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PubMed1995

Expression of an Arabidopsis cryptochrome gene in transgenic tobacco results in hypersensitivity to blue, UV-A, and green light.

The Arabidopsis HY4 gene, required for blue-light-induced inhibition of hypocotyl elongation, encodes a 75-kDa flavoprotein (CRY1) with characteristics of a blue-light photoreceptor. To investigate the mechanism by which this photoreceptor mediates blue-light responses in vivo, we have expressed the Arabidopsis HY4 gene in transgenic tobacco. The transgenic plants exhibited a short-hypocotyl phenotype under blue, UV-A, and green light, whereas they showed no difference from the wild-type plant under red/far-red light or in the dark. This phenotype was found to cosegregate with overexpression of the HY4 transgene and to be fluence dependent. We concluded that the short-hypocotyl phenotype of transgenic tobacco plants was due to hypersensitivity to blue, UV-A, and green light, resulting from over-expression of the photoreceptor. These observations are consistent with the broad action spectrum for responses mediated by this cryptochrome in Arabidopsis and indicate that the machinery for signal, transduction required by the CRY1 protein is conserved among different plant species. Furthermore, the level of these photoresponses is seen to be determined by the cellular concentration of this photoreceptor.

Arabidopsis↗
PubMed2006

Involvement of rice cryptochromes in de-etiolation responses and flowering.

In order to elucidate the function of cryptochromes (cry) in rice, we have characterized all rice CRY genes, including OsCRY1a, OsCRY1b and OsCRY2. Our studies revealed that OsCRY1 genes were mainly expressed in the green plant tissue, while OsCRY2 gene expression was high in the coleoptile, flower and callus. Light treatment affected neither the expression of any of the OsCRY genes nor the stability of their transcripts. However, it was found that Oscry2 protein was negatively regulated by blue light. Moreover, the level of Oscry2 protein also decreased upon red light treatment, and this red light-dependent degradation was shown to be mediated by phytochrome B. Overexpression of OsCRY1 genes resulted in an increased responsiveness to blue light when measuring coleoptile growth inhibition. Moreover, growth of leaf sheaths and blades was also repressed more in OsCRY1 overexpressers than in wild type (WT) under blue light conditions. These results suggest that Oscry1s are responsible for regulating blue light-mediated de-etiolation in rice. In addition, OsCRY2 antisense transgenic rice flowered later than WT under both long-day and short-day conditions, indicating that Oscry2 is involved in the promotion of flowering time in rice.

Cryptochromes↗
PubMed2002

Dual regulation of cryptochrome 1 mRNA expression in chicken retina by light and circadian oscillators.

The localization and regulation of chicken cryptochrome 1 (cCry1) mRNA expression in retina was investigated by laser capture microdissection and quantitative real-time RT-PCR. Laser capture microdissection (LCM) of retinal cell layers showed the highest level of cCry1 expression in the ganglion cell and photoreceptor layers. In both layers, expression was high during the daytime and low at night in subjects exposed to a 12:12 h light:dark cycle. Robust circadian oscillations of cCry1 mRNA levels were observed in constant (24 h day) light, but not in constant darkness, with the highest expression during daytime at zeitgeber time (ZT) 8. Unlike cCry1, circadian rhythms of the melatonin-synthesizing enzyme, arylalkylamine N-acetyltransferase, persisted in constant darkness, suggesting that rhythmic cCry1 expression is not essential for circadian clock function or output. On the second day of constant darkness, when cCry1 expression is arrhythmic, light exposure for 2 h significantly increased retinal cCry1 mRNA levels at ZT 4 and 8, times that cCry1 expression is induced in LD and LL. Similar light exposure ending at ZT 20 had no significant effect. Thus, expression of cCry1 mRNA is regulated dually by light and circadian clocks.

Adaptation, Ocular↗
PubMed2005

Examination of the clock gene Cryptochrome 1 in bipolar disorder: mutational analysis and absence of evidence for linkage or association.

