and (ii) determination of nucleotide sequences of two approx. 600 bp nuclear rDNA regions, the 5' end of the 26S rRNA gene (D1/D2 domains) and the internal transcribed spacer region (which includes the 5.8S rRNA gene). Sequencing results confirmed the monophyly of the genus (with the probable exclusion of Taphrina vestergrenii) and the combined analysis of the two methods corroborated, in most cases, separation of species defined on the basis of conventional criteria. However, genetic heterogeneity was found within some species and conspecificity was suggested for strains that have been deemed to represent distinct species. Sequences from the ITS region displayed a higher degree of divergence than those of the D1/D2 region between closely related species, but were relatively conserved within species (> 99% identity) and were thus more useful for the effective differentiation of Taphrina species. The results further allowed other topics to be addressed such as the correlation between the molecular phylogenetic clustering of certain species and the respective host plant family and the significance of molecular methods in the accurate diagnosis of the different diseases caused by Taphrina species.

Ribosomal DNA and resolution of branching order among the ascomycota: how many nucleotides are enough?

Molecular phylogenies for the fungi in the Ascomycota rely heavily on 18S rRNA gene sequences but this gene alone does not answer all questions about relationships. Particularly problematical are the relationships among the first ascomycetes to diverge, the Archiascomycetes, and the branching order among the basal filamentous ascomycetes, the Euascomycetes. Would more data resolve branching order? We used the jackknife and bootstrapping resampling approach that constitutes the "pattern of resolved nodes" method to address the relationship between number of variable sites in a DNA sequence alignment and support for taxonomic clusters. We graphed the effect of increasing sizes of subsamples of the 18S rRNA gene sequences on bootstrap support for nodes in the Ascomycota tree. Nodes responded differently to increasing data. Some nodes, those uniting the filamentous ascomycetes for example, would still have been well supported with only two thirds of the 18S rRNA gene. Other nodes, like the one uniting the Archiascomycetes as a monophyletic group, would require about double the number of variable sites available in the 18S gene for 95% neighbor-joining bootstrap support. Of the several groups emerging at the base of the filamentous ascomycetes, the Pezizales receive the most support as the first to diverge. Our analysis suggests that we would also need almost three times as much sequence data as that provided by the 18S gene to confirm the basal position for the Pezizales and more than seven times as much data to resolve the next group to diverge. If more data from other genes show the same pattern, the lack of resolution for the filamentous ascomycetes may indicate rapid radiation within this clade.

Genetic divergence at the SODA locus of six different formae speciales of Pneumocystis carinii

Genetic divergence at the SODA (manganese-dependent superoxide dismutase, MnSOD) locus were compared in six Pneumocystis carinii formae speciales isolated from mouse, rabbit, human, macaque and pig. A degenerate oligonucleotide primer strategy was designed to amplify 85-90% of the full-length SODA gene from P. carinii genomic DNA isolates. DNA sequence analysis revealed an A/T bias in the nucleotide composition (71-77.2%) and the presence of seven small introns (41-142 bp), interrupting each P. carinii open reading frame (ORF) at the same position. The MnSOD deduced amino acid sequences from all P. carinii isolates shared residues which were conserved within the MnSOD family and which are required for enzymatic activity and binding of the cofactor metal. Phylogenetic analysis including MnSOD sequences from representatives of the fungal phyla Basidiomycota and Ascomycota indicated that the P. carinii formae speciales form a monophyletic group that is related to the budding yeasts (subphylum Saccharomycotina, previously called class Hemiascomycetes) in the Ascomycota. In the whole Pneumocystis group, P. carinii f. sp. hominis, P. carinii f. sp. macacae and P. carinii f. sp. oryctolagi MnSOD sequences clustered together, as did the rat-derived P. carinii and P. carinii f. sp. muris sequences.

Isolation and characterization of alpha-tubulin genes from Septoria tritici and Rhynchosporium secalis, and comparative analysis of fungal alpha-tubulin sequences

The alpha-tubulin genes from Septoria tritici and Rhynchosporium secalis have been cloned and sequenced. The predicted amino acid sequence and intron structure showed strong homology with other known filamentous fungal alpha-tubulins. Comparison of sixteen fungal alpha-tubulin sequences based on amino acid sequence homology and intron structure identified five groups of proteins. Group 1 consists of filamentous fungi, including S. tritici and R. secalis, the dimorphic fungus Histoplasma capsulatum, and Pneumocystis carinii. Group 2 includes two divergent isoforms from Neurospora crassa and Aspergillus nidulans. Group 3 includes the yeast Saccharomyces cerevisiae and the dimorphic fungus Candida albicans. Group 4 contains the single yeast Schizosaccharomyces pombe. Group 5 includes the only Basidiomycete, Schizophyllum commune. This analysis supports the classification of P carinii as a primitive Ascomycete. The presence of an additional glycine residue between the second and third amino acid found only in Group 2 proteins may indicate a functionally distinct fungal isotype. Implications in terms of structure-function relationships for alpha-tubulin molecules are discussed.

