expression of a cellobiohydrolase encoding
gene (cbh-1) is a light-regulated process
(Gyalai-Korpos et al. 2010). In the same way,
as occurs in the fungi mentioned above, the
orthologs of WC-1 and WC-2 (BLR1 and
BLR2) are key to command the light responses
in T. reesei, by forming a WCC-like complex
(Castellanos et al. 2010). One of the genes regulated by the light-dependent activity of the
BLR1/BLR2 complex is the vvd ortholog env1,
that encodes a protein involved in photoadaptation to constant illumination as well as other
signaling pathways such as growth, reproduction, nutrient metabolism, response to stresses,
and biosynthesis of specific molecules (Schmoll
et al. 2005; Seibel et al. 2012). Moreover, a
variety of photoreceptors have been identified
in the T. reesei genome, including a cryptochrome, a phytochrome, and an opsin (Martinez et al. 2008).
Nonetheless, fungal photobiology is not
exclusive for ascomycete species. Bioinformatic
analyses of available basidiomycete, zygomycete, and chytrid genomes have found several
orthologs of described fungal photoreceptors
(Idnurm et al. 2010). In fact, WCC-,
cryptochrome-, opsin-, and phytochromeencoding genes have been identified in basidiomycetes such as Coprinopsis cinerea, Cryptococcus neoformans, Ustilago maydis, and
Puccinia graminis (Salichos and Rokas 2010;
Corrochano 2019). Furthermore, cellular processes, such as phototropism of fruiting bodies,
development of sexual structures, and activation of carotenogenesis have been related to
light regulation in the zygomycete fungi Phycomyces blakesleeanus, Mucor circinelloides,
and Rhizopus delemar (Corrochano and Garre
2010; Corrochano 2019). Notably, unlike ascomycete and basidiomycete species, each one of
these zygomycetes has multiple homolog genes
to the WC-1 photoreceptor and its partner WC2 (Corrochano and Garre 2010). Even the chytridiomycete Spizellomyces punctatus possesses WCC components and a phytochrome
(Corrochano 2019).
As it has become clear throughout this
chapter, many of the reported optogenetic
experiences have been obtained in yeast, utilizing a wide range of optogenetic modules coming from different organisms, with just few
experiences using fungal bio-blocks such as
VVD and WC-1 LOV domains from N. crassa
(Fig. 12.5). Although diverse (and even antagonistic) biological processes depending on WCC
proteins appear to be well-spread in fungi, a
conserved role of this complex in photoreception processes is nevertheless clear. In contrast,
the presence of VVD orthologs seems to be
infrequent, suggesting that it may not be a
vital element of the machinery involved in
light-responses across different fungal phyla.
This latter opens the exciting possibility of
using the LOV domain of Neurospora VVD as
well as a cognate promoter to control biological
processes by blue light in those fungi that do
not possess it naturally. On the other hand,
genes encoding cryptochromes, opsin, and
phytochromes also have been reported in several fungal organisms. Therefore, a wide repertoire of fungal photoreceptors is available for
the implementation of new optogenetic tools,
expanding the current toolbox of this discipline.
The study of light-controlled processes
requires, yet, the ability to properly control
experimental light conditions. Thus, whether
conducting studies aimed at further exploring
the photobiology of fungal species (i.e., N.
crassa, A. nidulans, T. reesei, B. cinerea, etc.),
or implementing optogenetic switches in yeast
or other fungi, it is important to have a proper
setup that allows tight control of full darkness
or defined light stimuli. Thus, a customized
darkroom is recommended, containing incubators that can set defined photocycles and light
intensities, equipped with safety-red lights
(when manipulating blue light optogenetic systems), and conditions securing manipulation of
samples in full darkness when needed
(Fig. 12.6).
