Growth, Differentiation and Sexuality

Table. 1.1. (continued)
Generating Fungal Cell Types 9
Protein type Protein Organism Role Reference
Wal1p C. albicans Bud site selection, actin polarisation, Walther and
endocytosis and hyphal formation Wendland (2004b)
Ras GTPase Ras2p S. cerevisiae Required for activation of both the cAMP Toda et al. (1985);
and MAPK cascades which initiate
pseudohyphal growth
Gimeno et al. (1992)
Ras1p C. albicans Required for activation of both
the cAMP and MAPK cascades
which initiate filamentous growth
Leberer et al. (2001)
RasA A. nidulans Initiation of polarised growth
Som and
during conidial germination.
Kolparthi (1994);
Onset of asexual development
Osherov and May (2000)
RasA P. marneffei Initiation of polarised growth
during conidial germination.
Maintenance of polarised growth
of hyphae. Onset of asexual development.
Polarised growth of yeast cells
Boyce et al. (2005)
Ras1 C. trifolii Required for polarisation of hyphae,
sporulation and appressoria formation
Memmot et al. (2002)
MAPKKK, Ste11p, S. cerevisiae Required for pseudohyphal differentiation Reviewed in
MAPKK, Ste7p,
Lengeler et al. (2000)
MAPK Kss1p
Hst11,
Hst7p,
Cek1p
C. albicans Required for filamentous growth Leberer et al. (1996)
Ubc4p, U. maydis Required for filamentous growth, Mayorga and
Ubc5p,
Ubc3p/Fuz7p
mating and pheromone production Gold (1999)
Protein kinase A Bcy1p, S. cerevisiae Required for pseudohyphal differentiation Reviewed in
components Tpk1p,
Tpk3p,
Tpk2p
Lengeler et al. (2000)
Tpk2 C. albicans Regulates filamentous growth Lengeler et al. (2000)
Uac1p, U. maydis Required to activate filamentous growth Gold et al. (1994);
Ubc1p
Mayorga and
Gold (1999)
(Yaar et al. 1997; Ushinsky et al. 2002). Ashbya
gossypii is a morphologically simple mycelial
fungus, and recent studies of AgRSR1 have shown
that it is not required for the establishment of
hyphal polarisation during spore germination.
It is, however, important for maintenance of
polarisation during hyphal growth and is localised
at the tips of growing hyphae (Bauer et al. 2004). In
more complex mycelial fungi, even less is known
but the A. gossypii data suggest that selection of
polarisation sites may not be solely due to RSR1
orthologues.
3. Bud Emergence
S. cerevisiae GTP-bound Cdc42p regulates the establishment
of polarised growth by recruiting additional
proteins to the bud site (reviewed in Johnson
1999). After bud site selection, GTP-bound
Cdc42p dissociates from both Cdc24p and Bem1p
proteins and interacts with Gic1p, Gic2p and members
of the family of p21-activated kinases (PAKs;
reviewed in Brown et al. 1997; Johnson 1999; Richman
et al. 1999). This complex binds to the Bni1p
formin, which acts as a scaffold protein and binds
a number of additional proteins including phosphorylated
myosins and actin-associated proteins
(Evangelista et al. 1997; Lechler et al. 2000; Fig. 1.5).
This complex at the incipient bud site promotes the
consequent localisation of the septin, chitin and
myosin rings, and actin polymerisation at the bud
tip (Lechler et al. 2000; Gladfelter et al. 2004; Kadota
et al. 2004).
Different cell types can exhibit different cell
cycle characteristics, and there is a close interplay
between regulatory mechanisms which control cell
growth and polarisation and cell cycle progression.
Cell cycle control is imposed during budding by