Book of Abstracts (PDF) - International Mycological Association

IMC7 Friday August 16th Lectures
443 - Investigating the propagation pathway of
endobacteria in Gigaspora margarita
V. Bianciotto 1* , A. Genre 1 , P. Jargeat 2 , G. Bécard 2 & P.
Bonfante 1
1 Istituto Protezione Piante - Sezione di Torino CNR and
Dipartimento di Biologia Vegetale Universita' di Torino,
Viale Mattioli 25 -10125 Torino, Italy. - 2 UMR 5546
CNRS/Université Paul Sabatier Pôle de Biotechnologie
Végétale, 24, chemin de Borde-Rouge BP 17 Auzeville
31326, Castanet-Tolosan, France. - E-mail:
v.bianciotto@csmt.to.cnr.it
Intracellular bacteria live in the cytoplasm of many isolates
of arbuscular mycorrhizal fungi belonging to
Gigasporaceae. On the basis of 16S rDNA analysis these
endobacteria were assigned to a new taxon closely related
to the genera Ralstonia, Pandorea and Burkholderia. To
understand their propagation pathways through the life
cycle of Gigaspora margarita (BEG 34 isolate), in vitro
mycorrhizal cultures of transformed roots were produced.
The presence of bacteria in spores from filial generations
have been monitored by using confocal microscopy
observations together with molecular analysis. We
demonstrate for the first time the vertical transmission of
endobacteria from a single 'parental' spore (F0) to filial
spores through germinating and symbiotic mycelia. A
quantification of the endobacteria population was carried
out using 3D volume reconstruction. To verify whether the
presence of the whole plant could determine differences in
the transmission of bacteria, a F1 generation of spores was
produced on clover pots. In contrast with the in vitro
conditions, all the F1 spores from monosporal inocula were
free of bacteria, suggesting that bacterial migration is
controlled by multiple factors. Endobacterial activity was
investigated by using Acridine Orange. The bacterial
distribution pattern and activity, closely related to the
fungal life cycle, reinforces the hypothesis of a strong
symbiotic association between the two organisms.
Research supported by the EU Project GENOMYCA.
444 - Molecular bases of appressorium formation in
AM fungi
N. Requena * , E. Serrano & M. Breuninger
Botanical Institute, University of Tübingen, Auf der
Morgenstelle 1, 72076 Tübingen, Germany. - E-mail:
natalia.requena@uni-tuebingen.de
The appressorium development is the first morphogenetic
change which precedes the formation of the symbiotic
association between arbuscular mycorrhizal (AM) fungi
and their host roots. This event takes place after
recognition of yet unknown plant signals which trigger the
developmental decision of abandoning the so-called
asymbiotic life stage. Upon recognition of those signals the
fungus changes its straight pattern of hyphal tip growth to
form a swollen structure that hooks over a rhizodermis cell
and later develops the penetration peg among two adjacent
epidermal cells. The physical contact with the host root is
essential for the appressorium development. To investigate
the molecular bases for this morphogenesis we took a
comparative molecular approach and studied the changes
on gene expression that occurred to the fungus upon
induction with a host root. We induced appressorium
development on water agar medium by bringing into
contact parsley seedlings with germinated spores or
sporocarps of AM fungi. A time course of appressorium
development showed that first induction takes place around
120 h, while at 168 h a plateau in the number of
appressoria is achieved. We investigated both, early gene
expression and later gene expression in order to selectively
search for genes involved in signaling and recognition or
for genes responsible for structural changes. Results
concerning our progress in this topic will be presented.
445 - Extensive tubular vacuoles in arbuscular
mycorrhizal fungi
Y. Uetake * & M. Saito
Natl. Inst. Livestock Grassland Sci., Nishinasuno, Tochigi,
329-2793, Japan. - E-mail: yuetake@uoguelph.ca
Hyphae of Gigaspora margarita were stained with Oregon
Green 488 carboxy-DFFDA that is known to accumulate in
the lumen of fungal vacuoles, and were observed by laser
scanning confocal microscopy. Germ tubes had vacuoles
with one of the following types: A, longitudinally oriented
bundles of long tubules; B, both tubular and various sizes
of spherical vacuoles in various proportions; C, a mass of
spherical vacuoles. Stained germ tubes with cytoplasmic
streaming always showed A or B types of vacuoles, but
never C type. Tubular vacuoles were extremely fragile
when exposed to laser irradiation; many small spheres were
formed. Bundles of tubular vacuoles were also observed in
extraradical hyphae and intercellular hyphae of G.
margarita from co-cultures with onion seedlings. Tubular
vacuoles were observed also in the germ tubes of G. rosea,
Glomus leptotichum, Gl. intraradices, Scutellospora
cerradensis and in hyphae of other members of
Zygomycota, Rhizopus stolonier, Absidia repens, Mucor
meguroence, Choanephora infundibulifera, Mortierella
chlamydospora, Syncephalastrum racemosum, Linderia
bicolumnata. These results suggest that tubular vacuoles
are universal in Zygomycota. Ultrastructure of rapid
freeze-freeze substituted germ tubes of G. margarita
showed longitudinally oriented profiles of vacuoles
occupying most of the cell volume.
Book of Abstracts 137