Bipolar disorder is associated with malfunctions of the circadian system, which regulates individual circadian rhythms and which enables the adaptation to a daily 24-h cycle and seasonal change. One of the human circadian clock genes, cryptochrome 1 (Cry1) (located on 12q23-q24.1) was analyzed because of its close correspondence to a linkage hotspot for bipolar disorder. We found no evidence for linkage of 52 bipolar families to two Cry1 flanking microsatellites under several parametric and non-parametric models. In order to employ association for a more sensitive test, 25 affected subjects selected from families with positive LOD scores were screened for mutations by sequencing 9.5% of the Cry1 gene. A total of 16 single nucleotide polymorphisms (SNPs) and a 3 base pair insertion were identified. However, no mutations with probable functional impact were found. These novel SNPs and data on allele frequency and linkage disequilibrium structure will be useful for future association analyses. Nine SNPs have been analyzed in a set of 159 parent proband triads. Linkage disequilibrium analyses using single SNPs and haplotypes showed no association to bipolar disease.Additional, more powerful, studies involving Cry1 and other circadian clock genes need to be tested before an association of circadian abnormalities with bipolar disorder can be excluded.

Base Sequence↗
PubMed2002

Functional properties and regulatory complexity of a minimal RBCS light-responsive unit activated by phytochrome, cryptochrome, and plastid signals.

Light-inducible promoters are able to respond to a wide spectrum of light through multiple photoreceptor systems. Several cis-acting elements have been identified as components of light-responsive promoter elements; however, none of these regulatory elements by itself appears to be sufficient to confer light responsiveness; rather, the combination of at least two elements seems to be required. Using phylogenetic structural analysis, we have identified conserved DNA modular arrays (CMAs) associated with light-responsive promoter regions that have been conserved throughout the evolutionary radiation of angiosperms. Here, we report the functional characterization of CMA5, a native 52-bp fragment of the Nicotiana plumbaginifolia rbcS 8B promoter, which contains an I- and a G-box cis-element. CMA5 behaves as a light-responsive minimal unit capable of activating a heterologous minimal promoter in a phytochrome-, cryptochrome-, and plastid-dependent manner. We also show that CMA5 light induction requires HY5 and that downstream negative regulators COP (constitutive photomorphogenic)/DET (de-etiolated) regulate its activity. Our results show that the simplest light-responsive promoter element from photosynthesis-associated genes described to date is the common target for different signals involved in light regulation. The possible mechanism involved in light-transcriptional regulation and tissue specificity of combinatorial elements units is discussed.

Arabidopsis↗
PubMed2005

Cryptochrome 1 contributes to blue-light sensing in pea.

Cryptochromes are widespread in higher plants but their physiological roles as blue-light photoreceptors have been examined in relatively few species. Screening in a phyA null mutant background has identified several blue-light response mutants in pea (Pisum sativum), including one that carries a substitution of a highly conserved glycine residue in the N-terminal photolyase-homologous domain of the pea CRY1 gene. Analyses of cry1, phyA, and phyB mutants show that all three photoreceptors contribute to seedling photomorphogenesis under high-irradiance blue light, whereas phyA is the main photoreceptor active under low irradiances. Triple phyA phyB cry1 mutants grown under high-irradiance blue light are indistinguishable from dark-grown wild-type plants in length and leaf expansion but show a small residual response to higher-irradiance white light. Monogenic cry1 mutants have little discernable phenotype at the seedling stage, but later in development are more elongated than wild-type plants. In addition, the loss of cry1 moderates the short-internode phenotype of older phyA mutants, suggesting an antagonism between phyA and cry1 under some conditions. Pea cry1 has a small inhibitory effect on flowering under long and short days. However, the phyA cry1 double mutant retains a clear promotion of flowering in response to blue-light photoperiod extensions, indicating a role for one or more additional blue-light photoreceptors in the control of flowering in pea.

Amino Acid Sequence↗
PubMed1998

Interaction of cryptochrome 1, phytochrome, and ion fluxes in blue-light-induced shrinking of Arabidopsis hypocotyl protoplasts.

