Photoactivated Adenylyl Cyclase Controls Phototaxis in the Flagellate Euglena gracilis Photoactivated Adenylyl Cyclase Controls Phototaxis in the Flagellate Euglena gracilis

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Abstract

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 (RNA) 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 photo taxis 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.

Journal

  • Plant Physiology = Plant Physiology

    Plant Physiology = Plant Physiology 133(4), 1517-1521, 2003-12

    American Society of Plant Biologists

Codes

  • NII Article ID (NAID)
    120006576053
  • Text Lang
    ENG
  • Article Type
    journal article
  • ISSN
    0032-0889
  • Data Source
    IR 
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