A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, fungi, which is separate from .. “The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for. A glimpse into the basis of vision in the kingdom Mycota. Idnurm A(1), Verma S, Corrochano LM. Author information: (1)Division of Cell Biology. Virtually all organisms exposed to light are capable of sensing this environmental signal. In recent years the photoreceptors that mediate the.
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Virtually all organisms exposed to light are capable of sensing this environmental signal. The small sizes of fungal genomes and ease in genetic and molecular biology manipulations make this kingdom ideal amongst the eukaryotes for understanding kinhdom.
Classification of Division Mycota | Fungi
The most widespread and conserved photosensory protein in the fungi is White collar 1 WC-1a flavin-binding photoreceptor that mycotaa with WC-2 as a transcription factor complex. Other photosensory proteins in fungi include opsins, phytochromes and cryptochromes whose roles in fungal photobiology are not fully resolved and their distribution in the fungi requires further taxon sampling.
Additional unknown photoreceptors await discovery. This review discusses the effects of light on fungi and the evolutionary processes that may have shaped the ability of species to kycota and respond to this signal. The ability to see is considered a key sense in humans and, as such, extensive research mcyota addressed the mechanisms and evolution of the photosensory properties in humans and animals. In plants and other photosynthetic organisms, sensing light is required to adapt to the available energy source provided by the sun, and photosensory proteins are also well studied in these groups Briggs and Spudich, The fungi represent the third group kingsom macroscopic eukaryotes, and they are the sibling kingdom to the animals.
Fungi have also been studied for their ability to sense light, their responses, and the molecular basis of light-sensing. With small genome sizes relative to plants kingxom animals, advances in genome sequencing provide gene content information on numerous and phylogenetically-diverse fungal species. In addition, genetic oingdom protocols are available for many fungal species, enabling gene functions to be tested specifically by the creation of mutant strains and observing the phenotypes of these mutants.
The application of these resources and recent studies enable a glimpse into the evolution of the molecular basis of vision in this eukaryotic kingdom. A kingdm question is why fungi would benefit from sensing light, as they do not use light for photosynthesis or to see adjacent objects.
The main selective pressures are likely protection against DNA damage caused by ultraviolet wavelengths, timing spore release, directional discharge of spores, and as a clue for nutrient availability in the environment. These original roles have been elaborated upon such that the responses of fungi to light are now diverse and often species dependent. No general assumptions can be made about the effects of light on a species being newly investigated.
Kingdom Mycota or Fungi: General characteristics and classification
However, one common feature is changes in spore production in response to light. Given the role of spores in fungal dissemination in the wild, understanding light-sensing mgcota of practical interest because of the potential to control spread of fungi in nature. Additional practical applications of studying fungal photobiology include i the link between light-sensing and virulence in pathogenic species, ii photoregulation of secondary metabolite biosynthesis and enzyme production, iii the effects of light on commercial mushroom cultivation, and iv the use of fungal photoreceptors for experimentation in other organisms.
The molecular basis behind light-sensing in fungi is an active area of research, and the subject has been reviewed recently Corrochano, ; Herrera-Estrella and Horwitz, ; Purschwitz et al. This issue of Fungal Genetics and Biology provides an additional set of reviews on specific topics of fungal photobiology. Collectively, these articles demonstrate the high level of research productivity.
Here, we update developments on known photoreceptors with a focus on evolution of light-sensing, and place an emphasis on White collar 1 because of its widely established conserved role in blue-light sensing. We highlight areas that are unresolved, but potentially important, for further understanding light-sensing in fungi. The fungi last shared a common ancestor perhaps more than a billion years ago, as based on fossil and molecular clock evidence, and had certainly diverged into the current extant major lineages million years ago Taylor and Berbee, How many or what percentage of the estimated 1.
Interpolating reports in the literature indicates that the majority of species, with some notable and major exceptions like the Saccharomycotina yeasts, respond to light. Indeed, a review on the topic of light-responses in fungi from fifty years ago already includes more than species Marsh et al. Changes in emphases since the s were towards discovering effective wavelengths, which revealed that responses often occur with blue light but can occur over the full visible spectrum, the analysis of physiological and biochemical responses, and identification of the genes and proteins required for light-sensing Corrochano and Avalos, ; Tisch and Schmoll, Photosensory proteins are defined as those that regulate a signal transduction pathway Briggs and Spudich, As other non-sensory proteins use the same cofactors found in photoreceptors, these proteins can be affected by light and elicit a response to light, and yet not function in a sensory fashion Hug, ; Hug, However, this distinction can be a grey area, as for example in distinguishing between overlapping sensory and DNA repair roles of some of the cryptochrome-photolyase proteins.
A second ambiguous area of photosensor function is whether they have both light and dark regulatory roles. Other considerations are that light can cause changes in the composition of growth medium that may affect fungal behavior, and the possible role of damaging wavelengths or photon intensities on the response of species.
The genome of S. However, light affected S. Even more striking was the ability to entrain S. Effects of light on Saccharomycotina relatives of S. Distribution of photosensory proteins and their copy numbers in species across the fungal kingdom, based on whole-genome sequence information.
Wherever mycita, a representative example is provided rather than all sequenced members of a clade eg. Fusariumthe Saccharomycotina yeasts, Schizosaccharomyces, Microsporum and Trichophyton. The terms zygomycete and chytrid do not refer to monophyletic groups. For the cryptochrome category, the CPD-photolyase class is not included but see Bayram et al.
