Handbook Part 2 - International Mycological Association

0800-1000
PROFFERED SESSION 1 - Phylogeny 1
PS1PS1 - 0756
Demystifying Dothideomycetes – combining ultrastructure and molecular tools to study phylogenetic
relationships of fungi
UK Simon1, R Bauer1, D Begerow1, D Rioux 2, M Simard 2
1 Lehrstuhl Spezielle Botanik und Mykologie, Universität Tübingen, Tübingen, Germany, 2 Natural Resources Canada,
Canadian Forest Service – Quebec Region, Quebec, Canada
The Dothideomycetes (Ascomycota) is a major group of fungi that includes numerous phytopathogenous species and
some human and animal pathogens with an enormous variety of life-styles. Despite their economic and scientific
importance many taxonomic questions within this group remain unsolved at almost all taxonomic levels from
circumscription of orders to species delimitation. With the extraordinary interaction of Cymadothea trifolii, an
extracellular obligate biotrophic leaf pathogen, and its Trifolium host plants as a starting point we examine if the
combination of ultrastructural and molecular data can deepen our understanding of phylogenetic relationships within
the Dothideomycetes.
First, observations of the cellular interaction of high-pressure frozen and low-temperature embedded samples of C.
trifolii in Trifolium leaves are presented including results from immunocytochemical experiments with respect to
differential host cell wall degradation. These findings are compared with ultrastructural observations from other plantpathogen
interactions occurring in the Dothideomycetes. Finally, new nuSSU rDNA sequence data for C. trifolii are
integrated into phylogenetic analyses based upon a representative sampling of 120 Dothideomycetes.
C. trifolii obtains nutrients from its Trifolium hosts by means of a complex interaction structure. Remaining outside host
cells, the pathogen forms an intricate interaction apparatus in its own cells. Opposite this structure, the host
plasmalemma is triggered to produce a so-called bubble. In an extremely small area (ca. 400 nm wide) between
interaction apparatus and host bubble, the host cell wall is partially degraded: The pectin matrix is dissolved by fungal
enzymes, while cellulose and xyloglucan remain intact. Electron microscopic studies of other plant-pathogenic
Dothideomycetes have revealed a large variety of cellular interactions, but no structures resembling the one
produced by C. trifolii. NuSSU rDNA phylogenetic analyses show that C. trifolii clusters with the Mycosphaerella
punctiformis group.
The cellular interaction between C. trifolii and its Trifolium hosts is at present unique among the ascomycetes.
Furthermore, it is so far the only extracellular biotrophic fungus for which a highly localized differential host cell wall
degradation could be shown. Other fungi placed in the Dothideomycetes exhibit intracellular hyphae or haustorialike
structures. Subcuticulous or intercellular pathogens with no obvious interaction structures are also present. Previous
studies about the Exobasidiomycetes (Basidiomycota) have demonstrated that cellular interactions in plant
pathogenic fungi are a valuable tool for the reconstruction of phylogenetic relationships of such fungi, which has
been proven by molecular data. It is our objective to achieve the same for the Dothideomycetes. This should be a
point worthwhile to discuss with all scientists interested in the systematics of fungi.
PS1PS2 - 0453
The molecular phylogeny of the genus entoloma
DLV Co, ME Noordeloos
National Herbarium of the Netherlands, Leiden University, Leiden, Netherlands
Entoloma is a large genus characterised by pinkish, variously angular spores and large diversity in fruitbody
characteristics. Phylogenetic relationships in the genus Entoloma were investigated using sequence data from partial
sequences of three genes: RNA polymerase II second largest subunit (nRPB2), 28S ribosomal RNA (nLSU) and
mitochondrial small subunit ribosomal RNA genes(mtSSU). Sequenced were representatives of sections according to
Noordeloos’ classification of European Entoloma, species with ambiguous affinities, as well as new, yet unclassified
species. Results significantly support that nearly all Entoloma subgenera as currently delimited are not monophyletic,
with the possible exception of Pouzarella. Subgenus Entoloma forms a basal grade to the rest the genus except for
section Pseudonolanea, some of which proves to be truly part of subgenus Nolanea. Members of subgenus
Inocephalus are separated into six distinct clades, reflecting the heterogeneity allowed by the circumscription of this
subgenus. Subgenus Alboleptonia is separated into four clades, indicating that the character of pale fruiting bodies
has been over-emphasised. Despite the polyphyly of Entoloma subgenera, some clades still recognisably correspond
to subgenera Nolanea, Claudopus, as well as sections of the subgenera Leptonia, Entoloma and Inocephalus. This
study indicates the need for the re-evaluation of the infrageneric taxonomy of Entoloma and the characters used to
construct it.
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