IV. Concluding Remarks
In past years, synthetic biologists have begun to
interrogate different cell processes by a new set
of light-controlled tools. Light acts as an
orthogonal, non-toxic, and inexpensive modu312
V. Rojas et al.
gene (cbh-1) is a light-regulated process
(Gyalai-Korpos et al. 2010). In the same way,
as occurs in the fungi mentioned above, the
orthologs of WC-1 and WC-2 (BLR1 and
BLR2) are key to command the light responses
in T. reesei, by forming a WCC-like complex
(Castellanos et al. 2010). One of the genes regulated by the light-dependent activity of the
BLR1/BLR2 complex is the vvd ortholog env1,
that encodes a protein involved in photoadaptation to constant illumination as well as other
signaling pathways such as growth, reproduction, nutrient metabolism, response to stresses,
and biosynthesis of specific molecules (Schmoll
et al. 2005; Seibel et al. 2012). Moreover, a
variety of photoreceptors have been identified
in the T. reesei genome, including a cryptochrome, a phytochrome, and an opsin (Martinez et al. 2008).
Nonetheless, fungal photobiology is not
exclusive for ascomycete species. Bioinformatic
analyses of available basidiomycete, zygomycete, and chytrid genomes have found several
orthologs of described fungal photoreceptors
(Idnurm et al. 2010). In fact, WCC-,
cryptochrome-, opsin-, and phytochromeencoding genes have been identified in basidiomycetes such as Coprinopsis cinerea, Cryptococcus neoformans, Ustilago maydis, and
Puccinia graminis (Salichos and Rokas 2010;
Corrochano 2019). Furthermore, cellular processes, such as phototropism of fruiting bodies,
development of sexual structures, and activation of carotenogenesis have been related to
light regulation in the zygomycete fungi Phycomyces blakesleeanus, Mucor circinelloides,
and Rhizopus delemar (Corrochano and Garre
2010; Corrochano 2019). Notably, unlike ascomycete and basidiomycete species, each one of
these zygomycetes has multiple homolog genes
to the WC-1 photoreceptor and its partner WC2 (Corrochano and Garre 2010). Even the chytridiomycete Spizellomyces punctatus possesses WCC components and a phytochrome
(Corrochano 2019).
As it has become clear throughout this
chapter, many of the reported optogenetic
experiences have been obtained in yeast, utilizing a wide range of optogenetic modules coming from different organisms, with just few
experiences using fungal bio-blocks such as
VVD and WC-1 LOV domains from N. crassa
(Fig. 12.5). Although diverse (and even antagonistic) biological processes depending on WCC
proteins appear to be well-spread in fungi, a
conserved role of this complex in photoreception processes is nevertheless clear. In contrast,
the presence of VVD orthologs seems to be
infrequent, suggesting that it may not be a
vital element of the machinery involved in
light-responses across different fungal phyla.
This latter opens the exciting possibility of
using the LOV domain of Neurospora VVD as
well as a cognate promoter to control biological
processes by blue light in those fungi that do
not possess it naturally. On the other hand,
genes encoding cryptochromes, opsin, and
phytochromes also have been reported in several fungal organisms. Therefore, a wide repertoire of fungal photoreceptors is available for
the implementation of new optogenetic tools,
expanding the current toolbox of this discipline.
The study of light-controlled processes
requires, yet, the ability to properly control
experimental light conditions. Thus, whether
conducting studies aimed at further exploring
the photobiology of fungal species (i.e., N.
crassa, A. nidulans, T. reesei, B. cinerea, etc.),
or implementing optogenetic switches in yeast
or other fungi, it is important to have a proper
setup that allows tight control of full darkness
or defined light stimuli. Thus, a customized
darkroom is recommended, containing incubators that can set defined photocycles and light
intensities, equipped with safety-red lights
(when manipulating blue light optogenetic systems), and conditions securing manipulation of
samples in full darkness when needed
(Fig. 12.6).
IV. Concluding Remarks
In past years, synthetic biologists have begun to
interrogate different cell processes by a new set
of light-controlled tools. Light acts as an
orthogonal, non-toxic, and inexpensive modu312
V. Rojas et al.