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Results for “Light Signal Transduction”

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At least 73 records · Page 4Linked to original sources
PubMed2005

In planta analysis of protein-protein interactions related to light signaling by bimolecular fluorescence complementation.

The determination of protein-protein interactions is becoming more and more important in the molecular analysis of signal transduction chains. To this purpose the application of a manageable and simple assay in an appropriate biological system is of major concern. Bimolecular fluorescence complementation (BiFC) is a novel method to analyze protein-protein interactions in vivo. The assay is based on the observation that N- and C-terminal subfragments of the yellow-fluorescent protein (YFP) can only reconstitute a functional fluorophore when they are brought into tight contact. Thus, proteins can be fused to the YFP subfragments and the interaction of the fusion proteins can be monitored by epifluorescence microscopy. Pairs of interacting proteins were tested after transient cotransfection in etiolated mustard seedlings, which is a well characterized plant model system for light signal transduction. BiFC could be demonstrated with the F-box protein EID1 (empfindlicher im dunkelroten Licht 1) and the Arabidopsis S-phase kinase-related protein 1 (ASK1). The interaction of both proteins was specific and strictly dependent on the presence of an intact F-box domain. Our studies also demonstrate that etiolated mustard seedlings provide a versatile transient assay system to study light-induced subcellular localization events.

Base Sequence↗
PubMed2003

Reactive oxygen species affect photomorphogenesis in Neurospora crassa.

In Neurospora crassa, several biological phenomena such as the synthesis of carotenoids in the mycelia and polarity of perithecia are regulated by light. We found that a sod-1 mutant, with a defective Cu,Zn-type superoxide dismutase (SOD), showed accelerated light-dependent induction of carotenoid accumulation in the mycelia compared with the wild type. The initial rate of light-induced carotenoid accumulation in the sod-1 mutant was faster than that in the vvd mutant known to accumulate high concentrations. This acceleration was suppressed by treatment with antioxidant reagents. Light-induced transcription of genes involved in carotenoid synthesis, al-1, -2, and -3, was sustained in the sod-1 mutant, whereas it was transient in the wild type. Moreover sod-1 was defective in terms of light-induced polarity of perithecia. By genetic analysis, the enhancement in light-inducible carotenoid synthesis in sod-1 was dependent on the wild type alleles of wc-1 and wc-2. However, the sod-1;vvd double mutant showed additive effects on the carotenoid accumulation in the mycelia. These results suggested that intracellular reactive oxygen species regulated by SOD-1 could affect the light-signal transduction pathway via WC proteins.

Antioxidants↗
PubMed2002

Elongated mesocotyl1, a phytochrome-deficient mutant of maize.

To begin the functional dissection of light signal transduction pathways of maize (Zea mays), we have identified and characterized the light-sensing mutant elm1 (elongated mesocotyl1). Seedlings homozygous for elm1 are pale green, show pronounced elongation of the mesocotyl, and fail to de-etiolate under red or far-red light. Etiolated elm1 mutants contain no spectrally active phytochrome and do not deplete levels of phytochrome A after red-light treatment. High-performance liquid chromatography analyses show that elm1 mutants are unable to convert biliverdin IX alpha to 3Z-phytochromobilin, preventing synthesis of the phytochrome chromophore. Despite the impairment of the phytochrome photoreceptors, elm1 mutants can be grown to maturity in the field. Mature plants retain aspects of the seedling phenotype and flower earlier than wild-type plants under long days. Thus, the elm1 mutant of maize provides the first direct evidence for phytochrome-mediated modulation of flowering time in this agronomically important species.

Biliverdine↗
PubMed2003

Photomorphogenic responses in maize seedling development.

