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Youngho Chung - One of the best experts on this subject based on the ideXlab platform.
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cyanobacterial phytochrome cph2 is a negative regulator in Phototaxis toward uv a
FEBS Letters, 2011Co-Authors: Yoonjung Moon, Kwanghwan Jung, Jongsoon Choi, Young Mok Park, Youngho ChungAbstract:We investigated the wavelength dependence and photon-fluence rate response relationship for Phototaxis of wild-type and a cyanobacterial phytochrome 2 (cph2) mutant in cyanobacterium Synechocystis sp. PCC 6803. Compared to wild-type, the cph2 mutant exhibited maximal activity for positive Phototaxis at the near-UV spectral range. Two cysteine to serine substitutions in two chromophore-binding domains showed a similar cph2 mutant phenotype under UV-A. Epistasis of a pixJ mutation over a cph2 mutation implied that pixJ gene acts downstream of the cph2 gene with respect to UV-A-induced positive Phototaxis. Therefore, we suggest that Cph2 is essential for the inhibition of positive Phototaxis toward UV-A.
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the role of cyanopterin in uv blue light signal transduction of cyanobacterium synechocystis sp pcc 6803 Phototaxis
Plant and Cell Physiology, 2010Co-Authors: Yoonjung Moon, Young Mok Park, Young Shik Park, Won Il Chung, Youngho ChungAbstract:We analyzed the effects of inactivating the pteridine glycosyltransferase gene (pgtA) on the photomovement of the cyanobacterium Synechocystis sp. PCC 6803 under different light conditions. The pgtA mutant displayed abnormal photomovement under UV-A/blue light. In particular, the pgtA mutant showed a negative phototactic response under UV-A (315-400 nm), whereas the wild-type did not show any photomovement. Inhibition of pterin biosynthesis by N-acetylserotonin (NAS), an inhibitor of sepiapterin reductase, also inhibited a positive phototactic response of the wild-type under white and blue light. In addition, negative Phototaxis of the pgtA mutant was observed under UV-A/blue light in the presence of NAS. These results indicated that the product of the PgtA enzyme, cyanopterin, is involved in the inhibition of the negative Phototaxis of the wild-type by sensing the UV-A. However, 2,4-diamino-6-hydroxypyrimidine-mediated inhibition of GTP cyclohydrolase I, the rate-limiting enzyme for pterin biosynthesis, significantly increased the positive Phototaxis toward UV-A in the wild-type and the pgtA mutant. Furthermore, we measured the action spectrum of Phototaxis in vivo for the wild-type and pgtA mutant. Maximal activity of the wild-type was at 300, 380 and 440 nm, indicating absorption by pterins and flavin. In particular, the UV-A/ blue peak at 380 and 440 nm obtained from the action spectrum of Phototaxis was found to be closely correlated with the in vitro absorption spectrum previously reported for the cyanobacterial cryptochrome DASH. By investigating the photomovement of the wild-type and pgtA mutant to UV and blue light, we suggest that pterin can function as the chromophore of putative UV/blue photoreceptor(s) in cyanobacterial Phototaxis.
Gaspar Jekely - One of the best experts on this subject based on the ideXlab platform.
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Phototaxis and the origin of visual eyes
bioRxiv, 2015Co-Authors: Nadine Randel, Gaspar JekelyAbstract:Vision allows animals to detect spatial differences in environmental light levels. High-resolution image-forming eyes evolved from low-resolution eyes via increases in photoreceptor cell number, improvements in optics and changes in the neural circuits that process spatially resolved photoreceptor input. However, the evolutionary origins of the first low-resolution visual systems have been unclear. We propose that the lowest-resolving (two-pixel) visual systems could initially have functioned in visual Phototaxis. During visual Phototaxis, such elementary visual systems compare light on either side of the body to regulate phototactic turns. Another, even simpler and non-visual strategy is characteristic of helical Phototaxis, mediated by sensory-motor eyespots. The recent mapping of the complete neural circuitry (connectome) of an elementary visual system in the larva of the annelid Platynereis dumerilii sheds new light on the possible paths from non-visual to visual Phototaxis and to image-forming vision. We outline an evolutionary scenario focusing on the neuronal circuitry to account for these transitions. We also present a comprehensive review of the structure of phototactic eyes in invertebrate larvae and assign them to the non-visual and visual categories. We propose that non-visual systems may have preceded visual phototactic systems in evolution that in turn may have repeatedly served as intermediates during the evolution of image-forming eyes.
