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PubMed2005

[Advances in cryptocromes and their signal transduction].

Cryptochromes are blue light receptors which share the similar function with the phytochromes in regulation of the growth and development in plants. After 90's, especially in the recent years, profound studies have been carried around the cryptochromes. Cryptochromes were found not only in plants, but also in animals. It has been known that cryptochromes are involved in de-etiolation in seed germination, photoperiodic-inductive flowering, regulation of circadian rhythm, etc. In the article, we introduced the characteristics of cryptochromes and the genes, including cryptochromes structure, the presence in plant kingdom, the localization in cells, and the expression regulated by light. In addition, the function of cryptochrome in plant photomorphogenesis and in controlling of the circadian clock in plants and animals was summarized. Through analysis of the relationships between cryptochromes and the interacted proteins, we clarified primarily the roles of how cryptochromes mediate the plant growth and development via interacting with proteins in the signal pathway. It was suggested that studying the cryptochromes and their signal transduction profoundly to disclose the nature of plant photomorphogenesis will be of great importance both to biologic theory as well as application.

Animals↗
PubMed2002

Tales from the crypt(ochromes).

Cryptochromes are a family of flavoproteins found in organisms ranging from Arabidopsis to man. Across phylogeny, these proteins have been used for pleiotropic functions ranging from blue-light-dependent development in plants and blue-light-mediated phase shifting of the circadian clock in insects to a core circadian clock component in mammals. Review of the roles of cryptochromes in model organisms reveals several common themes: Multiple cryptochrome family members within individual organisms have redundant functions; cryptochromes used in photic entrainment pathways of the circadian clock are partially redundant with other photopigments; and cryptochromes may function in circadian phototransduction and core clock mechanisms in the same organism, with different functions in different tissues. The present review summarizes recent research on the functions of cryptochrome in the circadian timekeeping and photic entrainment pathways.

Animals↗
PubMed2003

PP7 is a positive regulator of blue light signaling in Arabidopsis.

The cryptochrome blue light photoreceptors mediate various photomorphogenic responses in plants, including hypocotyl elongation, cotyledon expansion, and control of flowering time. The molecular mechanism of cryptochrome function in Arabidopsis is becoming increasingly clear, with recent studies showing that both CRY1 and CRY2 are localized in the nucleus and that CRY2 is regulated by blue light-dependent phosphorylation. Despite these advances, no positive cryptochrome signaling component has been identified to date. Here, we demonstrate that a novel Ser/Thr protein phosphatase (AtPP7) with high sequence similarity to the Drosophila retinal degeneration C protein phosphatase acts as an intermediate in blue light signaling. Transgenic Arabidopsis seedlings with reduced AtPP7 expression levels exhibit loss of hypocotyl growth inhibition and display limited cotyledon expansion in response to blue light irradiation. These effects are as striking as those seen in hy4 mutant seedlings, which are deficient in CRY1. We further demonstrate that AtPP7 transcript levels are not rate limiting and that AtPP7 probably acts downstream of cryptochrome in the nucleus, ensuring signal flux through the pathway. Based on our findings and recent data regarding cryptochrome action, we propose that AtPP7 acts as a positive regulator of cryptochrome signaling in Arabidopsis.

Arabidopsis↗
PubMed2000

A quadruple photoreceptor mutant still keeps track of time.

Time measurement and light detection are inextricably linked. Cryptochromes, the blue-light photoreceptors shared between plants and animals, are critical for circadian rhythms in flies and mice [1-3]. WC-1, a putative blue-light photoreceptor, is also essential for the maintenance of circadian rhythms in Neurospora [4]. In contrast, we report here that in Arabidopsis thaliana the double mutant lacking the cryptochromes cry1 and cry2, and even a quadruple mutant lacking the red/ far-red photoreceptor phytochromes phyA and phyB as well as cry1 and cry2, retain robust circadian rhythmicity. Interestingly, the quadruple mutant was nearly blind for developmental responses but perceived a light cue for entraining the circadian clock. These results indicate that cryptochromes and phytochromes are not essential components of the central oscillator in Arabidopsis and suggest that plants could possess specific photosensory mechanisms for temporal orientation, in addition to cryptochromes and phytochromes, which are used for both spatial and temporal adaptation.

Arabidopsis↗
PubMed2000

Plant blue-light receptors.

Plants have several blue-light receptors, which regulate different aspects of growth and development. Recent studies have identified three such receptors: cryptochrome 1, cryptochrome 2 and phototropin. Cryptochromes 1 and 2 are photolyase-like receptors that regulate hypocotyl growth and flowering time; phototropin mediates phototropism in response to blue light. In addition, phytochrome A has also been found to mediate various blue-light responses. Although the signal-transduction mechanisms of blue-light receptors remain largely unclear, phototropin is probably a protein kinase that regulates cytoplasmic calcium concentrations, whereas the cryptochromes might regulate anion-channel activity and changes in gene expression.

