Book of Abstracts (PDF) - International Mycological Association

IMC7 Monday August 12th Lectures
fumigatus have shown that branching of the beta, 1-3
glucan through beta, 1-6 linkages is the first event in the
construction of the cell wall followed by linkages of the
branched glucan with chitin, galactomannan and beta 1-
3,1-4 glucan. In contrast to yeast, no proteins covalently
bound to cell wall polysaccharides that could play a
morphogenetic role in cell wall construction, have been
identified in A. fumigatus. Accordingly, branching enzymes
responsible for the linkages between polysaccharides
represent essential enzymes for the construction of the cell
wall. During the search of such glycosyltransferases, we
identified a beta 1-3 glucanosyltransferase playing an
important role in cell wall biogenesis. This enzyme that is
responsible for elongation of beta1-3 glucans, was
glycosylphosphatidyl inositol (GPI) anchored to the plasma
membrane. Comparative proteomic and genomic
approaches have identified 5 GPI-protein families common
to both A. fumigatus and yeast. None of the genes encoding
putative polysaccharide-bound proteins in yeast have been
found in A. fumigatus. Disruption of all the GPI-genes has
been undertaken in A. fumigatus. Up to now, data suggest
that the A. fumigatus GPI-proteins have enzymatic
functions involved in the biosynthesis of fungal cell wall.
30 - The regulation of chitin synthesis in yeast and
pathogenic fungi: A common theme?
C. Roncero * , M. Sanz, C. Jimenez, F. Castrejon & A.
Duran
CSIC/UNIVERSIDAD DE SALAMANCA, Avda. Campo
Charro s/n. 37007-Salamanca, Spain. - E-mail:
crm@usal.es
Chitin synthesis is a process maintained across the fungal
kingdom that, thanks to the power of genetic manipulation
of yeast cells, is now beginning to be understood. Chitin
synthesis is based on the regulation of distinct Chitin
Synthases (CS) isoenzymes, whose number ranges from 1
in Schizosaccharomyces pombe to 7 in some filamentous
fungi such as Aspergillus fumigatus. This high diversity
makes it difficult to find a unique model of regulation.
Sequence analysis, together with the functional data
reported, strongly support the notion that all fungi contains
two highly divergent CS families, one of each crucial for
cell division and the other involved in bulk chitin synthesis.
The first family is likely to be controlled at cell cycle level,
whereas the second one would depend on the function of
several genes whose function has been studied in the yeast
Saccharomyces. We review the current knowledge about
the function of such genes and whether these genes may be
conserved in other fungi. Finally, we discuss our recent
results in the characterization of some of these genes in A.
fumigatus and C. albicans.
12
Book of Abstracts
31 - Alpha and beta (1-3) glucan synthesis in Aspergillus
fumigatus
A. Beauvais * , W. Morelle, M. Diaquin & J.P. Latgé
Unité des Aspergillus, Institut Pasteur, Paris, France. - Email:
abeauvai@pasteur.fr
Alpha and beta (1-3)glucan are the main components of the
cell wall of A. fumigatus. Like in other fungi, beta (1-
3)glucan synthesis in A. fumigatus is under the control of
FKS and RHO1 that are essential genes. Two genes AGS1
and AGS2 encoding two putative alpha (1-3)glucan
synthases have been now characterized in A. fumigatus.
The predicted Ags1 and Ags2 proteins have an estimated
molecular size of 273 kDa. Ags1p and Ags2p have three
major hydrophobic regions separating two hydrophilic
domains. The first hydrophilic domain is homologous to
bacterial alpha amylases, and the second to bacterial
glycogen synthases. AGS1 and AGS2 were disrupted in A.
fumigatus. The ags1 and ags2 mutants have similar
phenotype. Growth and conidiation are both reduced.
Morphologically, abnormal sporulating structures were
seen in liquid culture during early growth, whereas the wild
type strain (WT) only produces mycelium. The ags1
mutant is more sensitive to the cell wall inhibitors
Nikkomycin and Congo Red than the WT and ags2 strains.
No difference was seen in the carbohydrate composition of
the alkali insoluble and soluble fractions of the cell wall of
ags2 and WT strains. In contrast, a reduction in the alpha
(1-3)glucan content of the alkali soluble fraction of the
ags1 was observed. These results were in agreement with
the immunolocalization of Ags1p and Ags2p since Ags1p
was localized at the cell wall whereas Ags2p was found in
the Golgi apparatus.
32 - Beta-Glucan synthesis in S. cerevisiae: a genomewide
synthetic lethal analysis of participating gene
families
G. Lesage, H. Li, A.-M. Sdicu, P. Menard & H. Bussey *
Department of Biology, McGill University, 1205 Avenue
Docteur Penfield, Montreal, Quebec H3A 1B1, Canada.
We used the yeast deletion set to find synthetic lethal and
sick interactions of genes involved in beta-glucan
synthesis, to define networks of participating genes. We
used deletion mutant arrays (Tong et al., 2001, Science
294: 2364) to make double mutants in query glucan genes.
We examined two gene families: FKS1, GSC2, FKS3 and
KRE6 and SKN1. For FKS1, encoding a beta-1,3-glucan
synthase, we find synthetic interactions with 82 genes,
principally in areas of wall maintenance, cell stress, protein
degradation, lipid and fatty acid metabolism and
transcription. For GSC2 and FKS3, we find 20 and 83
interactions respectively. Surprisingly, there is little
overlap between the sets for the three FKS genes, a total of
175 interactions involving 165 genes, reflecting the distinct
biological contexts in which these related proteins function.