As an emerging maize (Zea mays) seedling senses light, there is a decrease in the rate of mesocotyl elongation, an induction of root growth, and an expansion of leaves. In leaf tissues, mesophyll and bundle sheath cell fate is determined, and the proplastids of each differentiate into the dimorphic chloroplasts typical of each cell type. Although it has been inferred from recent studies in several model plant species that multiple photoreceptor systems mediate this process, surprisingly little is known of light signal transduction in maize. Here, we examine two photomorphogenic responses in maize: inhibition of mesocotyl elongation and C4 photosynthetic differentiation. Through an extensive survey of white, red, far-red, and blue light responses among a diverse collection of germplasm, including a phytochrome-deficient mutant elm1, we show that light response is a highly variable trait in maize. Although all inbreds examined appear to have a functional phytochrome signal transduction pathway, several lines showed reduced sensitivity to blue light. A significant correlation was observed between light response and subpopulation, suggesting that light responsiveness may be a target of artificial selection. An examination of C4 gene expression patterns under various light regimes in the standard W22 inbred and elm1 indicate that cell-specific patterns of C4 gene expression are maintained in fully differentiated tissues independent of light quality. To our knowledge, these findings represent the first comprehensive survey of light response in maize and are discussed in relation to maize breeding strategies.

Base Sequence↗
PubMed1998

The effect of external Ca2+ and Ca(2+)-channel modulators on red-light-induced swelling of protoplasts of Phaseolus radiatus L.

Red-light-induced swelling of the protoplasts isolated from hypocotyl of etiolated mung bean (Phaseolus radiatus L.) was observed only when Ca2+ ions were present in the medium. The optimal CaCl2 concentration was 250 microM. Swelling response declined when Ca2+ was supplied into the medium after red light irradiation. The Ca(2+)-chelator EGTA eliminated the red-light-induced swelling and 45Ca2+ accumulation in the protoplasts. In contrast, A23187, a Ca(2+)-ionophore, could mimic the effect of red light in darkness. These results indicate that Ca2+ may play a role in light signal transduction. In addition, swelling response was prevented by TFP and CPZ (both are CaM antagonists), implying the involvement of CaM in red-light-induced and Ca(2+)-dependent protoplast swelling.

Calcimycin↗
PubMedDate not supplied

[Oxidative stress and cell differentiation in Neurospora crassa].

Environmental stress factors induce oxidative stress in fungi by increasing the intracellular concentrations of reactive oxygen species (ROS). In the mycelium, ROS act as signal molecules needed for cytodifferentiation at certain stages of the development of fungi. Generation of ROS in cells induces the activation of antioxidant protective mechanisms. The purpose of this communication is to analyze the role of ROS in light signal transduction, mediated in Neurospora crassa cells by the White Collar Complex.

Antioxidants↗
PubMed2006

The GRAS protein SCL13 is a positive regulator of phytochrome-dependent red light signaling, but can also modulate phytochrome A responses.

Phytochrome photoreceptors enable plants to perceive divergent light signals leading to adaptive changes in response to differing environmental conditions. However, the mechanism of light signal transduction is not fully understood. Here we report the identification of a new signaling intermediate from Arabidopsis thaliana, Scarecrow-like (SCL)13, which serves as a positive regulator of continuous red light signals downstream of phytochrome B (phyB). SCL13 antisense lines exhibit reduced sensitivity towards red light, but only a distinct subset of phyB-mediated responses is affected, indicating that SCL13 executes its major role in hypocotyl elongation during de-etiolation. Genetic evidence suggests that SCL13 is also needed to modulate phytochrome A (phyA) signal transduction in a phyB-independent way. The SCL13 protein is localized in the cytoplasm, but can also be detected in the nucleus. Overexpression of both a nuclear and cytoplasmic localized SCL13 protein leads to a hypersensitive phenotype under red light indicating that SCL13 is biologically active in both compartments. SCL13 is a member of the plant-specific GRAS protein family, which is involved in various different developmental and signaling pathways. A previously identified phytochrome A signaling intermediate, PAT1, belongs to the same subbranch of GRAS proteins as SCL13. Although both proteins are involved in phytochrome signaling, each is specific for a different light condition and regulates a different subset of responses.

Amino Acid Sequence↗
PubMed2006

Identification of primary target genes of phytochrome signaling. Early transcriptional control during shade avoidance responses in Arabidopsis.

