Photoactivated adenylyl cyclase controls phototaxis in the flagellate Euglena gracilis

• Published in: Plant physiology (Bethesda) Vol. 133; no. 4; pp. 1517 - 1521
• Main Authors: Ntefidou, M, Iseki, M, Watanabe, M, Lebert, M, Hader, D.P
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01-12-2003; American Society of Plant Physiologists; The American Society for Plant Biologists
• Series: Focus Issue on Light Signaling
• Subjects: adenylate cyclase; Adenylyl Cyclases - metabolism; Adenylyl Cyclases - radiation effects; algae and seaweeds; Animals; Astasia; Astasia longa; Base Sequence; Biological and medical sciences; Cell motion; Cell physiology; Cell tracking; Chloroplasts; Chloroplasts - physiology; DNA Primers; Double stranded RNA; Enzyme Activation; Euglena; Euglena gracilis; Euglena gracilis - physiology; Euglena gracilis - radiation effects; Flagella - physiology; Focus Issue on Light Signaling; Freshwater; Fundamental and applied biological sciences. Psychology; Kinetics; Light; Light sources; Lighting; Mastigophora; Messenger RNA; Molecular and cellular biology; molecular sequence data; Movement - physiology; Movement - radiation effects; nucleotide sequences; paraxonemal body; Photoactivated adenylyl cyclase; photoorientation; Photoreceptor Cells - physiology; Photoreceptor Cells - radiation effects; Photoreceptors; Phototaxis; Plant physiology and development; plant proteins; RNA; RNA interference; Time Factors; Vision, photoreception; Euglenophyta; Enzyme; Photoactivation; Algae; Genetic variant; Photoreceptor; Phosphorus-oxygen lyases; Lyases; Structure function relationship; Adenylate cyclase; Regulation(control); Phototaxis; Euglena gracilis; Photophobia; Taxis; Intraspecific comparison; Mutation; Photoregulation; Thallophyta
• DOI: 10.1104/pp.103.034223
• EISSN: 1532-2548
• ISSN: 0032-0889

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.