teins can bind their chromophores (FAD and
retinal, respectively) (Bieszke et al. 1999a, b),
light-dependent gene expression is not altered
in the knockout strains grown under vegetative
conditions (Chen et al. 2009; Froehlich et al.
2010). Moreover, N. crassa possesses two
genes (phy-1 and phy-2) with similarities to
red light-responsive phytochromes (Galagan
et al. 2003). Although further studies must be
performed to confirm PHY-1 and PHY-2proteins as bona fide active photoreceptors, it
has also been reported that the amplitude of
blue light induction for some genes such as
con-10 are affected in a phy-2 null mutant
(Olmedo et al. 2010), suggesting the existence
of a connection between blue and red light
photoreceptors in N. crassa.
An interplay between both wavelengths is
better understood by pioneering studies performed in Aspergillus nidulans (Idnurm and
Heitman 2005). In this saprophytic fungus, sexual/asexual development is tightly controlled
by light. Thus, red light is sensed by the phytochrome FphA, inducing conidiation and inhibiting the formation of fruiting bodies
(Blumenstein et al. 2005). Despite FphA being
able to coordinate biliverdin in vitro, the
endogenous chromophore is still a mystery.
On the other hand, the WC-1 and WC-2 orthologs LreA and LreB interact to form the WCClike complex involved in blue light perception,
which increases the generation of conidiospores but also activates the formation of reproductive structures. In order to do this, FphA
binds to the LreA/LreB heterodimer in the
nucleus (Purschwitz et al. 2008), forming a
larger complex involved in balancing the action
of both wavelengths. Notably, the repressor role
of red light-activated FphA is mediated by its
target protein VeA, which also interacts with
several proteins that form the Velvet complex
(Bayram et al. 2010). The latter includes LaeA, a
protein with a major role in the production of
secondary metabolites. For this reason, VeA is
considered a bridge in the regulation of relevant biological processes such as life cycle and
secondary metabolism by light (Bayram et al.
2010). Interestingly, the phenotype of a veA
knockout strain is partially restored by complementation with a N. crassa ortholog (Bayram
et al. 2008).
Light responses have also been studied in
the fungus Botrytis cinerea, which is a relevant
pathogen in the agroindustry due to its capacity
to infect many plant species (Dean et al. 2012).
In that context, a bioinformatic analysis
revealed that its genome encodes for 11 photoreceptors (Schumacher 2017), but only few of
these have been studied in detail. As it could be
expected, photoreception in B. cinerea is based
on functional WC-1 and WC-2 proteins
(BcWCL1 and BcWCL2, respectively). Just as
in N. crassa, these orthologs interact in the
nuclei (Schumacher 2012) forming the B.
cinerea White Collar Complex (BcWCC). The
BcWCC is key in regulating the circadian clock
of this phytopathogen, providing daily rhythms
of its virulence on plant hosts (Hevia et al.
2015). Yet unexpectedly, while some genes
loose regulation by light in the absence of
BcWCL1, others appear to remain lightresponsive, which contrasts the essential role
that WC-1 plays in N. crassa (Canessa et al.
2013). Additionally, the photochemical properties of a B. cinerea VVD homolog (BcVVD1)
have been studied, being bcvvd1 one of the
genes regulated by light in a BcWCC-dependent
manner (Canessa et al. 2013). However, unlike
the N. crassa protein, BcVVD1 does not show
homodimerization in response to blue light
(Foley et al. 2018). Moreover, the existence of
a photoadaptation process mediated by
BcVVD1/BcWCL-1 interaction is not clear yet
in B. cinerea. Recently, another LOVcontaining photoreceptor with unique features
has been described in B. cinerea. The BcLOV4
protein contains a polybasic amphipathic helix
between the LOV domain and the carboxylterminus of the protein, which is rapidly
recruited to the plasma membrane upon illumination and interacts with anionic phospholipids in an unspecific way (Glantz et al. 2018).
Notably, this work presented the first natural
photoreceptor with the capacity to associate
with membrane components by light (Glantz
et al. 2018).
In contrast to B. cinerea, photoadaptation is
well-studied in T. reesei, in which it occurs in a
similar way to N. crassa. Several studies have
shown that light modifies the physiology of T.
reesei, including its striking ability to degrade
cellulose (Schmoll 2018). Specifically, the
12 Exploiting Fungal Photobiology as a Source of Novel Bio-blocks for Optogenetic Systems
311
retinal, respectively) (Bieszke et al. 1999a, b),
light-dependent gene expression is not altered
in the knockout strains grown under vegetative
conditions (Chen et al. 2009; Froehlich et al.
