Abstract:Many responses of the zygomycete fungus Phycomyces blakesleeanus are mediated by blue light, e.g. the stimulation of beta-carotene synthesis (photocarotenogenesis) and the formation of fruiting bodies (photomorphogenesis). Even though both responses have been described in detail genetically and biophysically, the underlying molecular events remain unknown. Applying a pharmacological approach in developing mycelia, we investigated the possible involvement of heterotrimeric G proteins in the blue-light transduct… Show more
“…The madA-dependent induction of wcoA is similar to the situation of the N. crassa vivid gene, which encodes a LOV-domain protein that mediates photoadaptation and is also light regulated through the WC-1 photoreceptor (33,34). The other madB and madC strains could have mutations in wc-2 homologs or in fungal blue-light receptors, such as cryptochromes or G protein-coupled receptors (44). The madD-madJ mutants are predicted to correspond to genes encoding products controlling signaling events downstream of light detection and͞or to regulate the function of the photoreceptors themselves (2,45).…”
Phycomyces blakesleeanus is a filamentous zygomycete fungus that produces striking elongated single cells that extend up to 10 cm into the air, with each such sporangiophore supporting a sphere containing the spores for dispersal. This organism has served as a model for the detection of environmental signals as diverse as light, chemicals, touch, wind, gravity, and adjacent objects. In particular, sporangiophore growth is regulated by light, and it exhibits phototropism by bending toward near-UV and blue wavelengths and away from far-UV wavelengths in a manner that is physiologically similar to plant phototropic responses. The Phycomyces madA mutants were first isolated more than 40 years ago, and they exhibit reduced sensitivity to light. Here, we identify two (duplicated) homologs in the White Collar 1 family of blue-light photoreceptors in Phycomyces. We describe that the madA mutant strains contain point mutations in one of these genes and that these mutations cosegregate with a defect in phototropism after genetic crosses. Thus, the phototropic responses of fungi through madA and plants through phototropin rely on diverse proteins; however, these proteins share a conserved flavin-binding domain for photon detection.
“…The madA-dependent induction of wcoA is similar to the situation of the N. crassa vivid gene, which encodes a LOV-domain protein that mediates photoadaptation and is also light regulated through the WC-1 photoreceptor (33,34). The other madB and madC strains could have mutations in wc-2 homologs or in fungal blue-light receptors, such as cryptochromes or G protein-coupled receptors (44). The madD-madJ mutants are predicted to correspond to genes encoding products controlling signaling events downstream of light detection and͞or to regulate the function of the photoreceptors themselves (2,45).…”
Phycomyces blakesleeanus is a filamentous zygomycete fungus that produces striking elongated single cells that extend up to 10 cm into the air, with each such sporangiophore supporting a sphere containing the spores for dispersal. This organism has served as a model for the detection of environmental signals as diverse as light, chemicals, touch, wind, gravity, and adjacent objects. In particular, sporangiophore growth is regulated by light, and it exhibits phototropism by bending toward near-UV and blue wavelengths and away from far-UV wavelengths in a manner that is physiologically similar to plant phototropic responses. The Phycomyces madA mutants were first isolated more than 40 years ago, and they exhibit reduced sensitivity to light. Here, we identify two (duplicated) homologs in the White Collar 1 family of blue-light photoreceptors in Phycomyces. We describe that the madA mutant strains contain point mutations in one of these genes and that these mutations cosegregate with a defect in phototropism after genetic crosses. Thus, the phototropic responses of fungi through madA and plants through phototropin rely on diverse proteins; however, these proteins share a conserved flavin-binding domain for photon detection.
“…Pertussis toxin (Sigma‐Aldrich, St. Louis, MO 63178, USA) was dissolved in sterile water, kept at 4°C and used within 2 weeks, as described by Tsolakis et al. (2004).…”
Summary
Previous studies revealed that blue light stimulates and red light inhibits prehaustoria development in young seedlings of the parasitic weed Cuscuta campestris (field dodder). This study showed a positive correlation between blue light induced increases in inositol 1,4,5‐trisphosphate (IP3) and blue light‐mediation of prehaustoria development, prior to host attachment. Blue light induced a significant increase in the level of IP3, with a peak at about 30 min. Thereafter, the level of IP3 declined to the resting value after 2 h of blue light. Irradiation with 10 min red light pulse applied directly at the end of each 0.05, 0.1, 0.15, 0.2, 0.3, 1, 2 and 4 h blue light significantly reduced IP3, while high levels of IP3 were observed after 10 min far‐red pulse. The G‐protein inhibitor pertussis toxin inhibited prehaustoria developed under blue light, suggesting that receptor‐coupled G‐proteins are likely to be involved in prehaustoria development. These results are the first in vivo demonstration of a possible role for IP3 as a second messenger in the blue light signal transduction process in prehaustoria development in Cuscuta.
“…Yet it shows clear enhancement after illumination of dark-grown mycelia in this fungus (Quiles-Rosillo et al 2005). With respect to regulation, it is interesting that in Phycomyces , a heterotrimeric G-protein apparently plays a role photocarotenogenesis (Tsolakis et al 2004). Fig.…”
Section: Metabolic Pathways As Output Pathways Of Light Signalingmentioning
Light represents a major carrier of information in nature. The molecular machineries translating its electromagnetic energy (photons) into the chemical language of cells transmit vital signals for adjustment of virtually every living organism to its habitat. Fungi react to illumination in various ways, and we found that they initiate considerable adaptations in their metabolic pathways upon growth in light or after perception of a light pulse. Alterations in response to light have predominantly been observed in carotenoid metabolism, polysaccharide and carbohydrate metabolism, fatty acid metabolism, nucleotide and nucleoside metabolism, and in regulation of production of secondary metabolites. Transcription of genes is initiated within minutes, abundance and activity of metabolic enzymes are adjusted, and subsequently, levels of metabolites are altered to cope with the harmful effects of light or to prepare for reproduction, which is dependent on light in many cases. This review aims to give an overview on metabolic pathways impacted by light and to illustrate the physiological significance of light for fungi. We provide a basis for assessment whether a given metabolic pathway might be subject to regulation by light and how these properties can be exploited for improvement of biotechnological processes.
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