Handbook Part 2 - International Mycological Association

PS4-414-0400
Carbon and Nitrogen Dynamics of Mycena epipterygia Decomposing Pine Needles
J.B. Boberg, R.D. Finlay, J. Stenlid, B.D. Lindahl
Dept. of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden
Anthropogenic nitrogen inputs to many forest ecosystems have increased but their effects on litter decomposition are
not fully understood. It has for long been a dogma that decomposer systems are C-limited, since additions of labile
carbohydrates increases respiration. Many studies suggest that litter degrading microorganisms are often limited by
low N availability. However, additions of N have often been observed to have no or negative effects on
decomposition, particularly the decomposition rate of more recalcitrant material seen in a longer time perspective.
Underlying these contradicting results are methodological problems associated with field experiments with complex
microbial communities and food webs. Additions of labile C or N may lead to drastic changes in the microbial
community. The relationship between microbial growth and decomposition rates is also difficult to monitor in field
experiments. Detailed laboratory studies of decomposition under controlled conditions and with known decomposer
organisms may potentially shed light over the contradicting observations made from field conditions.
The aim of this study is to evaluate the potential of the litter decomposing fungus Mycena epipterygia to alter its C-
use efficiency (C biomass/C assimilated) in response to increased N and C availability. The fungus was grown
axenically on Scots pine needles and the effects of added glucose or ammonium on C-use efficiency were studied
by measuring the respiration and fungal biomass production over a 38 day period. Respiration was measured using
an Infra Red Gas Analyser (IRGA) and chitin analysis was used to estimate fungal biomass production.
Preliminary results indicate that N addition immediately increases respiration from pine needles in early stages of
decomposition. However, addition of glucose also increased respiration, but after a one week lag phase. The results
of the calculated C-use efficiency will be discussed in relation to the decomposition responses observed after N
addition.
PS4-415-0404
Selenium induces manganese peroxidase production by the white-rot fungus LSK-27
Tunc Catal, Candan Tamerler, Hakan Bermek
Istanbul Technical University, Department of Molecular Biology and Genetics, Istanbul, Turkey
Most white-rot fungi species secrete lignin-modifying enzymes such as manganese peroxidase (MnP), laccase, and
lignin peroxidase during their secondary metabolism which is generally triggered by nitrogen and/or carbon
deprivation. Various specific mechanisms for induction of enzyme production were previously reported in detail.
However, to our knowledge, the effects of selenium as an inducer for ligninolytic enzyme production in white-rot fungi
has never been studied. We demonstrated that selenium either induced or repressed MnP production in white-rot
fungus LSK-27, in a dose-dependent manner. While the higher concentrations of selenium repressed the MnP
production, lower selenium concentrations stimulated it by about 3 fold. Interestingly, smaller selenium concentrations
caused a decrease in the extracellular glutathione levels. These preliminary results indicate that selenium might
protect the organism from the oxidative stress, in a manner similar to that in higher eukaryotes.
PS4-416-0419
The H+-ATPase LmPMA1 is involved in pathogenicity of Leptosphaeria maculans on oilseed rape
E. REMY, M. MEYER, F. BLAISE, M. H. BALESDENT, T. ROUXEL
INRA-PMDV, Versailles, France
Leptosphaeria maculans, the causal agent of stem canker, is the major pathogen of oilseed rape all over the world.
In order to decipher the fungus infection strategies, and in parallel to the current genome initiative (see Balesdent et
al. communication), a collection of 3000 Agrobacterium-mediated transformants has recently been generated and
characterized in our laboratory. Here, we describe the phenotypic and functional characterization of one nonpathogenic
mutant, m210. M210 is morphologically similar to the wild type isolate in vitro and shows no growth or
sporulation defect. It induces a typical hypersensibility reaction on susceptible oilseed rape leaves and is totally
inefficient to colonize the stem. Formal genetic studies performed on a progeny of 54 isolates showed an exact cosegregation
between the m210 phenotype and the selection marker, thus confirming the efficient tagging of the
mutant. T-DNA border sequencing allowed us to localize its insertion within the promoter of one gene, 274 bp upstream
the start codon. The insertion results in the deletion of 7 bp of the promoter region. This gene is homologous to the
highly conserved fungal gene PMA1, which encodes the predominant and essential plasma membrane H+-ATPase.
The basic function of this protein in fungal cells is to create an electrochemical proton gradient, which drives the
uptake of nutrients by secondary active transport systems and regulates the intracellular pH. The Leptosphaeria
maculans H+-ATPase possesses all the characteristics common to other fungal H+-ATPases (conserved catalytic and
transmembrane domains). Quantitative RT-PCR analyses showed that LmPMA1 is expressed at a high level and in a
constitutive way in vitro (germinating conidia, mycelia) and in planta. In m210, the T-DNA insertion induced a 50%
reduced expression of LmPMA1 in in vitro growing mycelium but not in germinating conidia, compared to the wild
type. We suggest that the separation of transcriptional regulation boxes from the gene start by the T-DNA insertion led
to a deregulation of the expression in m210. In fungi, the expression of the H+-ATPase is under the control of
environmental pH and morphogenic development. We are actually investigating the influence of these two factors
on LmPMA1 expression, both in the wild type and mutant strains.
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