Discovery of signaling effect of UV-B/C light in the extended UV-A/blue-type action spectra for step-down and step-up photophobic responses in the unicellular flagellate algaEuglena gracilis

Matsunaga, Shigeru; Hori, Takafumi; Takahashi, Tetsuo; Kubota, Mamoru; Watanabe, Masakatsu; Okamoto, Kazushi; Masuda, Kazuaki; Sugai, Manabu

doi:10.1007/bf01280710

Cited by 34 publications

(25 citation statements)

References 38 publications

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“…Using the Okazaki large spectrograph and a computerized video motion analysis, Matsunaga and coworkers found that in addition to UV-A and blue light the action spectrum for photophobic responses of E. gracilis extended well into the UV-B with peaks at 270 nm (step-down response) and 280 nm (step-up response), respectively (Matsunaga et al 1998) which they attributed to the combined action of 6-biopterin and FAD. In addition, fluorescence and emission spectra of the isolated PAB proteins indicated that pterins might also be involved ).…”

Section: Earlier Results and Hypothesesmentioning

confidence: 97%

Photomovement in Euglena

Häder

Iseki

2017

Advances in Experimental Medicine and Biology

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Motile microorganisms such as the green Euglena gracilis use a number of external stimuli to orient in their environment. They respond to light with photophobic responses, photokinesis and phototaxis, all of which can result in accumulations of the organisms in suitable habitats. The light responses operate synergistically with gravitaxis, aerotaxis and other responses. Originally the microscopically obvious stigma was thought to be the photoreceptor, but later the paraxonemal body (PAB, paraflagellar body) has been identified as the light responsive organelle, located in the trailing flagellum inside the reservoir. The stigma can aid in light direction perception by shading the PAB periodically when the cell rotates helically in lateral light, but stigmaless mutants can also orient with respect to the light direction, and negative phototaxis does not need the presence of the stigma. The PAB is composed of dichroically oriented chromoproteins which is reflected in a pronounced polarotaxis in polarized light. There was a long debate about the potential photoreceptor molecule in Euglena, including carotenoids, flavins and rhodopsins. This discussion was terminated by the unambiguous proof that the photoreceptor is a 400 kDa photoactivated adenylyl cyclase (PAC) which consists of two α- and two β-subunits each. Each subunit possesses two BLUF (Blue Light receptor Using FAD) domains binding FAD, which harvest the light energy, and two adenylyl cyclases, which produce cAMP from ATP. The cAMP has been found to activate one of the five protein kinase s found in Euglena (PK.4). This enzyme in turn is thought to phosphorylate proteins inside the flagellum which result in a change in the flagellar beating pattern and thus a course correction of the cell. The involvements of PAC and protein kinase have been confirmed by RNA interference (RNAi). PAC is responsible for step-up photophobic responses as well as positive and negative phototaxis, but not for the step-down photophobic response, even though the action spectrum of this resembles those for the other two responses. Analysis of several colorless Euglena mutants and the closely related Euglena longa (formerly Astasia longa) confirms the results. Photokinesis shows a completely different action spectrum. Some other Euglena species, such as E. sanguinea and the gliding E. mutabilis, have been investigated, again showing totally different action spectra for phototaxis and photokinesis as well as step-up and step-down photophobic responses.

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Section: Earlier Results and Hypothesesmentioning

confidence: 97%

Photomovement in Euglena

Häder

Iseki

2017

Advances in Experimental Medicine and Biology

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“…The overall similarity between PAC␣ and PAC␤ is 72% at the nucleotide level. Reverse genetics (RNA interference [RNAi]; see below) revealed that PAC is not the photoreceptor of step-down photophobic responses (Iseki et al, 2002), which is consistent with the different action spectrum of this response (Matsunaga et al, 1998). The photoreceptor of phototaxis was up to now also unknown, but action spectroscopy suggested the involvement of flavins and pterins (Brodhun and Häder, 1990;Häder and Lebert, 1998).…”