Arabidopsis↗
PubMed2006

A cryptochrome/photolyase class of enzymes with single-stranded DNA-specific photolyase activity.

Photolyases and cryptochrome blue-light photoreceptors are evolutionarily related flavoproteins that perform distinct functions. Photolyases repair UV-damaged DNA in many species from bacteria to plants and animals. Cryptochromes regulate growth and development in plants and the circadian clock in animals. Recently, a new branch of the photolyase/cryptochrome family was identified. Members of this branch exhibited no or trace levels of DNA repair activity in vivo and in vitro and, therefore, were considered to be cryptochromes, and they were named cryptochrome-DASH. Here, we show that Cry-DASH proteins from bacterial, plant, and animal sources actually are photolyases with high degree of specificity for cyclobutane pyrimidine dimers in ssDNA.

Animals↗
PubMed2000

Interacting molecular loops in the mammalian circadian clock.

We show that, in the mouse, the core mechanism for the master circadian clock consists of interacting positive and negative transcription and translation feedback loops. Analysis of Clock/Clock mutant mice, homozygous Period2(Brdm1) mutants, and Cryptochrome-deficient mice reveals substantially altered Bmal1 rhythms, consistent with a dominant role of PERIOD2 in the positive regulation of the Bmal1 loop. In vitro analysis of CRYPTOCHROME inhibition of CLOCK: BMAL1-mediated transcription shows that the inhibition is through direct protein:protein interactions, independent of the PERIOD and TIMELESS proteins. PERIOD2 is a positive regulator of the Bmal1 loop, and CRYPTOCHROMES are the negative regulators of the Period and Cryptochrome cycles.

ARNTL Transcription Factors↗
PubMed2004

Effect of vitamin A depletion on nonvisual phototransduction pathways in cryptochromeless mice.

Mice exhibit multiple nonvisual responses to light, including 1) photoentrainment of circadian rhythm; 2) "masking," which refers to the acute effect of light on behavior, either negative (activity suppressing) or positive (activity inducing); and 3) pupillary constriction. In mammals, the eye is the sole photosensory organ for these responses, and it contains only 2 known classes of pigments: opsins and cryptochromes. No individual opsin or cryptochrome gene is essential for circadian photoreception, gene photoinduction, or masking. Previously, the authors found that mice lacking retinol-binding protein, in which dietary depletion of ocular retinaldehyde can be achieved, had normal light signaling to the SCN, as determined by per gene photoinduction. In the present study, the authors analyzed phototransduction to the SCN in vitamin A-replete and vitamin A-depleted rbp-/- and rbp-/-cry1-/-cry2-/- mice using molecular and behavioral end points. They found that vitamin A-depleted rbp-/- mice exhibit either normal photoentrainment or become diurnal. In contrast, while vitamin A-replete rbp-/-cry1-/-cry2-/- mice are light responsive (with reduced sensitivity), vitamin A-depleted rbp-/-cry1-/-cry2-/- mice, which presumably lack functional opsins and cryptochromes, lose most behavioral and molecular responses to light. These data demonstrate that both cryptochromes and opsins regulate nonvisual photoresponses.

Animals↗
PubMed2000

Light quantity controls leaf-cell and chloroplast development in Arabidopsis thaliana wild type and blue-light-perception mutants.

Plants acclimate to changes in light quantity by altering leaf-cell development and the accumulation of chloroplast components, such that light absorption is favoured under limiting illumination, and light utilisation under non-limiting conditions. Previous evidence suggests an involvement of a high-light photosynthetic redox signal in the down-regulation of the accumulation of the light-harvesting complexes of photosystem 11 (Lhcb) and the expression of the Lhcb genes. and of a blue-light signal in the control of leaf development and in the increase in photosynthetic capacity, as affected by the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We examined the internal anatomy of leaves, the ultrastructure of chloroplasts and accumulation of light-harvesting complexes and Rubisco in wild-type Arabidopsis thaliana (L.) Heynh. and in mutants in each of the three known blue-light photoreceptors, cryptochrome 1, cryptochrome 2 and phototropin, as well as a mutant in both cryptochromes. Our results indicate an extensive capacity of the Arabidopsis mesophyll cells to adapt to high light fluence rate with an increase in palisade elongation. Under high light, chloroplasts showed increased starch accumulation and reductions in the amount of granal thylakoids per chloroplast, in the proportion of chlorophyll b relative to chlorophyll a, and in the accumulation of the major Lhcb polypeptides. The responses were similar for all four mutants, with respect to their wild types. The results are consistent with either a complete redundancy in function between cryptochromes and phototropin, or their absence of involvement in the light-quantity responses tested. We observed minimal effects of light quantity on Rubisco accumulation over the range of fluence rates used, and conclude that elongation of palisade mesophyll cells and accumulation of Rubisco are controlled separately. This indicates that light acclimation must be the result of a number of individual elementary responses. Quantitative differences in the acclimatory responses were observed between the Landsberg erecta and Columbia wild-type ecotypes used.