Protoplasts isolated from red-light-adapted Arabidopsis hypocotyls and incubated under red light exhibited rapid and transient shrinking within a period of 20 min in response to a blue-light pulse and following the onset of continuous blue light. Long-persisting shrinkage was also observed during continuous stimulation. Protoplasts from a hy4 mutant and the phytochrome-deficient phyA/phyB double mutant of Arabidopsis showed little response, whereas those from phyA and phyB mutants showed a partial response. It is concluded that the shrinking response itself is mediated by the HY4 gene product, cryptochrome 1, whereas the blue-light responsiveness is strictly controlled by phytochromes A and B, with a greater contribution by phytochrome B. It is shown further that the far-red-absorbing form of phytochrome (Pfr) was not required during or after, but was required before blue-light perception. Furthermore, a component that directly determines the blue-light responsiveness was generated by Pfr after a lag of 15 min over a 15-min period and decayed with similar kinetics after removal of Pfr by far-red light. The anion-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid prevented the shrinking response. This result, together with those in the literature and the kinetic features of shrinking, suggests that anion channels are activated first, and outward-rectifying cation channels are subsequently activated, resulting in continued net effluxes of Cl- and K+. The postshrinking volume recovery is achieved by K+ and Cl- influxes, with contribution by the proton motive force. External Ca2+ has no role in shrinking and the recovery. The gradual swelling of protoplasts that prevails under background red light is shown to be a phytochrome-mediated response in which phytochrome A contributes more than phytochrome B.

Arabidopsis↗
PubMed1998

Conditional synergism between cryptochrome 1 and phytochrome B is shown by the analysis of phyA, phyB, and hy4 simple, double, and triple mutants in Arabidopsis.

Wild-type or phyA, phyB, or hy4 mutant Arabidopsis seedlings lacking phytochrome A (phyA), phytochrome B (phyB), or cryptochrome 1 (cry1), respectively, and the double and triple mutants were used in combination with blue-light treatments given simultaneously with red or far-red light. We investigated the interaction between phytochromes and cry1 in the control of hypocotyl growth and cotyledon unfolding. Under conditions deficient for cry1 (short exposures to blue light) or phyB (far-red background), these photoreceptors acted synergistically: Under short exposures to blue light (3 h/d) added to a red-light background, cry1 activity required phyB (e.g. the hy4 mutant was taller than the wild type but the phyBhy4 mutant was not taller than the phyB mutant). Under prolonged exposures to blue light (24 h/d) added to a far-red light background, phyB activity required cry1 (e.g. the phyAphyB mutant was taller than the phyA mutant but the phyAphyBhy4 mutant was not taller than the phyAhy4 mutant). Under more favorable light inputs, i.e. prolonged exposures to blue light added to a red-light background, the effects of cry1 and phyB were independent. Thus, the synergism between phyB and cry1 is conditional. The effect of cry1 was not reduced by the phyA mutation under any tested light condition. Under continuous blue light the triple mutant phyAphyBhy4 showed reduced hypocotyl growth inhibition and cotyledon unfolding compared with the phyAphyB mutant. The action of cry1 in the phyAphyB double mutant was higher under the red-light than the far-red-light background, indicating a synergistic interaction between cry1 and phytochromes C, D, or E; however, a residual action of cry1 independent of any phytochrome is likely to occur.

Arabidopsis↗
PubMed1998

Genetic interactions between phytochrome A, phytochrome B, and cryptochrome 1 during Arabidopsis development.

Single, double, and triple null combinations of Arabidopsis mutants lacking the photoreceptors phytochrome (phy) A (phyA-201), phyB (phyB-5), and cryptochrome (cry) 1 (hy4-2.23n) were examined for de-etiolation responses in high-fluence red, far-red, blue, and broad-spectrum white light. Cotyledon unhooking, unfolding, and expansion, hypocotyl growth, and the accumulation of chlorophylls and anthocyanin in 5-d-old seedlings were measured under each light condition and in the dark. phyA was the major photoreceptor/effector for most far-red-light responses, although phyB and cry1 modulated anthocyanin accumulation in a phyA-dependent manner. phyB was the major photoreceptor in red light, although cry1 acted as a phyA/phyB-dependent modulator of chlorophyll accumulation under these conditions. All three photoreceptors contributed to most blue light deetiolation responses, either redundantly or additively; however, phyB acted as a modulator of cotyledon expansion dependent on the presence of cry1. As reported previously, flowering time in long days was promoted by phyA and inhibited by phyB, with each suppressing the other's effect. In addition to the effector/modulator relationships described above, measurements of hypocotyls from blue-light-grown seedlings demonstrated phytochrome activity in blue light and cry1 activity in a phyAphyB mutant background.