The phytochrome (phy) photoreceptors modulate plant development after perception of light. Upon illumination of etiolated seedlings, phys initiate a transcriptional cascade by directly transducing light signals to the promoters of genes encoding regulators of morphogenesis. In light-grown plants, however, little is known about the transcriptional cascade modulated by phys in response to changes in light. The phy entry points in this cascade are completely unknown. We are particularly interested in the shade avoidance syndrome (SAS). Here we describe a subset of six genes whose expression is rapidly modulated by phys during both deetiolation and SAS in Arabidopsis (Arabidopsis thaliana). Using cycloheximide, we provide evidence that four of these phy rapidly regulated (PAR) genes are direct targets of phy signaling during SAS, revealing these genes as upstream components of the transcriptional cascade. Promoter-beta-glucuronidase fusions confirmed that PAR genes are photoregulated at the transcriptional level. Analysis of gene expression in light signal transduction mutants showed that COP1 and DET1 (but not DET2 or HY5) play a role in modulating PAR expression in response to shade in light-grown seedlings. Moreover, genetic analyses showed that one of the genes identified as a direct target of phy signaling was phy-interacting factor 3-like-1 (PIL1). PIL1 has previously been implicated in SAS in response to transient shade, but we show here that it also plays a key role in response to long-term shade. The action of PIL1 was particularly apparent in a phyB background, suggesting an important negative role for PIL1 under dense vegetation canopies.

Arabidopsis↗
PubMed2002

PIF4, a phytochrome-interacting bHLH factor, functions as a negative regulator of phytochrome B signaling in Arabidopsis.

Plants sense and respond to red and far-red light using the phytochrome (phy) family of photoreceptors. However, the mechanism of light signal transduction is not well defined. Here, we report the identification of a new mutant Arabidopsis locus, srl2 (short under red-light 2), which confers selective hypersensitivity to continuous red, but not far-red, light. This hypersensitivity is eliminated in srl2phyB, but not srl2phyA, double mutants, indicating that this locus functions selectively and negatively in phyB signaling. The SRL2 gene encodes a bHLH factor, designated PIF4 (phytochrome-interacting factor 4), which binds selectively to the biologically active Pfr form of phyB, but has little affinity for phyA. Despite its hypersensitive morphological phenotype, the srl2 mutant displays no perturbation of light-induced expression of marker genes for chloroplast development. These data suggest that PIF4 may function specifically in a branch of the phyB signaling network that regulates a subset of genes involved in cell expansion. Consistent with this proposal, PIF4 localizes to the nucleus and can bind to a G-box DNA sequence motif found in various light-regulated promoters.

Amino Acid Sequence↗
PubMed2004

Signal transduction during light-quality acclimation in cyanobacteria: a model system for understanding phytochrome-response pathways in prokaryotes.

The colorful process of complementary chromatic adaptation (CCA), in which cyanobacteria dramatically alter their pigmentation in response to ambient light color changes, has intrigued scientists for more than a century. Over the past four decades, intensive research on the model organism Fremyella diplosiphon has revealed many details of the photobiology and molecular biology of this process, which includes restructuring of these organism's photosynthetic light-harvesting antennae, called phycobilisomes. This restructuring involves changes in transcription of genes encoding phycobilisome components. These genes have been cloned and their patterns of light-responsive expression characterized. In the past ten years, attention has focused on the signal transduction mechanism(s) through which cyanobacteria sense and respond to changes in ambient light color. Genetic approaches led to the isolation of signal transduction components that control light-color responses in F. diplosiphon. Several of these appear to be within a complex phosphorelay that is in part controlled by a photoreceptor called RcaE, the founding member of a large, novel class of prokaryotic photoreceptors with similarity to both plant phytochrome photoreceptors and sensor histidine kinases. The strong foundation of knowledge provided by years of research on CCA makes this a powerful model system for studying signal transduction systems controlled by prokaryotic phytochromes. In this regard, recent results demonstrate that multiple light sensing systems control this organism's responses to changes in light quality and that large numbers of genes are differentially regulated during this process.

Cyanobacteria↗
PubMed1994

Mutational analyses of light-controlled seedling development in Arabidopsis.

Arabidopsis mutants with decreased responses to light and mutants showing light responses in the dark have both been characterized. Some of the former mutants lack specific photoreceptors, such as the red/far-red light receptor phytochrome A, phytochrome B, or a putative blue light receptor, HY4. These have allowed the assessment of physiological functions of these photoreceptors. The mutants with light responses in the dark include some, such as det1 and cop1, that appear to identify light signal transduction components, and others, such as fus6, that may be less directly related to normal control of light responses. Double mutant studies suggest how the different gene products might interact.

