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Results for “Light Signal Transduction”

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At least 19 recordsLinked to original sources
PubMed1997

White collar 2, a partner in blue-light signal transduction, controlling expression of light-regulated genes in Neurospora crassa.

A saturating genetic dissection of 'blind' mutants in Neurospora crassa has identified a total of two non-redundant loci (wc-1 and wc-2) each of which is required for blue-light perception/signal transduction. Previously, we demonstrated that WC1 is a putative zinc finger transcription factor able to bind specifically to a light-regulated promoter. Here, we present the cloning and characterization of the wc-2 gene. We demonstrate using mutation analysis and in vitro DNA-binding assays that WC2, the second partner of this light signal transduction system, encodes a functional zinc finger DNA-binding protein with putative PAS dimerization and transcription activation domains. This molecular genetic dissection of the second of two components of this light signal transduction system has enabled us to devise a model whereby WC1 and WC2 are proposed to interact via homologous PAS domains, bind to promoters of light-regulated genes and activate transcription. As such, this study provides the first insight into two co-operating partners in blue-light signal transduction in any organism and describes the molecular tools with which to dissect this enigmatic process.

Amino Acid Sequence↗
PubMed2001

Dissection of the light signal transduction pathways regulating the two early light-induced protein genes in Arabidopsis.

The expression of light-regulated genes in plants is controlled by different classes of photoreceptors that act through a variety of signaling molecules. During photomorphogenesis, the early light-induced protein (Elip) genes are among the first to be induced. To understand the light signal transduction pathways that regulate Elip expression, the two Elip genes, Elip1 and Elip2, in Arabidopsis were studied, taking advantage of the genetic tools available for studying light signaling in Arabidopsis. Using two independent quantitative reverse transcriptase-PCR techniques, we found that red, far-red, and blue lights positively regulate expression of the Elip genes. Phytochrome A and phytochrome B are involved in this signaling. The cryptochrome or phototropin photoreceptors are not required for blue-light induction of either Elip gene, suggesting the involvement of an additional, unidentified, blue-light receptor. Although the COP9 signalosome, a downstream regulator, is involved in dark repression of both Elips, Elip1 and Elip2 show different expression patterns in the dark. The transcription factor HY5 promotes the light induction of Elip1, but not Elip2. A defect in photosystem II activity in greening of hy5 seedlings may result from the loss of Elip1. Heat shock positively controlled Elip1 and Elip2 in a light-independent fashion. This induction is independent of HY5, indicating that heat shock and light activate transcription of the Elip genes through independent pathways.

Arabidopsis↗
PubMed2003

Functional characterization of phytochrome interacting factor 3 in phytochrome-mediated light signal transduction.

Phytochromes regulate various light responses through their interactions with different signaling proteins, such as phytochrome interacting factor 3 (PIF3). However, the physiological functions of PIF3 in light signaling are not yet fully understood. To increase our understanding of these roles, we characterized a T-DNA insertional pif3 mutant and transgenic plants overexpressing the full-length PIF3. Transgenic overexpressing lines displayed longer hypocotyls and smaller cotyledons under red light and reduced cotyledon opening under both red and far-red light, whereas the pif3 mutant showed the opposite phenotypes. The accumulation of anthocyanin and chlorophyll further indicated complicated features of PIF3 function. The accumulation of anthocyanin was increased and the content of chlorophyll was decreased in the overexpression lines. Our data indicate that PIF3 plays complex roles depending on the type of light response and the light conditions.

Arabidopsis↗
PubMed2000

PAT1, a new member of the GRAS family, is involved in phytochrome A signal transduction.

Light signaling via the phytochrome A (phyA) photoreceptor controls basic plant developmental processes including de-etiolation and hypocotyl elongation. We have identified a new Arabidopsis mutant, pat (phytochrome A signal transduction)1-1, which shows strongly reduced responses in continuous far-red light. Physiological and molecular data indicate that this mutant is disrupted at an early step of phyA signal transduction. The PAT1 gene encodes a cytoplasmic protein of 490 amino acids with sequence homologies to the plant-specific GRAS regulatory protein family. In the pat1-1 mutant, a T-DNA insertion introduces a premature stop codon, which likely results in the production of a truncated PAT1 protein of 341 amino acids. The semidominant phenotype of this mutant can be recapitulated by overexpression of an appropriately truncated PAT1 gene in the wild type. The results indicate that the truncated PAT1 protein acts in a dominant-negative fashion to inhibit phyA signaling.