Arabidopsis↗
PubMed2005

Four distinct photoreceptors contribute to light-induced side branch formation in the moss Physcomitrella patens.

Side branch formation in the moss, Physcomitrella patens, has been shown to be light dependent with cryptochrome 1a and 1b (Ppcry1a and Ppcry1b), being the blue light receptors for this response (Imaizumi et al. in Plant Cell 14:373, 2002). In this study, detailed photobiological analyses were performed, which revealed that this response involves multiple photoreceptors including cryptochromes. For light induction of branches, blue light of a fluence rate higher than 6 micromol m(-2) s(-1) for period longer than 3 h is required. The number of branches increased with the increase in fluence rate and in the irradiation period. The number of branches also increased when red light was applied together with the blue light, although red light alone had a very few effect. By partially irradiating a cell, both receptive sites for blue and red light were found to be located around the nucleus. Further, both red and blue light determine the positions of branches being dependent upon the vibration plane of polarized light. Red light control of branch position was nullified by simultaneous far-red light irradiation. A blue light effect on branch position was not found in lines with disrupted phototropin genes. Thus, dichroic phytochrome and phototropin, possibly on the plasma membrane, regulate branch position. These results indicate that at least four distinct photoreceptor systems, namely, cryptochromes and red light receptor around or in the nucleus, dichroic phytochrome and phototropin around the cell periphery, are involved in the light induction of side branches in the moss Physcomitrella patens.

Bryopsida↗
PubMed2003

Making (a) sense of non-visual ocular photoreception.

A subset of intrinsically photosensitive retinal ganglion cells transduce information about ambient lighting conditions to areas of the brain involved in tasks including entrainment of the circadian clock, pupillary light reflexes and melatonin synthesis. The phototransduction system(s) utilized by these cells are unknown. Melanopsin and cryptochromes have been proposed as candidate photopigments for this system. Recent analyses of retinal degenerate mice lacking melanopsin or cryptochromes indicates that outer and inner photoreceptors can both contribute to non-visual photoresponses, and that both melanopsin and cryptochromes play important roles in this process.

Animals↗
PubMed2002

Redox potential: differential roles in dCRY and mCRY1 functions.

Cryptochromes (CRYs) are flavoproteins important for the molecular clocks of animals. The Drosophila cryptochrome (dCRY) is a circadian photoreceptor, whereas mouse cryptochromes (mCRY1 and mCRY2) are essential negative elements of circadian clock transcriptional feedback loops. It has been proposed that reduction/oxidation (redox) reactions are important for dCRY light responsiveness and mCRY1 transcriptional inhibition. We therefore evaluated the role of redox in light-dependent activation of dCRY and in mCRY1 transcriptional inhibition in Drosophila Schneider 2 cells. Using site-directed mutagenesis, three of the four conserved flavin binding residues in dCRY were found to be essential for light responses, whereas three of the four corresponding residues in mCRY1 did not abolish transcriptional responses. Two tryptophan residues in dCRY are critical for its function and are likely involved in an intramolecular redox reaction. The corresponding tryptophan residues do not play a redox-mediated role in mCRY1 function. The data provide a multistep redox model for the light-dependent activities of dCRY and suggest that such a model does not apply to mCRY1 transcriptional responses.

Animals↗
PubMed2002

Light induction of a vertebrate clock gene involves signaling through blue-light receptors and MAP kinases.

The signaling pathways that couple light photoreception to entrainment of the circadian clock have yet to be deciphered. Two prominent groups of candidates for the circadian photoreceptors are opsins (e.g., melanopsin) and blue-light photoreceptors (e.g., cryptochromes). We have previously showed that the zebrafish is an ideal model organism in which to study circadian regulation and light response in peripheral tissues. Here, we used the light-responsive zebrafish cell line Z3 to dissect the response of the clock gene zPer2 to light. We show that the MAPK (mitogen-activated protein kinase) pathway is essential for this response, although other signaling pathways may also play a role. Moreover, action spectrum analyses of zPer2 transcriptional response to monochromatic light demonstrate the involvement of a blue-light photoreceptor. The Cry1b and Cry3 cryptochromes constitute attractive candidates as photoreceptors in this setting. Our results establish a link between blue-light photoreceptors, probably cryptochromes, and the MAPK pathway to elicit light-induced transcriptional activation of clock genes.

