Book of Abstracts (PDF) - International Mycological Association

IMC7 Tuesday August 13th Lectures
173 - Role of β-1,3-glucanase from Trichoderma
harzianum cect 2413 in antagonism against
phytopathogenic fungi
A.M. Rincón & T. Benítez *
Departamento de Genética, Facultad de Biología,
Universidad de SevillaUniversidad de Sevilla, Avenida
Reina Mercedes s/n, Spain. - E-mail: tahia@us.es
T. harzianum CECT 2413 grown under conditions of
simulated mycoparasitism secreted several β-1,3glucanases;
the most abundant, BGN13.1, was purified and
the corresponding gene, bgn13.1 was isolated. bgn13.1 is
strongly induced by chitin, autoclaved mycelia or plant
extracts and is only expressed at very narrow pH ranges
(around 5.5). There is a weak expression of the gene under
carbon starvation, and under some stress conditions. The
promoter sequence has putative boxes which respond to
stress, carbon (but not nitrogen) starvation, regulation by
pH and regulation under mycoparasitism (MYC). The
presence of MYC boxes in the promoter and the gene
induction by chitin strongly suggests that BGN13.1 is
involved in antagonism. BGN13.1 was overexpressed in T.
harzianum and tobacco plants. T. harzianum transformants
were more aggressive than the wild type in in vitro assays
against Botrytis, Phytophthora and Rhizoctonia but
maximal growth inhibition did not correlate with maximal
levels of β-1,3-glucanase activity. Combination of
BGN13.1 transformants with transformants which
overexpress other enzymes showed synergistic effects
against fungal strains, but the efficiency of both single
transformants or their mixture vary according to the
antagonized strain. Plant protection experiments with
different Rhizoctonia strains, T. harzianum and tobacco
plants, both wild types and BGN13.1 transformants are
currently in progress.
174 - Signaling cascades involved in the mycoparasitic
process by Trichoderma
A. Herrera-Estrella 1* , A. Mendoza-Mendoza 1 , V. Olmedo-
Monfil 1 , I. Chet 2 & B. Horwitz 3
1 Cinvestav, Km 9.6 libramiento Norte Carretera
Irapuato/León. AP 629. Irapuato, Gto., Mexico. - 2 The
Hebrew University of Jerusalem, P.O. Box 12, Rehovot
76100, Israel. - 3 Technion - Israel Institute of Technology,
Haifa 32000, Israel. - E-mail: aherrera@ira.cinvestav.mx
In the presence of a fungal host T. atroviride produces
hydrolytic enzymes and coils around the host hyphae. In a
biomimetic assay, different lectins induce coiling around
nylon fibers; coiling in the absence of lectins can be
induced by applying cAMP or the heterotrimeric G protein
activator mastoparan. We isolated a T. atroviride G alpha
subunit gene (tga1). Transgenic lines generated that
overexpress the Ga protein show very delayed sporulation
and coil at higher frequency. Furthermore, transgenic lines
that express an activated mutant protein with no GTPase
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Book of Abstracts
activity do not sporulate and coil at a higher frequency.
Lines that express an antisense version of the gene are
hypersporulating and coil at much lower frequency in the
biomimetic assay. Loss of Tga1 in these mutants correlates
with the loss of GTPase activity stimulated by the peptide
toxin mas-7. In contrast, cAMP levels and cAMPdependent
protein kinase activity drop when diffusible host
signals are encountered and the mycoparasitism related
genes ech42 and prb1 are highly expressed. Herewith we
show that the prb1 is subjected to Nitrogen Catabolic
Repression. Accordingly, induction of prb1 transcription
by Rhizoctonia solani cell walls requires the release from a
repressed condition, which is determined by nitrogen
availability. prb1 transcription in response to nitrogen
limitation, may be mediated by a MAPK signaling cascade.
175 - Components involved in regulation and signaling
of the mycoparasitic response of Trichoderma atroviride
S. Zeilinger 1 , C.K. Peterbauer 2 , K. Brunner 1 , V. Seidl 1 ,
R.L. Mach 1 & C.P. Kubicek 1*
1 Microbial Biochemistry and gene Technology Group,
Institute of Chemical Engineering, TU Wien,
Getreidemarkt 9/166 A-1060 Wien, Austria. - 2 Institute of
Biochemical Technology and Food Technology, University
of Agriculture, Muthgasse 11, A-1190 Wien, Austria. - Email:
ckubicek@mail.zserv.tuwien.ac.at
T. atroviride (former T. harzianum) strain P1 acts as a
mycoparasite and is applied as biological control agent
against a number of plant pathogenic fungi. The
mycoparasitic interaction is host-specific and not merely a
contact response. It is thus likely that signals from the host
are recognised and provoke antifungal activities which are
accompanied by morphological changes and the secretion
of hydrolytic enzymes. To understand the signalling
mechanisms involved in this process, we have begun to
investigate the cis- and trans-acting factors controlling
expression of the chitinases, using nag1 as a model because
its disruption leads to a complete loss of expression of all
chitinases. Three motifs were detected and characterized in
vivo and in vitro. A gene (seb1) encoding a protein binding
to one of these motifs (a CCCCT-box) was cloned from T.
atroviride and its biochemical and functional
characterization will be reported. Further, towards an
elucidation of the link between chitinase gene expression
and the mycoparasitic response, we have cloned key
components of the cAMP and MAP kinase signaling
pathways in T. atroviride and started their functional
characterization by gene disruption. First results from this
will be presented.