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spectral tuning of Phototaxis by a go opsin in the rhabdomeric eyes of platynereis
Current Biology, 2015Co-Authors: Martin Guhmann, Nadine Randel, Csaba Veraszto, Luis A Bezarescalderon, Nico K Michiels, Shozo Yokoyama, Gaspar JekelyAbstract:Summary Phototaxis is characteristic of the pelagic larval stage of most bottom-dwelling marine invertebrates [1]. Larval Phototaxis is mediated by simple eyes that can express various types of light-sensitive G-protein-coupled receptors known as opsins [2–8]. Since opsins diversified early during metazoan evolution in the marine environment [9], understanding underwater light detection could elucidate this diversification. Opsins have been classified into three major families, the r-opsins, the c-opsins, and the Go/RGR opsins, a family uniting Go-opsins, retinochromes, RGR opsins, and neuropsins [10, 11]. The Go-opsins form an ancient and poorly characterized group retained only in marine invertebrate genomes. Here, we characterize a Go-opsin from the marine annelid Platynereis dumerilii [3–5, 12–15]. We found Go-opsin1 coexpressed with two r-opsins in depolarizing rhabdomeric photoreceptor cells in the pigmented eyes of Platynereis larvae. We purified recombinant Go-opsin1 and found that it absorbs in the blue-cyan range of the light spectrum. To characterize the function of Go-opsin1, we generated a Go-opsin1 knockout Platynereis line by zinc-finger-nuclease-mediated genome engineering. Go-opsin1 knockout larvae were phototactic but showed reduced efficiency of Phototaxis to wavelengths matching the in vitro Go-opsin1 spectrum. Our results highlight spectral tuning of Phototaxis as a potential mechanism contributing to opsin diversity.
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evolution of Phototaxis
Philosophical Transactions of the Royal Society B, 2009Co-Authors: Gaspar JekelyAbstract:Phototaxis in the broadest sense means positive or negative displacement along a light gradient or vector. Prokaryotes most often use a biased random walk strategy, employing type I sensory rhodopsin photoreceptors and two-component signalling to regulate flagellar reversal. This strategy only allows Phototaxis along steep light gradients, as found in microbial mats or sediments. Some filamentous cyanobacteria evolved the ability to steer towards a light vector. Even these cyanobacteria, however, can only navigate in two dimensions, gliding on a surface. In contrast, eukaryotes evolved the capacity to follow a light vector in three dimensions in open water. This strategy requires a polarized organism with a stable form, helical swimming with cilia and a shading or focusing body adjacent to a light sensor to allow for discrimination of light direction. Such arrangement and the ability of three-dimensional phototactic navigation evolved at least eight times independently in eukaryotes. The origin of three-dimensional Phototaxis often followed a transition from a benthic to a pelagic lifestyle and the acquisition of chloroplasts either via primary or secondary endosymbiosis. Based on our understanding of the mechanism of Phototaxis in single-celled eukaryotes and animal larvae, it is possible to define a series of elementary evolutionary steps, each of potential selective advantage, which can lead to pelagic phototactic navigation. We can conclude that it is relatively easy to evolve Phototaxis once cell polarity, ciliary swimming and a stable cell shape are present.
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mechanism of Phototaxis in marine zooplankton
Nature, 2008Co-Authors: Gaspar Jekely, Julien Colombelli, Harald Zur Hausen, Ernst H K Stelzer, Francois Nedelec, Detlev ArendtAbstract:The simplest animal eyes are eyespots composed of two cells only: a photoreceptor and a shading pigment cell. They resemble Darwin’s ‘proto-eyes’, considered to be the first eyes to appear in animal evolution1,2,3,4. Eyespots cannot form images but enable the animal to sense the direction of light. They are characteristic for the zooplankton larvae of marine invertebrates and are thought to mediate larval swimming towards the light. Phototaxis of invertebrate larvae contributes to the vertical migration of marine plankton5, which is thought to represent the biggest biomass transport on Earth6,7. Yet, despite its ecological and evolutionary importance, the mechanism by which eyespots regulate Phototaxis is poorly understood. Here we show how simple eyespots in marine zooplankton mediate phototactic swimming, using the marine annelid Platynereis dumerilii as a model8. We find that the selective illumination of one eyespot changes the beating of adjacent cilia by direct cholinergic innervation resulting in locally reduced water flow. Computer simulations of larval swimming show that these local effects are sufficient to direct the helical swimming trajectories towards the light. The computer model also shows that axial rotation of the larval body is essential for Phototaxis and that helical swimming increases the precision of navigation. These results provide, to our knowledge, the first mechanistic understanding of Phototaxis in a marine zooplankton larva and show how simple eyespots regulate it. We propose that the underlying direct coupling of light sensing and ciliary locomotor control was a principal feature of the proto-eye and an important landmark in the evolution of animal eyes.
Devaki Bhaya - One of the best experts on this subject based on the ideXlab platform.
