Book of Abstracts (PDF) - International Mycological Association

IMC7 Wednesday August 14th Lectures
225 - Organization of genetic variation within
glomalean individuals
T.E. Pawlowska * & J.W. Taylor
University of California, Berkeley, CA 94720-3102, U.S.A.
- E-mail: tpawlows@nature.berkeley.edu
Understanding the organization of genetic variation within
individuals of arbuscular mycorrhizal fungi (Glomales) is a
prerequisite for the study of population genetics in this
group. Polymorphism of rDNA arrays within individual
glomalean spores inspired generally believed yet unproven
speculation that these fungi are largely heterokaryotic. We
tested this hypothesis using monoxenically cultured
Glomus etunicatum representing a natural population from
a maize field in California. In addition to the rDNA ITS1-
5.8S-ITS2 region, a putative gene encoding catalytic
subunit of DNA polymerase alpha (POL) was identified as
a variable genetic marker. To test for homo- vs.
heterokaryosis, we examined variant sorting of these two
markers in spores formed clonally in cultures initiated from
single spores. The markers were PCR-amplified from
individual spores, cloned and sequenced. In the initial
screen of the G. etunicatum experimental population, we
detected four variants of the rDNA ITS region and 16 POL
variants. We analyzed 16 to 200 clones per spore in 42
spores representing five single-spore cultures. The patterns
of the rDNA ITS and POL variant sorting in these cultures
were consistent with the homokaryotic model of nuclear
organization. The presence of distinct rDNA variants
within individual nuclei implies that concerted evolution,
which is responsible for homogenization of dispersed
rDNA arrays in genomes of other organisms, does not
operate efficiently in Glomales.
226 - Diversity and distribution of ericoid mycorrhizal
fungi in a Mediterranean forest
S. Perotto * , R. Bergero & M. Girlanda
Dipartimento Biologia vegetale dell'Univesità and IPP-
CNR, V.le Mattioli 25 -10125 Torino, Italy. - E-mail:
silvia.perotto@unito.it
Ericaeous plants are widespread on the globe and colonize
substrates ranging from humid mor-humus substrates to
arid sandy soils. This variety of habitats opens intriguing
questions on the biodiversity of their mycorrhizal
associates. Ericoid mycorrhiza (EM) has been regarded for
long time as a highly specific plant-fungus interaction,
featuring a very restricted number of fungal species. More
recent studies by research groups worldwide have
challenged this view as molecular analyses of EM fungi
suggest a greater genetic diversity and a larger number of
fungal species than previously thought. An interesting
feature of several EM fungi is the occurrence of Group I
introns in the small rDNA subunit, which further increases
their genetic diversity but which may also represent a
potential problem for RFLP analyses. The molecular
analysis of ericoid fungi has also lead to deeper
understanding of their ecology and relationships with
plants, and has revealed that ericaceous plants can be very
promiscuous, with multiple occupancy of their thin roots.
In addition, some EM fungi seem also able to colonise
plants from very distant taxa. We have studied EM fungusplant
relationships in Mediterranean forests, which are
complex environments where high biodiversity in plant
species and mycorrhizal types (arbuscular, orchid, ericoid,
ecto- and ectendo-mycorrhiza) occur. In these
environments, ectomycorrhizal and EM plants were found
to share similar root endophytes.
227 - Evolution of secondary metabolite pathways: nonribosomal
peptide synthetases and polyketide
synthetases
S. Kroken 1* , N.L. Glass 1 , J.W. Taylor 1 , B.G. Turgeon 2 &
O. Yoder 2
1 University of California at Berkeley, 111 Koshland Hall,
Berkeley, CA 94720-3102, U.S.A. - 2 Torrey Mesa Research
Institute, 3115 Merryfield Row, Suite 100, San Diego CA
92121-1125, U.S.A. - E-mail: kroken@nature.berkeley.edu
Our aim is to identify signaling factors (in pathways
required for hyphal network formation, sporulation,
vegetative growth and environmental sensing) present in
filamentous ascomycetes, and virulence factors necessary
for pathogenicity in plant pathogens. We hypothesize that
independent lineages recruited similar genes from their
non-pathogenic ancestors for novel roles in plant
pathogenesis. To test this hypothesis, we are performing
comparative genomics of saprobes (Neurospora crassa and
Aspergillus fumigatus) and plant pathogens (Cochliobolus
heterostrophus, Botrytis cinerea, Fusarium verticillioides
and F. graminearum). The first analyses identified genes
that encode polyketides (PKs) and non-ribosomal peptides
(NRPs). N. crassa has 7 polyketide synthases (PKSs) and 3
non-ribosomal peptide synthetase (NRPSs), whereas the
other filamentous ascomycete genomes have many more of
these genes. Phylogenies of PKSs and NRPSs each feature
a large clade that includes genes previously described as
virulence factors. However, N. crassa has six PKSs and
two NPRSs that group with the virulence clade, indicating
that these genes have other roles. Based on these
comparisons, we will select genes in N. crassa for
mutational analysis. In parallel with these mutational
analyses, metabolite profiling between wild-type N. crassa
and mutants will be performed to match PKS- and NRPSencoding
genes with secreted metabolites, which will be
characterized and tested for biological activities.
Book of Abstracts 73