Molecular taxonomy of yeasts

In the last two decades the application of molecular techniques has had a major impact on the classification of yeasts. The nuclear DNA relatedness has become the basis of species delineation. Molecular fingerprinting methods such as analysis of restriction fragment length polymorphisms, random amplified polymorphic DNA, PCR-amplified sequences and fragments, pulsed field gel electrophoresis of chromosome DNA and others allow intraspecies differentiation and typing. The most far reaching method has been the sequencing of various parts of ribosomal DNA that has made for the first time possible to assess the phylogenetic relationships among yeasts at different taxonomic levels. Based on the molecular data obtained so far several changes have been introduced in the classification of yeasts, however, substantial restructuring of current taxonomic schemes with the consequence of numerous nomenclatural changes must await further studies.

Identity of the xerophilic species Aspergillus penicillioides: Integrated analysis of the genotypic and phenotypic characters

We examined the identity of Aspergillus penicillioides, the typical xerophilic and strictly anamorphic species, using an integrated analysis of the genotypic and phenotypic characters. Our experimental methods on two genotypic characters, i.e., DNA base composition using the HPLC method and DNA relatedness using the nitrocellulose filter hybridization technique between A. flavus, A. oryzae, and their close relations revealed a good agreement with the values by buoyant density (for DNA base composition) and spectrophotometric determination (for DNA relatedness) reported by Kurtzman et al. in 1986. On the basis of these comparisons, we examined DNA base composition and DNA relatedness of six selected strains of A. penicillioides, including IFO 8155 (originally described as A. vitricola), one strain of A. restrictus, and the respective strains from Eurotium amstelodami, E. repens, and E. rubrum. As a result, five strains within A. penicillioides, including the neotype strain NRRL 4548, had G+C contents of 46 to 49 mol%, whereas IFO 8155 had 50 mol%. A. restrictus had 52 mol%, and three Eurotium species ranged from 46 to 49 mol%. The DNA relatedness between A. penicillioides (five strains), except for IFO 8155, exhibited values greater than 70%, but the DNA complementarity between four strains and IFO 8155 in A. penicillioides revealed values of less than 40%. DNA relatedness values between three species of Eurotium were 65 to 72%. We determined 18S, 5.8S, and ITS rDNA sequences as other genotypic characters from A. penicillioides (six strains), A. restrictus, and related teleomorphic species of Eurotium. In three phylogenetic trees inferred from these sequences, five strains of A. penicillioides, including the neotype strain, were closely related to each other, whereas IFO 8155 was distantly related and grouped with other xerophilic species. Our results have suggested that A. penicillioides typified by NRRL 4548 and A. penicillioides IFO 8155 (ex holotype of A. vitricola) are not conspecific. The enzyme patterns as a genotypic character and general morphology and conidial ornamentation types as phenotypic characters supported this conclusion. Therefore the name A. vitricola Ohtsuki, typified by the holotype strain IFO 8155, should be revived. Evolutionary affinities among Aspergillus species and related teleomorphs, including the xerophilic taxa, are discussed.

A molecular phylogenetic reappraisal of theGraphiumcomplex based on 18S rDNA sequences

Based on nuclear encoded small subunit (18S) rDNA sequences, a taxonomic reappraisal of Graphium (anamorphic fungi) was undertaken using neighbour-joining (NJ) and fast DNA maximum likelihood (fastDNAml) methods and compared with traditional classifications. In common with Graphium putredinis, Graphium penicillioides (the lectotype species) was found to be related to the Microascales, not the Ophiostomatales as previously believed. Both species might be heterogenous and should be treated as species aggregates. The representative mode of conidiogenesis for these two species was nodular-annellidic, rather than the dense-annellidic mode characteristic of the synnematous ophiostomatalean anamorphs. Graphium is emended to be restricted to G. penicillioides, G. putredinis, and related synnematous anamorphs of Petriella and Pseudallescheria, and a nomenclator for the nine species presently accepted in Graphium is presented. Pesotum, originally characterized mainly by sympodial conidiogenesis, is emended to include synnematous anamorphs of Ophiostoma species formerly included in a variety of genera with sympodial to dense-annellidic conidiogenesis. Eight new combinations in Pesotum are included in a nomenclator for the 26 species currently known. Three new combinations from Ceratocystis to Ophiostoma are proposed for species with Pesotum anamorphs. The holomorph of Graphium calicioides has affinities to the black yeasts and should be classified in the Chaetothyriales. However, the critical morphological, loculoascomycetous characters of the teleomorph are not completely documented. Interpreted from the molecular context, the morphological similarities between these three groups of anamorphs are homoplasies and examples of convergent evolution.Key words: Chaetothyriales, Graphium, Microascales, Ophiostomatales, Pesotum, 18S (SSU) rDNA sequences.