Arabidopsis↗
PubMed2005

HYPERSENSITIVE TO RED AND BLUE 1, a ZZ-type zinc finger protein, regulates phytochrome B-mediated red and cryptochrome-mediated blue light responses.

Plant photoreceptors that regulate photomorphogenic development include red/far-red-light-absorbing phytochromes and blue/UV-A-light-absorbing cryptochromes. We have undertaken a genetic screen to identify additional components downstream of the photoreceptors in Arabidopsis thaliana. We identified a short hypocotyl mutant under red and blue light, hypersensitive to red and blue 1 (hrb1). Mutation in HRB1 also enhances the end-of-day far-red light response, inhibits leaf expansion and petiole elongation, and attenuates the expression of CAB3 and CHS. Double mutant analysis indicates that phyB is epistatic to hrb1 under red light, and cry1 cry2 is epistatic to hrb1 under blue light for both hypocotyl growth and light-regulated gene expression responses. HRB1 localizes to the nucleus and belongs to a protein family of Drought induced 19 (Di19). HRB1 and all other family members contain a ZZ-type zinc finger domain, which in other organisms is implicated in protein-protein interactions between dystrophin and calmodulin and between transcriptional adaptors and activators. HRB1 activity is also required for red and blue light-induced expression of PHYTOCHROME INTERACTING FACTOR 4 (PIF4). pif4 shows a very similar hypersensitive response as hrb1 to both red light and blue light and is epistatic to hrb1 in control of light-regulated gene expression responses. Thus, the roles of HRB1 and PIF4 together in regulating both red and blue light responses may represent points where red light signaling and blue light signaling intersect.

Amino Acid Sequence↗
PubMed2005

N-terminal domain-mediated homodimerization is required for photoreceptor activity of Arabidopsis CRYPTOCHROME 1.

Cryptochromes (CRY) are blue light receptors that share sequence similarity with photolyases, flavoproteins that catalyze the repair of UV light-damaged DNA. Transgenic Arabidopsis thaliana seedlings expressing the C-terminal domains of the Arabidopsis CRY fused to beta-glucuronidase (GUS) display a constitutive photomorphogenic (COP) phenotype, indicating that the signaling mechanism of Arabidopsis CRY is mediated through the C-terminal domain. The role of the Arabidopsis CRY N-terminal photolyase-like domain in CRY action remains poorly understood. Here, we report the essential role of the Arabidopsis CRY1 N-terminal domain (CNT1) in the light activation of CRY1 photoreceptor activity. Yeast two-hybrid assay, in vitro binding, in vivo chemical cross-linking, gel filtration, and coimmunoprecipitation studies indicate that CRY1 homodimerizes in a light-independent manner. Mutagenesis and transgenic studies demonstrate that CNT1-mediated dimerization is required for light activation of the C-terminal domain of CRY1 (CCT1). Transgenic data and native gel electrophoresis studies suggest that multimerization of GUS is both responsible and required for mediating a COP phenotype on fusion to CCT1. These results indicate that the properties of the GUS multimer are analogous to those of the light-modified CNT1 dimer. Irradiation with blue light modifies the properties of the CNT1 dimer, resulting in a change in CCT1, activating CCT1, and eventually triggering the CRY1 signaling pathway.

Arabidopsis↗
PubMed2006

Evidence for a putative antennal clock in Mamestra brassicae: molecular cloning and characterization of two clock genes--period and cryptochrome-- in antennae.