The gold standard for demonstrating a photosensory function is a multistep process. First, a light-response is observed.
Second, the efficiency of that response is measured over a range of wavelengths to generate an action spectrum of the response either crudely into broad color groups eg. Third, the photosensor gene and protein are identified eg. Fourth, the light response must be impaired by mutating the gene. Fifth, the photosensory protein is purified and characterized to demonstrate that it has the same absorption spectrum as the phenotypic action spectrum in step 2, as well as enabling the identification of the associated chromophore.
Note that all known photosensory proteins function by interacting with a photoreactive molecule eg. Sixth, the photosensor function must explain the phenotypes observed, in that it should regulate genes or proteins specifically required for the responses.
Clearly, this is a multidisciplinary process and often only partially achieved. For the best-studied fungus, Neurospora crassayears passed from the first observation of a response to light to characterization of purified WC-1 protein Fig.
From response to receptor: These events demonstrate the multidimensional process of demonstrating a protein is a photoreceptor. Different properties of fungi are influenced by light exposure to enable their success in the wild.
The original selective pressure for light-sensing was protection against damaging light, as illustrated by induction of photolyase genes or pigmentation by light in highly-diverged species. However, the benefit of avoiding harmful irradiation must be balanced by the chemoorganoheterotrophic physiology of fungi.
Members of this kingdom acquire nutrients from organic material, and this material relies directly or indirectly on light as an energy source and to fix carbon through photosynthesis. A second process often regulated by light is an increase in pigments such as carotenoids or melanins. In some fungi the spores themselves are pigmented, and sporulation may also be co-regulated with the biosynthesis of secondary metabolites. The role of pigment is likely protection against ultraviolet damage, as mutant strains affected in genes required for pigment biosynthesis are more sensitive than wild type to UV light eg.
Several species of fungi have phototropic responses such that they bend towards or away from a source of light. In others, development is controlled such that fruiting structures are positioned towards the light for spore release, like the perithecial beaks in N. Some of the best and most spectacular examples of phototropism are in the Mucormycotina in which the asexual sporangiophores bend towards blue wavelengths.
For Pilobolus species, the sporangiophore formation is also under circadian clock control Schmidle, ; Uebelmesser, and the spore mass is forcibly discharged towards the rising sun. Similar phototropism occurs in Phycomyces blakesleeanus and Mucor circinelloidesand wc-1 homologs mediate the photosensory process in these two species and probably in Pilobolus Idnurm et al.
An unexplained link exists between light-sensing and fungal pathogenicity Idnurm and Crosson, In human pathogens, virulence of Histoplasma capsulatum is affected by prior exposure to light Campbell and Berliner,while wc-1 mutant strains of Cryptocococcus neoformans and F. Other studies suggest links between light exposure and virulence in insect pathogens.
Spores of Metarhizium anisopliae formed under blue light are more pathogenic towards Galleria mellonella wax moth larvae Alves et al. For example, in the pathogenic interaction of Rhizophydium planktonicum on Asterionella formosathe diatom is responsible for the attachment of chytrid zoospores in response to light. This was illustrated by killing the diatoms and showing that the chytrid zoospores no longer attached to the dead diatoms under light conditions Canter and Jaworski, The underlying basis for light-sensing or wc-1 affecting fungal virulence remains to be elucidated.
Although light-sensing is common in fungi, the effects may not always be obvious and may be difficult to identify. Passaging and specific selection for conveniently-behaved laboratory strains can be a factor. For example, the effects of light on the circadian clock are enhanced in N. The function of phytochrome in light-sensing in Aspergillus nidulans was masked by the veA mutation that causes constitutive conidiation under all light regimes Blumenstein et al.
Some effects of light may be subtle, counteracted by exposure to the full visible spectrum, or best detected at specific developmental stages. Finally, there appears to be good evidence for the absence of light-sensing in some fungal species, most notably in ascomycete yeast species eg.
As such, the absence of a light response may be a real biological property. In searching for an effect of light, it is worth testing sporulation or pigmentation in a set of wild type strains, rather than use a single laboratory-preferred wild type. An alternative approach is to compare the transcript profile of the fungus grown in the dark or exposed to light: A third approach is to explore changes in protein abundance or post-translational modifications such as phosphorylation.
A glimpse into the basis of vision in the kingdom Mycota
The Mycota encode in their genomes representatives of major classes of photosensor known from other organisms, that is the opsins, phytochromes and cryptochromes. Fungi also contain proteins with light-sensing LOV domains that are discussed in section 4. While some species encode all types in their genome, most photoreceptors show a sporadic distribution across the kingdom Fig.
Access to genome sequencing information enables a broad search for candidate photosensors in fungi. The broad distribution of photosensing across the major domains of life underscores the importance light-sensing has in biology. In the following section what is known about three photoreceptors type in fungi will be described. First reported from a fungus a decade ago Bieszke et al. Biochemical analysis of heterologously-expressed fungal opsins shows that these proteins could function as either sensors in the case of N.
Phenotypes associated with mutating the N. A whole genome transcript profile in N. However, mutation of the nop-1 gene derepresses the N.
Mhcota analysis of opsins in F. An opsin is clearly implicated in phototaxis of the chytrid Allomyces reticulatus because the action spectrum of phototaxis shifts away from the normal green wavelengths when the organism is grown in retinal analogs Saranak and Foster, Surprisingly, the draft genome sequence of Allomyces macrogynus does not contain an obvious type I for classification see Spudich et al.