Amino Acid Motifs↗
PubMed2004

Manipulation of light signal transduction as a means of modifying fruit nutritional quality in tomato.

Fruit constitutes a major component of human diets, providing fiber, vitamins, and phytonutrients. Carotenoids are a major class of compounds found in many fruits, providing nutritional benefits as precursors to essential vitamins and as antioxidants. Although recent gene isolation efforts and metabolic engineering have primarily targeted genes involved in carotenoid biosynthesis, factors that regulate flux through the carotenoid pathway remain largely unknown. Characterization of the tomato high-pigment mutations (hp1 and hp2) suggests the manipulation of light signal transduction machinery may be an effective approach toward practical manipulation of plant carotenoids. We demonstrate here that hp1 alleles represent mutations in a tomato UV-DAMAGED DNA-BINDING PROTEIN 1 (DDB1) homolog. We further demonstrate that two tomato light signal transduction genes, LeHY5 and LeCOP1LIKE, are positive and negative regulators of fruit pigmentation, respectively. Down-regulated LeHY5 plants exhibit defects in light responses, including inhibited seedling photomorphogenesis, loss of thylakoid organization, and reduced carotenoid accumulation. In contrast, repression of LeCOP1LIKE expression results in plants with exaggerated photomorphogenesis, dark green leaves, and elevated fruit carotenoid levels. These results suggest genes encoding components of light signal transduction machinery also influence fruit pigmentation and represent genetic tools for manipulation of fruit quality and nutritional value.

Alleles↗
PubMed2001

Blue light adaptation and desensitization of light signal transduction in Neurospora crassa.

The ascomycete Neurospora crassa has the capacity of adapting to a given light quantity, leading to transient blue light responses under continuous light conditions. Here, we present an investigation of this photoadaptation phenomenon. We demonstrated previously that two proteins of the Neurospora blue light signal transduction chain, WC1 and WC2, are subject to light-dependent phosphorylation. WC1 was phosphorylated in parallel with the transient increase in transcript levels of light-regulated genes. Using the light-dependent phosphorylation of WC1 as a marker for an active signalling state of WC1, we show that the transiency of Neurospora blue light responses results from desensitization of the photoreceptor and/or the signalling cascade. Furthermore, a Neurospora mutant was characterized that revealed a specific defect in photoadaptation. In this mutant, the transient expression of light-regulated genes under continuous light, the temporary insensitivity after a light pulse and the capability of differentiating between and adapting to low and high light intensities were abolished. The corresponding protein seems to represent a central component of a negative feedback desensitization mechanism. This negative feedback regulation requires continuous and light-dependent protein de novo biosynthesis.

Adaptation, Physiological↗
PubMed2004

Circadian-controlled basic/helix-loop-helix factor, PIL6, implicated in light-signal transduction in Arabidopsis thaliana.

PHYTOCHROME-INTERACTING FACTOR-LIKE 6 (PIL6) is a member of the large family of basic/helix-loop-helix (bHLH) factors in Arabidopsis thaliana. This circadian-controlled transcription factor was previously suggested to interact with the clock component, TIMING OF CAB EXPRESSION 1 (TOC1). In this study, we isolated a loss-of-function mutant of PIL6, together with a transgenic line aberrantly expressing PIL6 in a manner independent of circadian rhythm. These mutant plants were simultaneously examined with special reference to circadian rhythm and light-signal transduction. The results suggested that PIL6 appears to be not directly involved in the clock function per se. However, the loss-of-function mutant (pil6-1) showed a remarkable phenotype in that it is hypersensitive to red light in seedling de-etiolation. This phenotype was similar to that observed for transgenic lines overexpressing TOC1 (or APRR1). Conversely, transgenic plants overexpressing PIL6 (PIL6-ox) are hyposensitive to red light under the same conditions. This phenotype was very similar to that observed for phyB mutants. The developmental morphologies of PIL6-ox, including the phenotype of early flowering, were also similar to those of phyB mutants. We propose that PIL6 acts as a negative regulator for a red light-mediated morphogenic response (e.g., elongation of hypocotyls in de-etiolation). Taken together, PIL6 might function at an interface between the circadian clock and red light-signal transduction pathways.

Amino Acid Sequence↗
PubMed2005

Structure of a bacterial BLUF photoreceptor: insights into blue light-mediated signal transduction.

