Book of Abstracts (PDF) - International Mycological Association

IMC7 Thursday August 15th Lectures
258 - Functional genomics in Candida albicans for drug
target discovery
R. Calderone
Georgetown University Medical Center, Department of
Microbiology & Immunology, Washington, DC, U.S.A.
Current anti-fungals used to treat human diseases are few
in number or invariably toxic. Most new anti-fungals are
chemically modified versions of existing compounds that
act against the same fungal targets [ergosterol synthesis, for
instance]. The complete sequence of the Candida albicans
genome has made it possible to utilize new strategies in
order to identify targets that can be exploited in drug
discovery. How does one select those genes [ORFs] that
are the most appropriate for target validation? Most of the
important ORFs are decided so by mostly 'common sense'
thinking, including, first, the target should be represented
in a number [if not all] of the human fungal pathogens but
not in the human genome, or, if present, there should be
sufficient differences that can be exploited. Secondly, the
target should be vital to the infection process. Third, the
function of the gene product should be at least partially
understood so that appropriate assays can be established.
Fourth, the gene product should be essential for growth or
viability of the fungus, although virulence factors that are
not essential for growth may be candidates. The spectrum
of a candidate target is limited in definition since, except
for the C. albicans genome, sequences for other human
pathogens are non-existent or incomplete. In this
symposium, topics related to the identification of
functional gene homologues, target identification and
validation will be presented.
259 - Carbon dioxide exchange, diffusion resistances
and water content in lichens: Laboratory and field
T.G.A. Green 1* & O.L. Lange 2
1 Waikato University, Hamilton, New Zealand. -
2 Universitaet Wuerzburg, Wuerzburg, Germany. - E-mail:
greentga@waikato.ac.nz
Jumelle in 1892, first commented on depressed net
photosynthesis at high thallus water contents and Stocker,
in 1927, the first to infer that it was due to diffusion
limitations. The topic attracted attention after
demonstrations of its occurrence by Kershaw in the 1970s.
There followed a period of contention as to what actually
caused the depression. Two possibilities were proposed,
depression through increased respiration or through
increased diffusion resistances for carbon dioxide.
Evidence, including chlorophyll fluorescence analysing
activity of the photosynthetic apparatus and helox for direct
determination of resistances, has consistently supported the
changed diffusion resistances theory. This evidence will be
summarised as well as field results that demonstrate the
ecological importance of the depression in carbon gain.
Although first found and described in the laboratory,
suprasaturation depression of NP is not an experimental
artefact but an important ecological feature of many lichen
species in many habitats. As an example, averaged over a
total year, net photosynthesis of Leconora muralis was
heavily reduced through suprasaturation during 38.5% of
the time when photosynthesis was possible. Despite these
confirmations of the role of diffusion resistances there is
still little agreement as to where these diffusion pathways
are actually located. An interpretation of the thallus will be
presented based on standard water potential water vapour
considerations.
260 - Hydrophobins in lichen-forming asco- and
basidiomycetes
R. Honegger 1* , S. Scherrer 2 & M.L. Trembley 3
1 University of Zürich, Institute of Plant Biology,
Zollikerstr. 107, CH-8008 Zürich, Switzerland. -
2 University of Minnesota, 100 Ecology Building, 1987
Upper Buford Circle, St. Paul, MN 55108, U.S.A. - 3 (no
institution), Gempenstrasse 18, CH-4053 Basel,
Switzerland. - E-mail: rohonegg@botinst.unizh.ch
Main building blocks of heteromerous lichen thalli are
hydrophilic, conglutinate pseudoparenchyma (peripheral
cortex) and loosely interwoven plectenchyma built up by
aerial hyphae with hydrophobic wall surfaces (medullary
and photobiont layers). Wall surface hydrophobicity
prevents the thalline interior from getting waterlogged at
high levels of hydration and facilitates gas exchange 1 . This
wall surface hydrophobicity was shown to be primarily due
to class 1 hydrophobins. Several hydrophobins were
biochemically and genetically characterised: one from the
haploid vegetative thallus of each of 4 Xanthoria spp.
(XPH1/parietina, XEH1/ectaneoides, XFH1/flammea,
XTH1/turbinata) 2, 4 and three from the dikaryotic,
lichenized basidiocarp of Dictyonema glabratum (DGH1,
DGH2, DGH3) 5 . With in situ hybridisation techniques
hydrophobin gene expression was located in medullary
hyphae of X. parietina 3 or in the photobiont layer, the
lower stratum and the boundary layer to the hydrophilic
tomentum in D. glabratum, respectively 6 . An antibody
raised against the recombinant DGH1 bound on ultrathin
sections to the electron dense outermost wall layer of
hyphae in the photobiont layer where rodlets had been
resolved in freeze-etch preparations 6 . 1 Honegger (2001)
THE MYCOTA IX: 165-188; 2 Scherrer et al. (2000)
FGBI 30:81-93; 3 Scherrer et al. (2002) New Phytol.
154:175-184; 4 Scherrer & Honegger, unpubl.; 5 Trembley
et al. (2002a) FGBI 35:247-259; 6 Trembley et al. (2002b)
New Phytol. 154:185-196.
Book of Abstracts 83