2010). Moreover, N. crassa possesses two
genes (phy-1 and phy-2) with similarities to
red light-responsive phytochromes (Galagan
et al. 2003). Although further studies must be
performed to confirm PHY-1 and PHY-2proteins as bona fide active photoreceptors, it
has also been reported that the amplitude of
blue light induction for some genes such as
con-10 are affected in a phy-2 null mutant
(Olmedo et al. 2010), suggesting the existence
of a connection between blue and red light
photoreceptors in N. crassa.
An interplay between both wavelengths is
better understood by pioneering studies performed in Aspergillus nidulans (Idnurm and
Heitman 2005). In this saprophytic fungus, sexual/asexual development is tightly controlled
by light. Thus, red light is sensed by the phytochrome FphA, inducing conidiation and inhibiting the formation of fruiting bodies
(Blumenstein et al. 2005). Despite FphA being
able to coordinate biliverdin in vitro, the
endogenous chromophore is still a mystery.
On the other hand, the WC-1 and WC-2 orthologs LreA and LreB interact to form the WCClike complex involved in blue light perception,
which increases the generation of conidiospores but also activates the formation of reproductive structures. In order to do this, FphA
binds to the LreA/LreB heterodimer in the
nucleus (Purschwitz et al. 2008), forming a
larger complex involved in balancing the action
of both wavelengths. Notably, the repressor role
of red light-activated FphA is mediated by its
target protein VeA, which also interacts with
several proteins that form the Velvet complex
(Bayram et al. 2010). The latter includes LaeA, a
protein with a major role in the production of
secondary metabolites. For this reason, VeA is
considered a bridge in the regulation of relevant biological processes such as life cycle and
secondary metabolism by light (Bayram et al.
2010). Interestingly, the phenotype of a veA
knockout strain is partially restored by complementation with a N. crassa ortholog (Bayram
et al. 2008).
Light responses have also been studied in
the fungus Botrytis cinerea, which is a relevant
pathogen in the agroindustry due to its capacity
to infect many plant species (Dean et al. 2012).
In that context, a bioinformatic analysis
revealed that its genome encodes for 11 photoreceptors (Schumacher 2017), but only few of
these have been studied in detail. As it could be
expected, photoreception in B. cinerea is based
on functional WC-1 and WC-2 proteins
(BcWCL1 and BcWCL2, respectively). Just as
in N. crassa, these orthologs interact in the
nuclei (Schumacher 2012) forming the B.
cinerea White Collar Complex (BcWCC). The
BcWCC is key in regulating the circadian clock
of this phytopathogen, providing daily rhythms
of its virulence on plant hosts (Hevia et al.
2015). Yet unexpectedly, while some genes
loose regulation by light in the absence of
BcWCL1, others appear to remain lightresponsive, which contrasts the essential role
that WC-1 plays in N. crassa (Canessa et al.
2013). Additionally, the photochemical properties of a B. cinerea VVD homolog (BcVVD1)
have been studied, being bcvvd1 one of the
genes regulated by light in a BcWCC-dependent
manner (Canessa et al. 2013). However, unlike
the N. crassa protein, BcVVD1 does not show
homodimerization in response to blue light
(Foley et al. 2018). Moreover, the existence of
a photoadaptation process mediated by
BcVVD1/BcWCL-1 interaction is not clear yet
in B. cinerea. Recently, another LOVcontaining photoreceptor with unique features
has been described in B. cinerea. The BcLOV4
protein contains a polybasic amphipathic helix
between the LOV domain and the carboxylterminus of the protein, which is rapidly
recruited to the plasma membrane upon illumination and interacts with anionic phospholipids in an unspecific way (Glantz et al. 2018).
Notably, this work presented the first natural
photoreceptor with the capacity to associate
with membrane components by light (Glantz
et al. 2018).
In contrast to B. cinerea, photoadaptation is
well-studied in T. reesei, in which it occurs in a
similar way to N. crassa. Several studies have
shown that light modifies the physiology of T.
reesei, including its striking ability to degrade
cellulose (Schmoll 2018). Specifically, the
12 Exploiting Fungal Photobiology as a Source of Novel Bio-blocks for Optogenetic Systems
311