Book of Abstracts (PDF) - International Mycological Association

IMC7 Wednesday August 14th Lectures
228 - Evolution of mating type genes in filamentous
ascomycetes
S. Poeggeler
Ruhr-Uni-Bochum, 44780 Bochum, Germany. - E-mail:
stefanie.poeggeler@ruhr-uni-bochum.de
To gain a deeper insight into the evolution of reproductive
life-cycles from filamentous ascomycetes, a comprehensive
sequence analysis of PCR-amplified sequences
corresponding to A- and a- specific mating-type sequences
was undertaken. The study included nine homothallic
(compatible) and eight heterothallic (incompatible)
members of the genera Neurospora and Sordaria. Distance
and parsimony trees based on gene fragments from the mat
a-1 and mat A-1 genes were compared with trees derived
from partial DNA sequences of the gpd glyceraldehyde-3phosphate
dehydrogenase gene. In contrast to the
sequences from the gpd gene, mating-type genes show
striking sequence differences suggesting that these genes
evolve very rapidly. Strong inter-relationships were found
among homothallic, as well as among heterothallic
members of both genera, indicating that in each genus, a
change from one reproductive strategy to another might
result from one single event. Pair-wise comparisons
between pheromone genes and pheromone receptor genes
of the heterothallic species Neurospora crassa and the
homothallic Sordaria macrospora revealed an extremely
low degree of nucleotide conservation in these genes,
indicating that these, like mating-type genes, evolved also
very rapidly.
229 - Phylogeny of Zygomycetes: multi-gene
approaches and the putative role of horizontal gene
transfer
K. Voigt
Friedrich Schiller Universitaet, Institute of Microbiology,
Department of General Microbiology and Microbial
Genetics, Fungal Reference Centre, Neugasse 24, D-07743
Jena, Germany. - E-mail: b5kevo@rz.uni-jena.de
The Zygomycetes encompass microscopic fungi which
form zygospores in sexual interactions. The most
prominent and largest order are the Mucorales comprising
saprotrophic and facultatively parasitic species, among
those, the soil fungi Chaetocladium brefeldii and
Parasitella parasitica which parasitize on other
mucoralean fungi during the establishment of plasma
bridges and the unidirectional transfer of genes to the host.
This parasexual interaction utilizes the pheromone trisporic
acid for the identification of compatible hosts, similarily to
sexual interactions. One of the last steps of trisporic acid
biosynthesis is catalysed by the 4-dihydromethyltrisporate
dehydrogenase. The gene encoding this aldo-keto reductase
were found in all families of the Mucorales, Mortierellales,
Entomophthorales and Kickxellales. The sequences were
analysed and used for the reconstruction of phylogenetic
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Book of Abstracts
trees. In order to study the evolution of Zygomycetes in
multi-gene approaches sequences for the nuclear-encoded
genes actin and beta-tubulin were also determined and
applied in concatenated analyses of tree constructions.
Phylogenetic analysis in the context of available sequence
data (approx. 6300 nucleotide positions per species)
revealed that current classification schemes for the
mucoralean fungi are highly unnatural at the family and, to
a large extent, at the genus level.
230 - RAPD and microsatellite analysis of the local and
global population structure of aflatoxigenic Aspergillus
species
N. Tran-Dinh 1 , J.I. Pitt 1 & D.A. Carter 2*
1 Food Science Australia, P.O. Box 52, North Ryde NSW
1670, Australia. - 2 School of Molecular and Microbial
Biosciences, University of Sydney, Maze Crescent,
Darlington, NSW 2006, Australia. - E-mail:
dee.carter@staff.usyd.edu.au
The mycotoxigenic species Aspergillus flavus and A.
parasiticus have been well characterised with regard
aflatoxin biosynthesis. Comparatively little is known,
however, on their natural population structure in the
environment. We have developed new molecular markers
based on RAPDs and microsatellites to analyse large
populations of these fungi on crops and in soils.
Investigation of an Australian field population revealed 1)
a new species of aflatoxigenic fungus, related but
genetically distinct from A. flavus was common in this
region. This is the same as the "Group 2" A. flavus,
previously reported by Geiser et al. (PNAS 94: 388-
393,1998); 2) recombination has occurred in the A. flavus
population, but the A. parasiticus population and the
population of the Group 2 A. flavus species are clonal; 3)
no clear distinction between toxigenic and nontoxigenic
strains in any of the species. Seven microsatellite markers
were then used to analyse a large, worldwide collection of
isolates. Globally, A. flavus was found to be cosmopolitan
and there was no geographic substructuring within this
species. In contrast, A. parasiticus was geographically
restricted, being very rare throughout all of Asia. Group 2
A. flavus isolates were likewise restricted, and all but two
came from the southern hemisphere. The microsatellite
data also indicated that genetic diversity was higher in A.
flavus than in either the Group 2 or the A. parasiticus
populations.