Growth, Differentiation and Sexuality

11 Autoregulatory Signals in Mycelial Fungi
U. Ugalde 1
CONTENTS
I. Introduction ......................... 203
II. Germination ......................... 204
III. Colony Morphogenesis ................. 205
IV. Asexual Development .................. 207
V. Sexual Development ................... 208
VI. Dimorphism ......................... 210
VII. Conclusions .......................... 210
References ........................... 211
I. Introduction
The mycelium is a very successful colony form capable
of orchestrating the development of different
cell types in response to the microenvironments
which it encounters. This attribute in particular
has led to the realisation that the mycelium
is governed by a sophisticated chemosensitive system.Manyoftheelementsofthissystemhaveprobably
been already inventoried after several decades
of intense research, but the functional connections
between them remain largely undiscovered. On
the one hand, many reported colony functions
have been ascribed to as yet unidentified chemical
signals, whilst on the other, many thousands of
molecules have been purified and characterised,
of which relatively few have been credited with
a biological role.
Those signals recognised so far comprise two
large categories. First, those directed at relations
with other organisms, such as hosts and including
elicitors and inhibitors, competitors involving antibiotics,
and predators where mycotoxins are implicated
(for further information, see The Mycota,
Vols. VA, X and XI).
The second category consists of in-house signals
which formerly fell under the generic term
1 Biochemistry Laboratory II, Faculty of Chemistry, University of
The Basque Country, P.O. Box 1072, 20080 Donostia-San Sebastian,
Spain
hormones (Gooday 1994), and are now separately
considered. They include pheromones, which facilitate
the interaction of compatible gametes, and developmental
hormones regulating the formation or
maintenance of differentiated multicellular structures
or protoorgans, such as ascomata or basidiomata.
These will not be dealt with in this chapter,
but individually in Chaps. 12 (Pheromone action in
the fungal groups Chytridiomycota, and Zygomycota,
and in the Oomycota), 17 (Mating type genes
of the basidiomycetes) and 16 (Fruiting body development
in ascomycetes) of this volume respectively.
In addition to these important in-house
signals, there is an array of endogenous cues
which convey information on environmental
conditions or the status of cells within the
mycelium, thus ensuring a coordinated colony
function. They are transmitted by extracellular
metabolites, and their signalling action results in
adaptations which are advantageous to the colony
as a living unit. In the past, these signals have
been referred to as autoinducers, autoinhibitors,
quorum sensing factors and morphogens. From
a functional viewpoint, they all share the feature
of regulating transitions between alternative
morphogenetic and/or functional programmes,
hence the proposal to term them collectively as
autoregulators. Signallingmoleculesperforming
equivalent tasks had already been assigned this
term when first discovered in filamentous bacteria
(Horinouchi and Beppu 1992). However, the range
of activities covered in mycelial fungi can be
presumed to be wider and more complex in light
of the information now available on secondary
metabolites and fungal development (Calvo et al.
2002).
This review will focus on those autoregulatory
signals which are involved in germination, colony
morphogenesis, and asexual and sexual development
in mycelial fungi. Finally, the incidence of
autoregulators in dimorphism will also be covered.
The Mycota I
Growth, Differentation and Sexuality
Kües/Fischer (Eds.)
© Springer-Verlag Berlin Heidelberg 2006