Light is an essential environmental factor, and many species have evolved the capability to respond to it. Blue light is perceived through three flavin-containing photoreceptor families: cryptochromes, light-oxygen-voltage, and BLUF (sensor of blue light using flavin adenine dinucleotide, FAD) domain proteins. BLUF domains are present in various proteins from Bacteria and lower Eukarya. They are fully modular and can relay signals to structurally and functionally diverse output units, most of which are implicated in nucleotide metabolism. We present the high resolution crystal structure of the dark resting state of BlrB, a short BLUF domain-containing protein from Rhodobacter sphaeroides. The structure reveals a previously uncharacterized FAD-binding fold. Along with other lines of evidence, it suggests mechanistic aspects for the photocycle that is characterized by a red-shifted absorbance of the flavin. The isoalloxazine ring of FAD binds in a cleft between two helices, whereas the adenine ring points into the solvent. We propose that the adenine ring serves as a hook mediating the interaction with its effector/output domain. The structure suggests a unique photochemical signaling switch in which the absorption of light induces a structural change in the rim surrounding the hook, thereby changing the protein interface between BLUF and the output domain.

Bacterial Proteins↗
PubMed1996

Distinct UV-B and UV-A/blue light signal transduction pathways induce chalcone synthase gene expression in Arabidopsis cells.

UV and blue light control the expression of flavonoid biosynthesis genes in a range of higher plants. To investigate the signal transduction processes involved in the induction of chalcone synthase (CHS) gene expression by UV-B and UV-A/blue light, we examined the effects of specific agonists and inhibitors of known signaling components in mammalian systems in a photomixotrophic Arabidopsis cell suspension culture. CHS expression is induced specifically by these wavelengths in the cell culture, in a manner similar to that in mature Arabidopsis leaf tissue. Both the UV-B and UV-A/blue phototransduction processes involve calcium, although the elevation of cytosolic calcium is insufficient on its own to stimulate CHS expression. The UV-A/blue light induction of CHS expression does not appear to involve calmodulin, whereas the UV-B response does; this difference indicates that the signal transduction pathways are, at least in part, distinct. We provide evidence that both pathways involve reversible protein phosphorylation and require protein synthesis. The UV-B and UV-A/blue light signaling pathways are therefore different from the phytochrome signal transduction pathway regulating CHS expression in other species.

Acyltransferases↗
PubMedDate not supplied

Primary processes during the light-signal transduction of phototropin.

Phototropin is a blue-light photoreceptor in plants that mediates phototropism, chloroplast relocation, stomata opening and leaf expansion. Phototropin molecule has two photoreceptive domains named LOV1 (light-oxygen-voltage) and LOV2 in the N-terminus and a serine/threonine kinase domain in the C-terminus, and acts as a blue light-regulated kinase. Each LOV domain binds a flavin mononucleotide as a chromophore and undergoes unique cyclic reactions upon blue-light absorption that comprises a cysteinyl-flavin adduct formation through a triplet-excited state and a successive adduct break to revert to the initial ground state. The molecular reactions underlying the photocycle are reviewed and one of the probable molecular schemes is presented. Adduct formation alters the secondary protein structure of the LOV domains. This structural change could be transferred to the linker between the kinase domain and involved in the photoregulation of the kinase activity. The structural changes as well as the oligomeric structures seem to differ between LOV1 and LOV2, which may explain the proposed roles of each domain in the photoregulation of the kinase activity. The photoregulation mechanism of phototropin kinase is reviewed and discussed in reference to the regulation mechanism of protein kinase A, which it resembles.

Amino Acid Sequence↗
PubMed1996

Light signal transduction mediated by phytochromes: preliminary studies and possible approaches.

Phytochromes mediate a variety of developmental and growth processes involved in the photomorphogenesis of plants. In this article, we review the current understanding of the structure and function of the photoreceptor, discuss some very preliminary results, and offer speculations and even conjectures that may elicit future studies into the molecular mechanisms of the phytochrome-mediated light signal transduction in plants.

Light↗
PubMed1997

UV and blue light signal transduction in Arabidopsis.

The application of genetic and biochemical approaches in Arabidopsis has generated new insights into the photoreceptors and signal transduction processes that mediate the effects of UV and blue light on gene expression and development. Biochemical studies with an Arabidopsis cell culture have provided information on the signal transduction events that couple UV-B and UV-A/blue light perception to transcription of the chalcone synthase (CHS) gene. Interactions between UV-B and both UV-A and blue light signalling pathways enhance the level of CHS transcription. Mutants which identify negative regulators of CHS transcription in response to UV and blue light have been isolated. The integration of biochemical and genetic approaches will further advance understanding of UV and blue light perception and signal transduction.

