Book of Abstracts (PDF) - International Mycological Association

IMC7 Tuesday August 13th Lectures
196 - Examining the relationship between nonself
recognition, heterokaryon incompatibility and hyphal
fusion in Neurospora crassa
N.L. Glass 1* , Q. Xiang 1 , S. Sarkar 1 , D.J. Jacobson 1 & N.D.
Read 2
1 Plant and Microbial Biology Department, University of
California, Berkeley, CA, 94720-3102, U.S.A. - 2 Institute of
Cell and Molecular Biology, University of Edinburg,
Edinburgh, EH9 EJH, U.K. - E-mail:
Lglass@uclink.berkeley.edu
Filamentous fungi grow by tip extension, branching and
hyphal fusion to form a hyphal network. Filamentous fungi
can also undergo hyphal fusion between individuals to
make vegetative heterokaryons. Recognition of nonself in
such heterokaryons is mediated by genetic differences at
het loci. Heterokaryons or transformants that contain
alternative het alleles show severe growth inhibition,
conidiation suppression and death. We use Neurospora
crassa to study the molecular mechanism of hyphal fusion
and the consequences of fusion between het incompatible
individuals. Live cell imaging of hyphal anastomoses
showed a self-signaling phenomenon which initiates the
multi-stage process of fusion. We identified four mutants
that fail to undergo hyphal fusion. Two mutations are in
genes encoding signal transduction components; these
mutants also suppress heterokaryon incompatibility
mediated by the mat locus. Nonself recognition during
heterokaryon incompatibility has been shown to be
mediated by the formation of a HET heterocomplex.
Suppressor analyses identified two additional loci that are
required for mediating heterokaryon incompatibility. One
of these mutants suppresses heterokaryon incompatibility
at both the mat and het-c locus. By these analyses, we hope
to shed light on nonself recognition mechanisms in
filamentous fungi that underlie heterokaryon
incompatibility and explore its relationship to the hyphal
fusion process.
197 - Somatic incompatibility in basidiomycetes.
Genetic analysis in Heterobasidion
J. Stenlid * , Å. Olson, N. Högberg & M. Lind
Dept Forest Mycology and Pathology, Swedish University
of Agricultural Sciences, Box 7026, S-750 07 Uppsala,
Sweden. - E-mail: Jan.stenlid@mykopat.slu.se
In basidiomycetes, intraspecific recognition of self and
non-self is mediated through the somatic incompatibility
(SI) system (similar to the vegetative compatibility system
in ascomycetes). It is expressed in the vegetative phase of
growth both in homokaryons and in heterokaryons when
dissimilar genotypes meet. In the homokaryotic stage, the
system can be overridden by mating. SI involves postfusion
cell death, and depending on the species involved,
activation of phenol oxidases, melanin production,
formation of clear zones of collapsed aerial hyphae, hyphal
knot cells or dense so called barrages. The genetic control
of SI has been studied in less than ten species. In members
of the genus Phellinus, SI was under control of one major
gene, while 3-4 genetic loci have been implied in
Heterobasidion, Collybia and Pleurotus. In this
presentation we describe a QTL approach to characterise
the genetic and molecular background to SI in
Heterobasidion annosum. A genetic map was constructed
using AFLP markers for a cross between a S and a P
homokaryon of H. annosum. Siblings were mated with the
parent mycelia and resulting heterokaryons, differing in
one sib-related nucleus, were paired in all combinations.
Putative loci for SI were mapped based on the
incompatibility reactions. Implications for future work will
be discussed.
198 - Overview of fungal lignin degradation
C.A. Reddy
Dept. of Microbiology & Molecular Genetics, Michigan
State University, East Lansing, MI 48824-4320, U.S.A. - Email:
reddy@msu.edu
Lignocellulose, a major component of woody biomass, is
the most abundant renewable organic material in the
biosphere and has important applications as a resource for
producing pulp and paper, animal feeds, and industrial
chemicals. Lignin, which limits access of microbial
enzymes to cellulose and hemicellulose in woody
materials, is a key limiting factor not only in the efficient
conversion of the latter to useful materials but also in
global carbon cycling. White-rot basidiomycetes are
efficient lignin degraders in natures and produce one or
more of three major classes of lignin-modifying enzymes
(LMEs) designated: laccases, lignin peroxidases (LiPs),
and manganese peroxidases (MnPs). LMEs are
extracellular, non-specific, metalloenzymes and catalyze
radical-mediated oxidative degradation reactions.
Cumulative evidence indicates that a large number of
isoenzymes of LiPs, MnPs, and laccases are produced by
various ligninolytic fungi and that different isoenzymes
appear to be encoded by individual genes which are
distributed on multiple chromosomes. Regulation of
production of LMEs appears to be subject to complex
interplay of nutritional, environmental, temporal, and
genetic factors. An overview of the studies on the
physiology and molecular biology of LMEs as well as
applications of ligninolytic fungi for bioremediation of
priority environmental pollutants will be presented.
Book of Abstracts 63