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light matters Phototaxis and signal transduction in unicellular cyanobacteria
Molecular Microbiology, 2004Co-Authors: Devaki BhayaAbstract:Summary Many photosynthetic microorganisms have evolved the ability to sense light quality and/or quantity and can steer themselves into optimal conditions within the environment. Phototaxis and gliding motility in unicellular cyanobacteria require type IV pili, which are multifunctional cell surface appendages. Screens for cells exhibiting aberrant motility uncovered several non-motile mutants as well as some that had lost positive Phototaxis (consequently, they were negatively phototactic). Several negatively phototactic mutants mapped to the tax 1 locus, which contains five chemotaxis-like genes. This locus includes a gene that encodes a putative photoreceptor (TaxD1) for positive Phototaxis. A second chemotaxis-like cluster ( tax3 locus) appears to be involved in pilus biogenesis. The biosynthesis and regulation of type IV pilus-based motility as well as the communication between the pilus motor and photosensory molecules appear to be complex and tightly regulated. Furthermore, the discovery that cyclic AMP and novel gene products are necessary for Phototaxis/motility suggests that there might be additional levels of communication and signal processing.
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multiple light inputs control Phototaxis in synechocystis sp strain pcc6803
Journal of Bacteriology, 2003Co-Authors: Wingon Ng, Arthur R Grossman, Devaki BhayaAbstract:The phototactic behavior of individual cells of the cyanobacterium Synechocystis sp. strain PCC6803 was studied with a glass slide-based Phototaxis assay. Data from fluence rate-response curves and action spectra suggested that there were at least two light input pathways regulating Phototaxis. We observed that positive Phototaxis in wild-type cells was a low fluence response, with peak spectral sensitivity at 645 and 704 nm. This red-light-induced Phototaxis was inhibited or photoreversible by infrared light (760 nm). Previous work demonstrated that a taxD1 mutant (Cyanobase accession no. sll0041; also called pisJ1) lacked positive but maintained negative Phototaxis. Therefore, the TaxD1 protein, which has domains that are similar to sequences found in both bacteriophytochrome and the methyl-accepting chemoreceptor protein, is likely to be the photoreceptor that mediates positive Phototaxis. Wild-type cells exhibited negative Phototaxis under high-intensity broad-spectrum light. This phenomenon is predominantly blue light responsive, with a maximum sensitivity at approximately 470 nm. A weakly negative phototactic response was also observed in the spectral region between 600 and 700 nm. A ΔtaxD1 mutant, which exhibits negative Phototaxis even under low-fluence light, has a similar action maximum in the blue region of the spectrum, with minor peaks from green to infrared (500 to 740 nm). These results suggest that while positive Phototaxis is controlled by the red light photoreceptor TaxD1, negative Phototaxis in Synechocystis sp. strain PCC6803 is mediated by one or more (as yet) unidentified blue light photoreceptors.
Yoonjung Moon - One of the best experts on this subject based on the ideXlab platform.
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cyanobacterial phytochrome cph2 is a negative regulator in Phototaxis toward uv a
FEBS Letters, 2011Co-Authors: Yoonjung Moon, Kwanghwan Jung, Jongsoon Choi, Young Mok Park, Youngho ChungAbstract:We investigated the wavelength dependence and photon-fluence rate response relationship for Phototaxis of wild-type and a cyanobacterial phytochrome 2 (cph2) mutant in cyanobacterium Synechocystis sp. PCC 6803. Compared to wild-type, the cph2 mutant exhibited maximal activity for positive Phototaxis at the near-UV spectral range. Two cysteine to serine substitutions in two chromophore-binding domains showed a similar cph2 mutant phenotype under UV-A. Epistasis of a pixJ mutation over a cph2 mutation implied that pixJ gene acts downstream of the cph2 gene with respect to UV-A-induced positive Phototaxis. Therefore, we suggest that Cph2 is essential for the inhibition of positive Phototaxis toward UV-A.
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the role of cyanopterin in uv blue light signal transduction of cyanobacterium synechocystis sp pcc 6803 Phototaxis
Plant and Cell Physiology, 2010Co-Authors: Yoonjung Moon, Young Mok Park, Young Shik Park, Won Il Chung, Youngho ChungAbstract:We analyzed the effects of inactivating the pteridine glycosyltransferase gene (pgtA) on the photomovement of the cyanobacterium Synechocystis sp. PCC 6803 under different light conditions. The pgtA mutant displayed abnormal photomovement under UV-A/blue light. In particular, the pgtA mutant showed a negative phototactic response under UV-A (315-400 nm), whereas the wild-type did not show any photomovement. Inhibition of pterin biosynthesis by N-acetylserotonin (NAS), an inhibitor of sepiapterin reductase, also inhibited a positive phototactic response of the wild-type under white and blue light. In addition, negative Phototaxis of the pgtA mutant was observed under UV-A/blue light in the presence of NAS. These results indicated that the product of the PgtA enzyme, cyanopterin, is involved in the inhibition of the negative Phototaxis of the wild-type by sensing the UV-A. However, 2,4-diamino-6-hydroxypyrimidine-mediated inhibition of GTP cyclohydrolase I, the rate-limiting enzyme for pterin biosynthesis, significantly increased the positive Phototaxis toward UV-A in the wild-type and the pgtA mutant. Furthermore, we measured the action spectrum of Phototaxis in vivo for the wild-type and pgtA mutant. Maximal activity of the wild-type was at 300, 380 and 440 nm, indicating absorption by pterins and flavin. In particular, the UV-A/ blue peak at 380 and 440 nm obtained from the action spectrum of Phototaxis was found to be closely correlated with the in vitro absorption spectrum previously reported for the cyanobacterial cryptochrome DASH. By investigating the photomovement of the wild-type and pgtA mutant to UV and blue light, we suggest that pterin can function as the chromophore of putative UV/blue photoreceptor(s) in cyanobacterial Phototaxis.
