Book of Abstracts (PDF) - International Mycological Association

IMC7 Tuesday August 13th Lectures
124 - Fungi and lichen: microbial ecology in Antarctic
rock desert
C. Ascaso 1* , A. de los Rios 1 & J. Wierzchos 2
1 Centro de Ciencias Medioambientales, CSIC, Madrid,
Spain. - 2 Servei de Microscòpia Electrònica, Universitat de
Lleida, Spain.
Fungi and prolichens account for a substantial proportion
of the endolithic biomass of rock. To explore the
development and survival of epilithic and endolithic fungi,
visualisation technologies have to be stretched to their full
potential. These techniques have enabled the observation of
biologically transformed minerals in rocks from Antarctica,
including diagenetic iron hydroxide nanocrystals and clays
around chasmoendolithic fungi in sandstone, and calcium
oxalate and silica deposits close to fungal cells in granite.
As for any ecosystem, the study of the rock microhabitat,
requires previous knowledge of the components and the
processes that take place within it. The structure and
function of each component of the lithic microecosystem
needs to be established by quantifying and identifying the
fungi present in each lithobiontic niche and defining the
mineralogical features of these hidden microhabitats. Once
we have selected the techniques to observe these
components in situ and locate the presence of water, the
questions that need to be addressed are: how are the fungi
organised in the fissures and cavities, which fungi are
present and how many are there, what water relationships
are there and what effects do fungi have on the substrate's
minerals? This last question is crucial, since mechanical
and chemical changes in minerals and mineralisation of
fungal cells can lead to physical and/or chemical traces
(biomarkers), even after the death of the microorganism.
125 - Exploring the transcriptome of the
ectomycorrhizal symbiosis
F. Martin * , S. Duplessis, A. Kohler & D. Tagu
UMR IaM, Centre INRA de Nancy, 54280 Champenoux,
France. - E-mail: fmartin@nancy.inra.fr
Studies of the ectomycorrhizal symbiosis have highlighted
the role of transcriptional regulation in controlling the
morphological stages of symbiosis differentiation. To
examine gene-activity changes associated with the
development of the ectomycorrhizal symbiosis, we have
performed expression profiling using poplar, eucalypt and
Pisolithus cDNA arrays. A marked change in the gene
expression in the mycobiont and the host-plants was
observed at multiple levels: (a) a general activation of the
protein synthesis machinery probably supporting an intense
cell division/proliferation, (b) an increased accumulation of
transcripts coding for cell wall proteins in hyphae and roots
probably involved in the symbiotic interface formation, and
(c) the upregulation of energy metabolism in colonised
roots. This data suggests a highly dynamic environment in
which symbionts are sending and receiving signals, are
exposed to high levels of stress conditions and are
remodeling their tissues. With multiple EST/cDNA array
programmes dealing with ectomycorrhizal associations, we
will have in a near future an unparalleled opportunity to
ask which genetic features are responsible for
common/divergent traits involved in this symbiosis. A few
of the many possible breakthroughts will be in
characterisation of common transcriptional and
transduction networks and new insights into unique
metabolic routes critical for mycorrhiza functioning.
126 - Responses of mycorrhizal fungi to heavy metals: a
cellular and molecular investigation
L. Lanfranco 1* & P. Bonfante 2
1 Dipartimento di Biologia Vegetale Università di Torino,
Viale Mattioli 25, 10125 Torino, Italy. - 2 Istituto per la
Protezione delle Piante, Sezione di Torino, CNR, Viale
Mattioli 25, 10125 Torino, Italy. - E-mail:
luisa.lanfranco@unito.it
Within the fungal kingdom mycorrhizal fungi represent
direct links between plants and soil and are often needed to
ensure plant survival in heavy metals polluted areas. A
sterile mycelium PSIV, an ascomycete establishing ericoid
mycorrhiza, was used to understand how zinc ions affect
the cellular mechanisms of fungal growth. Chitin, the most
characteristic shape-determinant of fungal wall, was
quantified and located by specific probes. Conspicuous
changes in hyphal morphology were observed in zinctreated
mycelium, where hyphal walls were thicker and
chitin labelling was more intense. Chitin synthase genes
belonging to two classes were differentially expressed.
Morever, molecular mechanisms leading to protection
against heavy metals were investigated in an arbuscular
mycorrhizal fungus (Gigaspora margarita BEG34) and led
to evidence of a structurally novel metallothionein. The
gene, designated GmarMT1, encodes a functional
polypeptide capable of conferring increased tolerance
against cadmium and copper as revealed by
complementation assays in yeast. The GmarMT1 RNA is
expressed in both presymbiotic spores and symbiotic
mycelia even in the absence of metal exposure, but it is
significantly less abundant in the latter stage. An opposite
pattern was observed upon copper exposure, which
upregulated GmarMT1 expression in symbiotic mycelia,
but not in germinated spores. Part of this work is supported
by the European Project GENOMYCA (QLK5-CT-2000-
01319).
Book of Abstracts 41