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confidence: 80%

Photoactivated Adenylyl Cyclase Controls Phototaxis in the Flagellate Euglena gracilis

et al. 2003

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Euglena gracilis, a unicellular freshwater protist exhibits different photomovement responses, such as phototaxis (oriented movement toward or away from the light source) and photophobic (abrupt turn in response to a rapid increase [step-up] or decrease [step-down] in the light fluence rate) responses. Photoactivated adenylyl cyclase (PAC) has been isolated from whole-cell preparations and identified by RNA interference (RNAi) to be the photoreceptor for step-up photophobic responses but not for step-down photophobic responses (M. Iseki, S. Matsunaga, A. Murakami, K. Ohno, K. Shiga, C. Yoshida, M. Sugai, T. Takahashi, T. Hori, M. Watanabe [2002] Nature 415: 1047-1051). The present study shows that knockdown of PAC by RNAi also effectively suppresses both positive and negative phototaxis, indicating for the first time that PAC or a PAC homolog is also the photoreceptor for photoorientation of wild-type E. gracilis. Recovery from RNAi occurred earlier for step-up photophobic responses than for positive and negative phototaxis. In addition, we investigated several phototaxis mutant strains of E. gracilis with different cytological features regarding the stigma and paraxonemal body (PAB; believed to be the location for the phototaxis photoreceptor) as well as Astasia longa, a close relative of E. gracilis. All of the E. gracilis mutant strains had PAC mRNAs, whereas in A. longa, a different but similar mRNA was found and designated AlPAC. Consistently, all of these strains showed no phototaxis but performed step-up photophobic responses, which were suppressed by RNAi of the PAC mRNA. The fact that some of these strains possess a cytologically altered or no PAB demonstrates that at least in these strains, the PAC photoreceptor responsible for the step-up photophobic responses is not located in the PAB.The protist Euglena gracilis, a unicellular freshwater flagellate, is capable of both autotrophy and heterotrophy. The cell is characterized (Fig. 1A) by one flagellum emerging from the reservoir (invagination of the anterior plasma membrane) and a second nonemerging flagellum. The paraxonemal body (PAB) is a photosensing organelle (Ghetti et al., 1985) located inside the reservoir close to the connecting point of the two flagella. The stigma, formerly known as the eyespot, is positioned inside the cytoplasm and adjacent to the PAB. It contains carotenoids and is not involved in photosensing, as initially thought, but contributes to photoorientation (Lebert and Häder, 1997) by shading the PAB as the cell rotates around its longitudinal axis during forward swimming. A detailed description of E. gracilis can be found in Buetow (1968).E. gracilis uses light and gravity for orientation to move to and stay at optimal growth conditions in the water column. Light-induced responses can be categorized into photokinesis, a light-dependent swimming velocity; phototaxis, an oriented movement toward (positive phototaxis) or away (negative phototaxis) from the light source (Häder et al., 1981); and photophobic responses (Mikolaj...

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“…1A, PAC activity (1 ng ml −1 in the reaction mixture) increased proportionally to photon fluence rates in the range of 2-50 lmol m −2 s and became nearly saturated in the range of 50-100 lmol m −2 s −1 . Ranges of photon fluence rates were equivalent to those that induce physiological responses in Euglena, such as the step-up photophobic response 15 and photodispersal of several mutant strains. 16 …”

Section: Dependency On Photon Fluence Ratesmentioning

confidence: 99%

Kinetic analysis of the activation of photoactivated adenylyl cyclase (PAC), a blue-light receptor for photomovements of Euglena

Yoshikawa

Suzuki

Watanabe

et al. 2005

Photochem Photobiol Sci

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Photoactivated adenylyl cyclase (PAC) was first purified from a photosensing organelle (the paraflagellar body) of the unicellular flagellate Euglena gracilis, and is regarded as the photoreceptor for the step-up photophobic response. Here, we report the kinetic properties of photoactivation of PAC and a change in intracellular cAMP levels upon blue light irradiation. Activation of PAC was dependent both on photon fluence rate and duration of irradiation, between which reciprocity held well in the range of 2-50 lmol m −2 s −1 (total fluence of 1200 lmol m −2 ). Intermittent irradiation also caused activation of PAC in a photon fluence-dependent manner irrespective of cycle periods. Wavelength dependency of PAC activation showed prominent peaks in the UV-B/C, UV-A and blue regions of the spectrum. The time course of the changes in intracellular cAMP levels corresponded well with that of the step-up photophobic response. From this and the kinetic properties of PAC photoactivation, we concluded that an increase in intracellular cAMP levels evoked by photoactivation of PAC is a key event of the step-up photophobic response.

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Discovery of signaling effect of UV-B/C light in the extended UV-A/blue-type action spectra for step-down and step-up photophobic responses in the unicellular flagellate algaEuglena gracilis

Cited by 34 publications

References 38 publications

Photomovement in Euglena

Photomovement in Euglena

Photoactivated Adenylyl Cyclase Controls Phototaxis in the Flagellate Euglena gracilis

Kinetic analysis of the activation of photoactivated adenylyl cyclase (PAC), a blue-light receptor for photomovements of Euglena

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