Shinji Masuda - One of the best experts on this subject based on the ideXlab platform.
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the patan chey like response regulator pixe interacts with the motor atpase pilb1 to control negative Phototaxis in the cyanobacterium synechocystis sp pcc 6803
Plant and Cell Physiology, 2020Co-Authors: Annik Jakob, Yuki Sugimoto, Hiroshi Nakamura, Atsuko Kobayashi, Annegret Wilde, Shinji MasudaAbstract:: The cyanobacterium Synechocystis sp. PCC 6803 can move directionally on a moist surface toward or away from a light source to reach optimal light conditions for its photosynthetic lifestyle. This behavior, called Phototaxis, is mediated by type IV pili (T4P), which can pull a single cell into a certain direction. Several photoreceptors and their downstream signal transduction elements are involved in the control of Phototaxis. However, the critical steps of local pilus assembly in positive and negative Phototaxis remain elusive. One of the photoreceptors controlling negative Phototaxis in Synechocystis is the blue-light sensor PixD. PixD forms a complex with the CheY-like response regulator PixE that dissociates upon illumination with blue light. In this study, we investigate the phototactic behavior of pixE deletion and overexpression mutants in response to unidirectional red light with or without additional blue-light irradiation. Furthermore, we show that PixD and PixE partly localize in spots close to the cytoplasmic membrane. Interaction studies of PixE with the motor ATPase PilB1, demonstrated by in vivo colocalization, yeast two-hybrid and coimmunoprecipitation analysis, suggest that the PixD-PixE signal transduction system targets the T4P directly, thereby controlling blue-light-dependent negative Phototaxis. An intriguing feature of PixE is its distinctive structure with a PATAN (PatA N-terminus) domain. This domain is found in several other regulators, which are known to control directional Phototaxis. As our PilB1 coimmunoprecipitation analysis revealed an enrichment of PATAN domain response regulators in the eluate, we suggest that multiple environmental signals can be integrated via these regulators to control pilus function.
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genetics of the blue light dependent signal cascade that controls Phototaxis in the cyanobacterium synechocystis sp pcc6803
Plant and Cell Physiology, 2016Co-Authors: Yuki Sugimoto, Hiroshi Nakamura, Koichi Hori, Shinji MasudaAbstract:: The Synechocystis sp. PCC6803 can move on a solid surface in response to light, a phenomenon called Phototaxis. Although many of the photoreceptors involved in Phototaxis have been identified, the mechanisms that regulate directional motility of Synechocystis are not well understood. Previous studies showed that a mutant lacking the blue light-using flavin (BLUF) photoreceptor PixD exhibits negative Phototaxis under conditions where the wild type responds positively. PixD interacts with the pseudo-response regulator-like protein PixE in a light-dependent manner, suggesting that this intermolecular interaction is important for Phototaxis regulation, although genetic evidence has been lacking. To gain further insight into Phototaxis regulation by PixD-PixE signaling, we constructed the deletion mutants ΔPixE and ΔPixD-ΔPixE, and characterized their phenotypes, which matched those of the wild type (positive Phototaxis). Because ΔPixD exhibited negative Phototaxis, PixE must function downstream of PixD. Under intense blue light (>100 μmol m-2 s-1; 470 nm) the wild type exhibited negative Phototaxis, but ΔPixD-PixE exhibited positive Phototaxis toward low-intensity blue light (∼0.8 μmol m-2 s-1; 470 nm). These results suggest that an unknown light-sensing system(s), that is necessary for directional cell movement, can be activated by low-intensity blue light; on the other hand, PixD needs high-intensity blue light to be activated. We also isolated spontaneous mutants that compensated for the pixE deletion. Genome-wide sequencing of the mutants revealed that the uncharacterized gene sll2003 regulates positive and negative Phototaxis in response to light intensity.