Circadian rhythms are generated by endogenous circadian clocks, organized in central and peripheral clocks. An antennal peripheral clock has been demonstrated to be necessary and sufficient to generate Drosophila olfactory rhythms in response to food odours. As moth pheromonal communication has been demonstrated to follow daily rhythms, we thus investigated the occurence of a putative antennal clock in the noctuid Mamestra brassicae. From moth antennae, we isolated two full-length cDNAs encoding clock genes, period and cryptochrome, which appeared to be expressed throughout the body. In the antennae, expression of both transcripts was restricted to cells that likely represent olfactory sensory neurones. Our results suggest the occurence of a putative antennal clock that could participate in the pheromonal communication rhythms observed in vivo.

Amino Acid Sequence↗
PubMed1999

Light-dependent sequestration of TIMELESS by CRYPTOCHROME.

Most organisms have circadian clocks consisting of negative feedback loops of gene regulation that facilitate adaptation to cycles of light and darkness. In this study, CRYPTOCHROME (CRY), a protein involved in circadian photoperception in Drosophila, is shown to block the function of PERIOD/TIMELESS (PER/TIM) heterodimeric complexes in a light-dependent fashion. TIM degradation does not occur under these conditions; thus, TIM degradation is uncoupled from abrogation of its function by light. CRY and TIM are part of the same complex and directly interact in yeast in a light-dependent fashion. PER/TIM and CRY influence the subcellular distribution of these protein complexes, which reside primarily in the nucleus after the perception of a light signal. Thus, CRY acts as a circadian photoreceptor by directly interacting with core components of the circadian clock.

Animals↗
PubMed2007

Structure/function analysis of Xenopus cryptochromes 1 and 2 reveals differential nuclear localization mechanisms and functional domains important for interaction with and repression of CLOCK-BMAL1.

Circadian rhythms control the temporal arrangement of molecular, physiological, and behavioral processes within an organism and also synchronize these processes with the external environment. A cell autonomous molecular oscillator, consisting of interlocking transcriptional/translational feedback loops, drives the approximately 24-hour duration of these rhythms. The cryptochrome protein (CRY) plays a central part in the negative feedback loop of the molecular clock by translocating to the nucleus and repressing CLOCK and BMAL1, two transcription factors that comprise the positive elements in this cycle. In order to gain insight into the inner workings of this feedback loop, we investigated the structure/function relationships of Xenopus laevis CRY1 (xCRY1) and xCRY2 in cultured cells. The C-terminal tails of both xCRY1 and xCRY2 are sufficient for their nuclear localization but achieve it by different mechanisms. Through the generation and characterization of xCRY/photolyase chimeras, we found that the second half of the photolyase homology region (PHR) of CRY is important for repression through facilitating interaction with BMAL1. Characterization of these functional domains in CRYs will help us to better understand the mechanism of the known roles of CRYs and to elucidate new intricacies of the molecular clock.

ARNTL Transcription Factors↗
PubMed2001

Photic signaling by cryptochrome in the Drosophila circadian system.

Oscillations of the period (per) and timeless (tim) gene products are an integral part of the feedback loop that underlies circadian behavioral rhythms in Drosophila melanogaster. Resetting this loop in response to light requires the putative circadian photoreceptor cryptochrome (CRY). We dissected the early events in photic resetting by determining the mechanisms underlying the CRY response to light and by investigating the relationship between CRY and the light-induced ubiquitination of the TIM protein. In response to light, CRY is degraded by the proteasome through a mechanism that requires electron transport. Various CRY mutant proteins are not degraded, and this suggests that an intramolecular conversion is required for this light response. Light-induced TIM ubiquitination precedes CRY degradation and is increased when electron transport is blocked. Thus, inhibition of electron transport may "lock" CRY in an active state by preventing signaling required either to degrade CRY or to convert it to an inactive form. High levels of CRY block TIM ubiquitination, suggesting a mechanism by which light-driven changes in CRY could control TIM ubiquitination.

Animals↗
PubMed2003

Expression of the blue-light receptor cryptochrome in the human retina.