Multiple origins of fungal group I introns located in the same position of nuclear SSU rRNA gene

The archiascomycetous fungus Protomyces pachydermus has two group I introns within the nuclear small subunit (nSSU) rRNA gene. One of these introns has an internal open reading frame (ORF) that encodes a predicted protein of 228 amino acid residues. On the other hand, Protomyces macrosporus has two group I introns that insert at the same positions as P. pachydermus, which have no ORF. Each alignment was constructed with Protomyces group I introns located in the same position and other introns retrieved by the BLAST Search. Each phylogenetic tree based on the alignment shows that Protomyces introns are monophyletic but the relationships among fungal introns do not reflect on the fungal phylogeny. Therefore, it is suggested that two different horizontal transfers of group I introns occurred at the early stage of Protomyces species diversification.

Phytopathogenic filamentous (Ashbya, Eremothecium) and dimorphic fungi (Holleya, Nematospora) with needle-shaped ascospores as new members within the Saccharomycetaceae

Phylogenetic relationships between species from the genera Kluyveromyces and Saccharomyces and representatives of the Metschnikowiaceae (Holleya, Metschnikowia, Nematospora) including the two filamentous phytopathogenic fungi Ashbya gossypii and Eremothecium ashbyii were studied by comparing the monosaccharide pattern of purified cell walls, the ubiquinone system, the presence of dityrosine in ascospore walls, and nucleotide sequences of ribosomal DNA (complete 18S rDNA, ITS1 and ITS2 region). Based on sequence information from both ITS regions, the genera Ashbya, Eremothecium, Holleya and Nematospora are closely related and may be placed in a single genus as suggested by Kurtzman (1995; J Industr. Microbiol. 14, 523-530). In a phylogenetic tree derived from the ITS1 and ITS2 region as well as in a tree derived from the complete 18S rDNA gene, the genus Metschnikowia remains distinct. The molecular evidence from ribosomal sequences suggests that morphology and ornamentation of ascospores as well as mycelium formation and fermentation should not be used as differentiating characters in family delimitation. Our data on cell wall sugars, ubiquinone side chains, dityrosine, and ribosomal DNA sequences support the inclusion of plant pathogenic, predominantly filamentous genera like Ashbya and Eremothecium or dimorphic genera like Holleya and Nematospora with needle-shaped ascospores within the family Saccharomycetaceae. After comparison of sequences from the complete genes of the 18S rDNA the genus Kluyveromyces appears heterogeneous. The type species of the genus, K. polysporus is congeneric with the genus Saccharomyces. The data of Cai et al. (1996; Int. J. Syst. Bacteriol. 46, 542-549) and our own data suggest to conserve the genus Kluyveromyces for a clade containing K. marxianius, K. dobzhanskii, K. wickerhamii and K. aestuarii, which again can be included in the family Saccharomycetaceae. The phylogenetic age of the Metschnikowiaceae and Saccharomycetaceae will be discussed in the light of coevolution.

Mixia osmundae: transfer from the Ascomycota to the Basidiomycota based on evidence from molecules and morphology

To determine phylogenetic placement of Mixia osmundae (T. Nishida) Kramer (Mixiaceae, Protomycetales), we sequenced the nuclear small subunit ribosomal RNA (18S rRNA) gene from M. osmundae IFO-32408 and compared it with that from 4 archiascomycetes (Ascomycota) and 24 basidiomycetes. Our molecular phylogeny indicates that M. osmundae and the basidiomycetes Rhodosporidium toruloides, Leucosporidium scottii, Sporobolomyces roseus, Sporidiobolus johnsonii, Cronartium ribicola, Peridermium harknessii, and Erythrobasidium hasegawianum group together in 100% of bootstrap replicates. The M. osmundae spores on the host fern Osmunda japonica have been regarded as ascospores (i.e., endogenously produced within an ascus), but our light microscopic, SEM, and TEM observations for fresh materials of M. osmundae on O. japonica in Japan clearly demonstrated that these are produced exogenously, blastically, and simultaneously from the sporogenous cell. Evidence from both molecular and morphological characters suggests that M. osmundae is not a member of the ascomycetes and is not related to either the Taphrinales or Protomycetales. Obviously Mixia osmundae is a member of the basidiomycetes and placed within the simple septate basidiomycete lineage. Key words: fungal evolution, basidiomycete phylogeny, Mixia osmundae, Taphrinales, Protomycetales, 18S rRNA.