Adaptation, Ocular↗
PubMed1999

Seeing the world in red and blue: insight into plant vision and photoreceptors.

Plants see light through multiple photoreceptors, including phytochromes and cryptochromes. Cryptochromes are flavoproteins that participate in many blue-light responses, including phototropism in plants and entrainment of circadian rhythms in plants and animals. A novel flavoprotein, NPH1, is also implicated in plant phototropism. Phytochromes function as serine/threonine kinases whose potential interacting partners include cryptochrome (CRY1 and CRY2).

Animals↗
PubMed2004

Functional analysis of each blue light receptor, cry1, cry2, phot1, and phot2, by using combinatorial multiple mutants in Arabidopsis.

Blue light receptors in Arabidopsis include two types of proteins, cryptochromes and phototropins. Previous studies have suggested that the cryptochromes cry1 and cry2 function mainly in photomorphogenic responses and that the phototropins phot1 and phot2 mainly regulate photo-induced movements. Receptors in the same family have redundant functions, although their responses to the fluence rate of blue light differ. To uncover functions of blue light receptors that may be concealed by their functional redundancy, we conducted analyses of combinatorial multiple mutants of blue light receptors. Comparison of the responses of the quadruple mutant cry1 cry2 phot1 phot2 to blue light with those of related triple mutants revealed that cryptochromes function in blue light-dependent, random hypocotyl-bending and that phototropins function in one photomorphogenic response, cotyledon expansion. Microarray analysis suggested that cry1 and cry2 independently function as key regulators of early blue light-induced genes, whereas phot1 and phot2 play subsidiary roles in transcriptional regulation by blue light.

Arabidopsis↗
PubMed2003

Regulation of photoperiodic flowering by Arabidopsis photoreceptors.

Photoperiodism is a day-length-dependent seasonal change of physiological or developmental activities that is widely found in plants and animals. Photoperiodic flowering in plants is regulated by photosensory receptors including the red/far-red light-receptor phytochromes and the blue/UV-A light-receptor cryptochromes. However, the molecular mechanisms underlying the specific roles of individual photoreceptors have remained poorly understood. Here, we report a study of the day-length-dependent response of cryptochrome 2 (cry2) and phytochrome A (phyA) and their role as day-length sensors in Arabidopsis. The protein abundance of cry2 and phyA showed a diurnal rhythm in plants grown in short-day but not in plants grown in long-day. The short-day-specific diurnal rhythm of cry2 is determined primarily by blue light-dependent cry2 turnover. Consistent with a proposition that cry2 and phyA are the major day-length sensors in Arabidopsis, we show that phyA mediates far-red light promotion of flowering with modes of action similar to that of cry2. Based on these results and a finding that the photoperiodic responsiveness of plants depends on light quality, a model is proposed to explain how individual phytochromes and cryptochromes work together to confer photoperiodic responsiveness in Arabidopsis.

Arabidopsis↗
PubMed1998

Chimeric proteins between cry1 and cry2 Arabidopsis blue light photoreceptors indicate overlapping functions and varying protein stability.

A blue light (cryptochrome) photoreceptor from Arabidopsis, cry1, has been identified recently and shown to mediate a number of blue light-dependent phenotypes. Similar to phytochrome, the cryptochrome photoreceptors are encoded by a gene family of homologous members with considerable amino acid sequence similarity within the N-terminal chromophore binding domain. The two members of the Arabidopsis cryptochrome gene family (CRY1 and CRY2) overlap in function, but their proteins differ in stability: cry2 is rapidly degraded under light fluences (green, blue, and UV) that activate the photoreceptor, but cry1 is not. Here, we demonstrate by overexpression in transgenic plants of cry1 and cry2 fusion constructs that their domains are functionally interchangeable. Hybrid receptor proteins mediate functions similar to cry1 and include inhibition of hypocotyl elongation and blue light-dependent anthocyanin accumulation; differences in activity appear to be correlated with differing protein stability. Because cry2 accumulates to high levels under low-light intensities, it may have greater significance in wild-type plants under conditions when light is limited.

Arabidopsis↗
PubMed2004

Nonvisual photoreception in the chick iris.

The embryonic chicken iris constricts to light ex vivo, but with characteristics atypical of visual phototransduction. The chick iris was most sensitive to short-wavelength light, demonstrating an action spectrum consistent with cryptochrome rather than with opsin pigments. Pupillary responses did not attenuate after saturating light exposure, but showed paradoxical potentiation. Iris photosensitivity was not affected by retinoid depletion or inhibitors of visual phototransduction. Knockdown of cryptochrome expression, but not of melanopsin expression, decreased iris photosensitivity. These data characterize a non-opsin photoreception mechanism in a vertebrate eye and suggest a conserved photoreceptive role for cryptochromes in vertebrates.

Animals↗