PURPOSE: To analyze the patterns of expression of the cryptochromes, CRY1 and CRY2, in the human retina and to correlate expression of these putative blue-light receptors with nonvisual photoreceptor localization. METHODS: CRY1 and CRY2 mRNA expression was analyzed in 4-mm diameter punches of macula and midperipheral human retina by quantitative RT-PCR. CRY2 protein expression was examined by immunohistochemistry in cross sections of human retina, and its subcellular localization was determined by immunoblot analysis of fractionated human retinal extracts. RESULTS: CRY2 mRNA was 11 times more abundant than CRY1 throughout adult human retina. CRY2 immunoreactivity was detected in most cells in the ganglion cell layer (GCL) and in a subset of cells in the inner nuclear layer (INL) in both the macula and periphery. Immunoperoxidase staining further revealed that CRY2 was localized throughout the cytoplasm of cells in the GCL as well as within nuclei. This intracellular localization of CRY2 was confirmed by immunoblot analysis of fractionated human retinal extracts. CONCLUSIONS: Photopigments governing circadian photoreception have been localized to the inner retina. The relative abundance of CRY2 transcripts, coupled with CRY2 localization to the inner retina, supports a photoreceptive role for CRY2 in human retina. Furthermore, the discovery that CRY2 is also localized within the cytoplasm of some cells in the GCL, suggests it may perform a function separate from its known nuclear role in the transcriptional feedback loop underlying the molecular circadian clock.

Adult↗
PubMed2001

Resetting of the circadian clock by phytochromes and cryptochromes in Arabidopsis.

The authors sought to investigate the role of phytochromes A and B (phyA and phyB) and cryptochromes 1 and 2 (cryl and cry2) in the synchronization of the leaf position rhythm in Arabidopsis thaliana. The seedlings were transferred from white light-dark cycles to free-running conditions with or without exposure to a light treatment during the final hours of the last dark period. The phase advance caused by a far-red light treatment was absent in the phyA mutant, deficient in the fhy1 and fhy3 mutants involved in phyA signaling, and normal in the cryl and cryl cry2 mutants. The phase shift caused by blue light was normal in the cry2 mutant; reduced in the phyA, cryl, phyA cry1, and cry1 cry2 mutants; and abolished in the phyA cryl cry2 triple mutant. The phase shift caused by red light was partially retained by the phyA phyB double mutant. The authors conclude that cryl and cry2 participate as photoreceptors in the blue light input to the clock but are not required for the phyA-mediated effects on the phase of the circadian rhythm of leaf position. The signaling proteins FHY1 and FHY3 are shared by phyA-mediated photomorphogenesis and phyA input to the clock.

Arabidopsis↗
PubMed2002

Molecular cloning and circadian regulation of cryptochrome genes in Japanese quail (Coturnix coturnix japonica).

The circadian system is thought to have three components: input, pacemaker (internal clock), and output. Cryptochromes (Cry) are important clock genes, and recent findings indicate that these genes not only act as circadian photoreceptors but are also essential components in the negative feedback of the circadian system. As a first step toward understanding the avian circadian system, the authors tried to clone Japanese quail homologs of mammalian Crys and analyze their expression patterns in different circumstances. Partial cDNAs of qCry1 and qCry2, which are homologs of mammalian Cry1 and Cry2, respectively, were obtained and their gene expressions were analyzed. Both qCry1 and qCry2 mRNAs were present in all the tissues examined. The oscillation patterns of the qCry1 transcripts were tissue specific and generally showed robust changes between daytime and nighttime; except for lung and testis tissues (which showed no detectable changes between daytime and nighttime), daytime levels were higher in all of the tissues examined. This rapid oscillation in qCry1 persisted through constant darkness or constant illumination, indicating that an endogenous clock controls these changes. In contrast, the expression of qCry2 did not oscillate in any tissue examined. In addition, in tissues of the pineal gland and eye, unexpected light exposure in the dark period was able to block the decrease in qCry1 transcripts or induce its expression. These findings, in conjunction with the established roles of CRYs in other species, led the authors to propose that in the circadian system, qCRYs may play important roles similar to the known roles of CRYs of other species, such as acting as circadian photoreceptors and as components of the circadian system.

Amino Acid Sequence↗