Biomedical Engineering Reference
In-Depth Information
carA
gene product phytoene synthase, giving as a fi nal result an increase
in the amount of β-carotene produced in the pathway (Eslava et al. 1974,
Tagua et al unpublished results). The second group is represented by
phenols (Cerdá-Olmedo and Hütterman 1986), such as dimethyl phthalate
or veratrol, which are potent stimulators (Bejarano et al 1988). In other
phenols such as cinnamic alcohol or thymol the stimulation is accomplished
by an inhibition of the phytoene dehydrogenase. They are synergic with
retinol in appropriate strains, indicating that they have independent action
mechanisms (Bejarano and Cerdá-Olmedo 1989). Retinols and phenols
are inactive in
Blakeslea
but carotenogenesis in this fungus is activated by
β-ionone and several other compounds (Lampila et al. 1985).
A separate group of chemical activators in the Mucorales are the
trisporoids, whose name is derived from trisporic acid, isolated fi rst from
B. trispora
as a substance increasing β-carotene production in mated cultures
of this fungus (Caglioti et al. 1966).
Light Regulation
Blue light stimulates carotenogenesis in many fungi (Avalos et al. 1993,
Corrochano and Garre 2010) including
Phycomyces
(Bejarano et al. 1991)
and
Mucor
(Navarro et al. 1995, Velayos et al. 1997).
Blakeslea
produces
less carotenes under continuous illumination than in the dark (Sutter
1970). However later analyses have shown that photo-induced carotene
accumulation is observed under appropriate light regimes (Quiles-Rosillo
et al. 2005).
In
Phycomyces
, the most studied fungus of the Mucorales, the fl uence-
response curves for light induced carotenogenesis show two components
with different thresholds: one at low light intensity and another at high
light intensity (Jayaram et al. 1979, 1980, Bejarano et al. 1991). Blue light
leads to an increased accumulation of the mRNAs from
carRA
and
carB
genes (Ruiz-Hidalgo et al. 1997, Blasco et al. 2001, Sanz et al, 2010), as
it does for homologous genes of other fungi, such as
M. circinelloides
(Velayos et al. 2000a, b),
B. trispora
(Quiles-Rosillo et al. 2005) and
N. crassa
(Nelson et al 1989, Schidmidhauser et al. 1990, 1994). The large collection
of
Phycomyces
mutants available includes strains which are altered in
photocarotenogenesis. Among them there are blind mutants (genotype
mad
)
(Bergman et al. 1973, Cerdá-Olmedo and Corrochano 2001).
Recently, the analysis of the
Phycomyces
genome allowed the
identifi cation of
madA
and
madB
as White-Collar coding genes (Idnurm et al.
2006, Sanz et al. 2009) (fi gure 4). The MadA and MadB proteins are required
for normal carotenoid photo-induction (Bergman et al. 1973, Jayaram et
al. 1980) indicating a light induced activation mechanism mediated by a
WC-like complex. Similar genes have been found in
Mucor circinelloides
