Growth, Differentiation and Sexuality

Fig. 14.2. A–E Different stages of conidiophore formation
in A. nidulans. InA, a stalk (S) swellsatthetipandforms
avesicle(V) from which several metulae (M) budoff(B).
The small buds enlarge fairly synchronously and form the
first mono-nucleate cell, the metula (C). In D, metulae produce
two to three phialides, which themselves generate the
long chains of conidia (C). Conidia are well prepared for
Fungal Asexual Sporulation 269
dispersion. The spore surface is covered with a rodlet layer
of hydrophobins (E). SEM images (A–C) wereextracted
from Fischer and Timberlake (1995). D was provided by R.
Weber (marburg), and the rodlets (E) werevisualizedby
atomic force microscopy by D. Veith (Karlsruhe). The scale
bar represents 10 μm in A–C, 100 μm in D, and 0.25 μm
in E
Fig. 14.3. Developmental mutant collection of A. nidulans (extracted from Fischer and Kües 2003)
a) Seven-Transmembrane
and Other Signal Receptors
Signals, such as pheromones, are perceived
at the cell surface, and thus they need to be
transduced into, and through the cytoplasm.
Seven-transmembrane receptors coupled to heterotrimeric
G-proteins are common signalling
modules for this process. In a systematic, reversegenetic
approach, the group of Yu identified nine
putative seven-transmembrane G-protein coupled
receptors(GPCR)inthegenomeofA. nidulans,and
subsequently generated loss-of-function mutations
for six of these (Han et al. 2004). Deletion of gprD
caused a severe reduction in vegetative growth and
asexual development, and a massive induction of
sexual development. Interestingly, environmental
conditions (e.g. high salt concentrations) which
repress sexual development, or mutations (e.g.
ΔnsdD) which inhibit sexual development restored
hyphal growth and asexual spore production. This
is a clear example that the three morphogenetic