Dataset Information

Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii.

ABSTRACT: We demonstrate that two rhodopsins, identified from cDNA sequences, function as low- and high-light-intensity phototaxis receptors in the eukaryotic alga Chlamydomonas reinhardtii. Each of the receptors consists of an approximately 300-residue seven-transmembrane helix domain with a retinal-binding pocket homologous to that of archaeal rhodopsins, followed by approximately 400 residues of additional membrane-associated portion. The function of the two rhodopsins, Chlamydomonas sensory rhodopsins A and B (CSRA and CSRB), as phototaxis receptors is demonstrated by in vivo analysis of photoreceptor electrical currents and motility responses in transformants with RNA interference (RNAi) directed against each of the rhodopsin genes. The kinetics, fluence dependencies, and action spectra of the photoreceptor currents differ greatly in transformants in accord with the relative amounts of photoreceptor pigments expressed. The data show that CSRA has an absorption maximum near 510 nm and mediates a fast photoreceptor current that saturates at high light intensity. In contrast, CSRB absorbs maximally at 470 nm and generates a slow photoreceptor current saturating at low light intensity. The relative wavelength dependence of CSRA and CSRB activity in producing phototaxis responses matches precisely the wavelength dependence of the CSRA- and CSRB-generated currents, demonstrating that each receptor mediates phototaxis. The saturation of the two photoreceptor currents at different light fluence levels extends the range of light intensity to which the organism can respond. Further, at intensities where both operate, their light signals are integrated at the level of membrane depolarization caused by the two photoreceptor currents.

SUBMITTER: Sineshchekov OA

PROVIDER: S-EPMC124360 | biostudies-literature | 2002 Jun

REPOSITORIES: biostudies-literature

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Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii.

Sineshchekov Oleg A OA Jung Kwang-Hwan KH Spudich John L JL

Proceedings of the National Academy of Sciences of the United States of America 20020611 13

We demonstrate that two rhodopsins, identified from cDNA sequences, function as low- and high-light-intensity phototaxis receptors in the eukaryotic alga Chlamydomonas reinhardtii. Each of the receptors consists of an approximately 300-residue seven-transmembrane helix domain with a retinal-binding pocket homologous to that of archaeal rhodopsins, followed by approximately 400 residues of additional membrane-associated portion. The function of the two rhodopsins, Chlamydomonas sensory rhodopsins ...[more]

PMID: 12060707

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Project description:Autophagy plays a role in regulating important cellular functions in response to stress conditions. The role of nitric oxide (NO) in the regulation of autophagy in Chlamydomonas reinhardtii has been not studied. Illumination of C. reinhardtii cells under a high light (HL, 1,600 ?mol m-2 s-1) condition induced a NO burst through NO synthase- and nitrate reductase-independent routes, and cell death. The abundance of CrATG8 protein, an autophagy marker of C. reinhardtii, increased after HL illumination along with a linear increase in the transcript abundance of autophagy-associated genes (CrVPS34, CrATG1, CrATG3, CrATG4, CrATG6, CrATG7, CrATG8, and CrATG12), which were suppressed in the presence of an NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). The cells were treated with NO donors, S-nitroso-N-acetyl-penicillamine, and S-nitrosoglutathione, under a normal light (50 ?mol m-2 s-1) condition to elucidate the role of NO in autophagy activation and cell death. Treatment with 0.05 mM or 0.1 mM NO donors increased the abundance of ATG8 protein and CrATG transcripts, which were suppressed in the presence of cPTIO. Moreover, treatment with 0.05 mM NO donors did not affect cell viability, while 0.1 mM NO donors elicited a transient decrease in cell growth and death that recovered after 12 h. The transient effect could be prevented by the presence of cPTIO. However, treatment with 1 mM H2O2 and 0.1 mM NO donors enhanced autophagy induction and resulted in cell death after 24 h. The interaction of H2O2 and NO can be prevented by cPTIO treatment. This implies that NO is critical for the interaction of H2O2 and NO that induces cell death and autophagy. Furthermore, exposure to 0.1 mM NO donors under a non-lethal HL condition (750 ?mol m-2 s-1) evoked autophagy and cell death. In conclusion, the present findings demonstrated that the NO-mediated autophagy pathway is activated in C. reinhardtii under lethal high intensity illumination and may interact with H2O2 for HL-induced cell death. The relationships between autophagy and cell death are discussed.

Dataset Information

Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii.

Publications

Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii.

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