Book of Abstracts (PDF) - International Mycological Association

IMC7 Thursday August 15th Lectures
spores is demonstrated using both light microscopy and
transmission electron microscopy (TEM), and the process
of zoospore release is followed in a video sequence. A
phylogenetic tree (mitochondrial coxII gene) of
representative peronosporomycetes has been compiled
(Hudspeth & Hudspeth) and includes a few species of
nematode parasites.
252 - What makes a species? Redundancy,
recombination, and reproductive isolation
S.G. Oliver
School of Biological Sciences, University of Manchester,
2.205 Stopford Building, Oxford Road, Manchester M13
9PT, U.K. - E-mail: steve.oliver@man.ac.uk
The Saccharomyces "sensu stricto" group of yeast mate
with S. cerevisiae, but produce hybrids that yield spores of
very low viability, such that speciation seems to have
arisen via reproductive isolation. Chromosomal
rearrangements might act as a post-zygotic isolating
mechanism. We studied the distribution of chromosomal
translocations in 5 Saccharomyces "sensu stricto" species
(S. paradoxus, S. bayanus, S. cariocanus, S. mikatae and S.
kudriavzevii) by comparing them to the S. cerevisiae
genome. No correlation was found between the sequencedbased
phylogeny of these species and the presence of
translocations. Instead, bursts of rearrangements are seen
between closely related species, while more distant ones
have co-linear genomes. Thus, chromosomal
rearrangements are not the primary cause of yeast
speciation, but may intensify reproductive isolation once a
species has arisen by another route. We are using a novel
molecular approach to generate yeast strains containing
specific chromosomal translocations. Strains of S.
cerevisiae have been constructed that contain the
translocations found in other Saccharomyces "sensu
stricto" species. These are then mated, both to wild-type S.
cerevisiae and to the "sensu stricto" species whose genome
configuration they mimic. The data show that
translocations make a significant contribution to the postzygotic
isolation of species and indicate a mechanism for
genome duplication via allopolyploidy.
253 - Genus relationships in the Saccharomycetales
from multigene analyses
C.P. Kurtzman
National Center for Agricultural Utilization Research,
1815 N. University Street, Peoria, IL 61604, U.S.A. - Email:
kurtzman@ncaur.usda.gov
As with most fungi, circumscription of yeast genera is
based primarily on phenotype. Gene sequence
comparisons, such as from 18S or 26S rDNAs, have shown
that many presently defined yeast genera are not
monophyletic, but single gene analyses seldom provide
sufficient resolution to unambiguously circumscribe
genera. Analysis of the ca. 80 known species of the
Saccharomyces clade from EF-1, RNA polymerase II,
cytochrome oxidase II and actin, as well as from 18S, 26S
and mitochondrial small subunit rDNAs, individually gave
congruent terminal lineages and, when analyzed in
combination, provided strong genus-level support.
Intergeneric relationships are less well resolved making
family assignments uncertain. A comparison of species in
the phylogenetically distant Stephanoascus/Blastobotrys
clade gave similar results. Diagnostic phenotypes were
recognized for many of the phylogenetically defined
genera, but for some genera, there appeared to be no
unifying morphological or physiological characters.
254 - Molecular approaches to the re-appraisal of
species diversity within the ascomycete genus Taphrina
A. Fonseca * & M.G. Rodrigues
Centro de Recursos Microbiológicos (CREM), Secção
Autónoma de Biotecnologia, Faculdade de Ciências e
Tecnologia, Universidade Nova de Lisboa, Quinta da
Torre, 2829-516 Caparica, Portugal. - E-mail:
amrf@mail.fct.unl.pt
The dimorphic ascomycete genus Taphrina Fries
comprises nearly 100 species recognised by their mycelial
states parasitic on different vascular plants. Whereas the
filamentous state occurs exclusively in plant tissue, the
yeast state is saprobic and can be cultured on artificial
media. Taphrina species are differentiated mainly on the
basis of host range and geographic distribution, type and
site of infection, and morphology of the sexual stage in the
infected tissue. However, there has been little progress in
the systematics of the genus in recent years mainly due to
the scarcity of molecular studies and of available cultures.
Here we report on the molecular characterisation of
Taphrina spp. obtained from culture collections (yeast
states) in order to address the following topics: (i) is
Taphrina a well defined genus?; (ii) are species defined on
the basis of phenotypic criteria genetically distinct?; (iii)
does host specialisation underlie speciation in Taphrina?;
(iv) do Taphrina spp. occur naturally as saprobic yeast
forms?; (v) can molecular methods help in accurately
diagnosing the different diseases caused by Taphrina
species? The molecular methods used comprised PCRfingerprinting
using single primers for microsatellite
regions (MSP-PCR), and sequencing of two ca. 600 bp
long nuclear rDNA regions: the 5' end of the 26S rRNA
gene (D1/D2 domains) and the Internal Transcribed Spacer
(ITS) regions (including the 5.8S rRNA gene).
Book of Abstracts 81