Book of Abstracts (PDF) - International Mycological Association

IMC7 Tuesday August 13th Lectures
127 - Dissecting carbon metabolism in AM fungi:
Implications for symbiosis and biotrophy
B. Bago 1* , P.E. Pfeffer 2 , P. Lammers 3 & Y. Shachar-Hill 3
1 CSIC, CIDE, Cami de la Marjal s/n, Albal (Valencia),
Spain. - 2 USDA, ERRC, 600 E. Mermaid Ln. 19038
Wyndmoor, PA, U.S.A. - 3 NMSU, Dept. Chemistry and
Biochemistry, NMSU, 88033 Las Cruces NM, U.S.A. - Email:
berta.bago@uv.es
The obligate biotrophic nature of arbuscular mycorrhizal
fungi (AMF) has long been known but never overcome,
making all efforts of culturing these organisms
continuously under axenic conditions unsuccessful. This
has considerably limited progress in basic research and
biotechnological strategies for the large scale production of
AM fungal inoculum. All cytochemical, biochemical,
metabolic and genome investigations carried out the last 25
years indicated that AMF resemble saprophytes (e.g.
genome size, metabolic capabilities, capacities for DNA,
RNA and protein synthesis, etc.), however we are still
unable to make these fungi complete their life cycle in the
absence of a suitable host plant. One of the reasons
proposed for this failure is the existence of a metabolic lack
in their C metabolism. However, neither assays of involved
enzymatic activities revealed the origin of such a metabolic
blockage, nor did any of the numerous C sources assayed
in synthetic media induce the fungus to fulfil its life cycle
axenically. In recent years the application of a range of
experimental techniques including AM monoxenic
cultures, molecular biological methods, NMR spectroscopy
and in vivo microscopy has greatly contributed to our
understanding of C metabolism in AMF, both under
asymbiotic and symbiotic conditions. The results have shed
some light in the difficult, but fascinating question of the
obligate biotrophic nature of AM fungi.
128 - Carbohydrate and nitrogen dependent generegulation
in the ectomycorrhizal fungus Amanita
muscaria
U. Nehls * , A. Bock, R. Kleber & R. Hampp
Universitaet Tuebingen/Physiologische Ökologie der
Pflanzen, Auf der Morgenstelle 1/72076 Tuebingen,
Germany. - E-mail: uwe.nehls@uni-tuebingen.de
Carbohydrate and nitrogen support has a profound impact
on gene regulation and fungal physiology in saprophytic
ascomycetes. As saprophytic fungi, ectomycorrhizal fungi
live in environments with a different carbohydrate and
nitrogen support (e.g. extramatrical hyphae versus
mycorrhizal hyphae). To understand ectomycorrhizal
fungal physiology in soil and the symbiotic structure, the
effect of carbohydrate and nitrogen nutrition on fungal
gene expression is of special interrest. Northern blot
analysis was carried out for selected genes of the
ectomycorrhizal fungus A. muscaria. The fungus was
grown in liquid culture at different carbohydrate and
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Book of Abstracts
nitrogen conditions as well as in ectomycorrhizas. Genes
investigated so far encode a monosaccharide transporter, a
phenylalanine ammonium lyase, an excreted protease and
an amino acid transporter. These studies revealed an
interconnection between carbohydrate and nitrogen
dependent regulation of gene expression in A. muscaria
sharing homologies but also some differences to
ascomycetes. Ectomycorrhizal hyphae are not uniform but
consists of two 'fungal networks', the Hartig net that is
attached to root cortical cells (forming together the
plant/fungus interface), and hyphae that are ensheating the
infected root. Since both structures have different functions
with regard to carbohydrate and nitrogen uptake, storage
and partitioning, we also compared the expression of
fungal genes in both hyphal networks.
129 - Functional genomics of fungal-plant
communication in the arbuscular mycorrhizal
symbiosis
V. Gianinazzi-Pearson 1* , L. Brechenmacher 1 , M.
Tamasloukht 2 , D. van Tuinen 1 , G. Bécard 3 , S. LaCamera 1 ,
S. Gianinazzi 1 & P. Franken 2
1 UMR 1088 INRA/Université Bourgogne BBCE-IPM,
INRA-CMSE, BP 86510, 21065 Dijon Cedex, France. -
2 Max-Planck-Institut for Terrestrial Microbiology, Karlvon-Frisch-Strasse,
35043 Marburg, Germany. - 3 Equipe
de Mycologie Végétale, UMR 5546 CNRS/Université Paul
Sabatier, BP17, 31326 Castanet-Tolosan, France.
Fossil data indicate that arbuscular mycorrhizal (AM) fungi
already colonized early land plants so that AM formation
probably belongs to one of the earliest developmental
programs plants evolved. At the same time, rRNA
sequence analysis has shown that AM fungi form a
monophyletic group (Glomeromycota) of which little is
known about the biology of the possible progenitor.
Analyses of the symbiotic programme in AM interactions
have targeted fungal genes involved in cell wall synthesis,
nutrient metabolism or membrane transport, and plant
genes associated mainly with interactions with pathogenic
organisms or symbiotic rhizobia. Several non-targeted
approaches have also been used to further identify genes
involved in AM formation and/or function but very limited
information has been gained so far about fungal gene
expression. This has prompted us to adopt alternative
strategies of transcriptome analysis in a more extensive
search for genes involved in different stages of AM
development, based on suppressive subtractive
hybridisation and large scale cDNA sequencing.
Expression profiling has identified ESTs which correspond
to fungal genes that are induced by host root exudates in
pre-symbiotic phases or in mycelium during symbiotic root
interactions. Such global approaches of functional
genomics of AM will contribute to a better molecular
understanding of fungal-plant communication in these
widespread symbiotic associations and of how they
promote plant vigour.