Acyltransferases↗
PubMed1997

Characterization of Blue Light Signal Transduction Chains That Control Development and Maintenance of Sexual Competence in Chlamydomonas reinhardtii.

Blue light induces the differentiation of Chlamydomonas reinhardtii pregametes to gametes. The light-induced conversion of pregametes to gametes is protein synthesis dependent and proceeds only after a lag phase. Upon incubation in the dark, gametes lost their mating ability, resulting in dark-inactivated gametes. Reillumination rapidly restored mating competence and this was shown to be independent of protein synthesis. Apparently, differentiation and maintenance of gametic competence are both regulated by light. Whether one or two light-activated signal pathways are involved was investigated using pharmacological compounds that affect signal transduction. Compounds that affected pregamete-to-gamete conversion affected the expression of a gamete-specific gene in a similar fashion. Other drugs affected only dark-inactivated gametes, suggesting that reactivating gametes requires a separate signaling pathway. Combined treatments provided evidence for the consecutive action of a phosphatase and a protein kinase C-like kinase in the light-induced reactivation process.

Journal Article↗
PubMed2002

SPA1, a component of phytochrome A signal transduction, regulates the light signaling current.

Mutations in a component of phytochrome A (phyA)-specific light signal transduction, SPA1, result in enhanced responsiveness of Arabidopsis seedlings to red and far-red light. Here, we have examined the effects of spa1 mutations on the two known modes of phyA function, the high-irradiance responses (HIRs) to continuous irradiation with far-red light and the very-low-fluence responses (VLFRs) to inductive pulses of light that establish only a small proportion of active phyA. spa1 mutants exhibited an enhanced VLFR under hourly pulses of far-red light for hypocotyl growth inhibition, cotyledon unfolding, anthocyanin accumulation, block of greening in subsequent white light and negative regulation of phyB signaling. We provide evidence that the phenotype of spa1 mutants in red light is also caused by an increase in the VLFR. Taken together, our results indicate that light-induced hypocotyl growth inhibition in spa1 mutants is primarily due to a VLFR. While wild-type seedlings required hourly pulses of far-red light to induce a VLFR, infrequent irradiation with far-red pulses (every 12 h) was sufficient to induce a strong VLFR of hypocotyl elongation in spa1 mutants. This shows that the effect of the VLFR was more persistent in spa1 mutants than in the wild type. We, therefore, propose that SPA1 has an important function in reducing the persistence of phyA signaling. spa1 mutations also enhanced the HIRs of anthocyanin accumulation and of phyA-mediated responsivity amplification towards phyB. Thus, our results suggest that spa1 mutations amplify both the phyA-mediated VLFR and the HIR.

Anthocyanins↗
PubMed1993

Evidence against a direct role for inositol phosphate metabolism in the circadian oscillator and the blue-light signal transduction pathway in Neurospora crassa.

The inositol-depletion hypothesis proposes that the effects of Li+ on cellular functions are the result of inhibition by Li+ of the inositol monophosphate phosphatase and subsequent depletion of inositol lipids. This mechanism has been proposed to account for the effects of Li+ on the period of the circadian oscillator. Inositol phosphate metabolism has also been proposed as part of the blue-light signal-transduction pathway through which the phase of the circadian oscillator can be reset by light pulses. Four predictions of these two hypotheses have been tested in the fungus Neurospora crassa and all have been found to fail: (1) inositol supplementation does not reverse the effects of Li+ on the period of the circadian rhythm; (2) inositol depletion of an inositol-requiring mutant does not mimic the effects of Li+; (3) depletion of inositol lipids does not inhibit the response to light; and (4) a phase-resetting pulse of light does not increase the levels of inositol phosphates, including Ins(1,4,5)P3.

Circadian Rhythm↗
PubMed2004

Light signal transduction in higher plants.

Plants utilize several families of photoreceptors to fine-tune growth and development over a large range of environmental conditions. The UV-A/blue light sensing phototropins mediate several light responses enabling optimization of photosynthetic yields. The initial event occurring upon photon capture is a conformational change of the photoreceptor that activates its protein kinase activity. The UV-A/blue light sensing cryptochromes and the red/far-red sensing phytochromes coordinately control seedling establishment, entrainment of the circadian clock, and the transition from vegetative to reproductive growth. In addition, the phytochromes control seed germination and shade-avoidance responses. The molecular mechanisms involved include light-regulated subcellular localization of the photoreceptors, a large reorganization of the transcriptional program, and light-regulated proteolytic degradation of several photoreceptors and signaling components.

Arabidopsis↗