Arabidopsis↗
PubMed2003

A reevaluation of the role of the heterotrimeric G protein in coupling light responses in Arabidopsis.

Previous studies implicated the involvement of a heterotrimeric G protein in red (R) and far-red (FR) light signal transduction, but these studies utilized pharmacological or gain-of-function approaches and, therefore, are indirect tests. Here, we reexamine the role of the single canonical heterotrimeric G protein in R and FR control of hypocotyl growth using a loss-of-function approach. Single- and double-null mutants for the GPA1, AGB1 genes encoding the alpha and beta subunit of the heterotrimeric G protein, respectively, have wild-type sensitivity to R and FR. Ectopic overexpression of wild type and a constitutive active form of the alpha subunit and of the wild-type beta subunit had no effect that can be unequivocally attributed to altered R and FR responsiveness. These results preclude a direct role for the heterotrimeric G complex in R and FR transduction in Arabidopsis leading to growth control in the hypocotyl.

Arabidopsis↗
PubMed2003

DFL2, a new member of the Arabidopsis GH3 gene family, is involved in red light-specific hypocotyl elongation.

A new GH3-related gene, designated DFL2, causes a short hypocotyl phenotype when overexpressed under red and blue light and a long hypocotyl when antisensed under red light conditions. Higher expression of this gene was observed in continuous white, blue and far-red light but the expression level was low in red light and darkness. DFL2 gene expression was induced transiently with red light pulse treatment. DFL2 transgenic plants exhibited a normal root phenotype including primary root elongation and lateral root formation, although primary root elongation was inhibited in antisense transgenic plants only under red light. The adult phenotypes of sense and antisense transgenic plants were not different from that of wild type. DFL2 promoter activity was observed in the hypocotyl. Our results suggest that DFL2 is located downstream of red light signal transduction and determines the degree of hypocotyl elongation.

Arabidopsis Proteins↗
PubMed1997

A cyanobacterial phytochrome two-component light sensory system.

The biliprotein phytochrome regulates plant growth and developmental responses to the ambient light environment through an unknown mechanism. Biochemical analyses demonstrate that phytochrome is an ancient molecule that evolved from a more compact light sensor in cyanobacteria. The cyanobacterial phytochrome Cph1 is a light-regulated histidine kinase that mediates red, far-red reversible phosphorylation of a small response regulator, Rcp1 (response regulator for cyanobacterial phytochrome), encoded by the adjacent gene, thus implicating protein phosphorylation-dephosphorylation in the initial step of light signal transduction by phytochrome.

Amino Acid Sequence↗
PubMed1994

CG-1, a parsley light-induced DNA-binding protein.

A partial cDNA clone (CG-1) encoding a sequence-specific DNA-binding protein (CG-1) was isolated from a parsley (Petroselinum crispum L.) cDNA expression library by a DNA-ligand screening. The nucleotide sequence CGCG is a required motif in this protein's binding site. Interestingly, the mRNA coding for CG-1 accumulated rapidly and transiently in parsley cultured cells after treatment with UV-containing white light. Although the target gene(s) for CG-1 has not been identified, its sequence-specific DNA binding and expression pattern, make CG-1 a possible member of a light signal transduction chain in parsley.

Amino Acid Sequence↗
PubMed2001

A point mutation in nucleoside diphosphate kinase results in a deficient light response for perithecial polarity in Neurospora crassa.

In Neurospora crassa, the phosphorylation of nucleoside diphosphate kinase (NDK)-1 is rapidly enhanced after blue light irradiation. We have investigated the function of NDK-1 in the blue light signal transduction pathway. A mutant called psp (phosphorylation of small protein) shows undetectable phosphorylation of NDK-1 and is defective in light-responsive regulation of perithecial polarity. Sequencing analysis of ndk-1 cDNA by reverse transcription-polymerase chain reaction revealed that proline 72 of ndk-1 was replaced with histidine in psp. The mutation ndk-1(P72H) resulted in accumulation of normal levels of mRNA and of about 25% of NDK-1(P72H) protein compared with that of wild type as determined by Western blot analysis. The ectopic expression of cDNA and introduction of genomic DNA of wild type ndk-1 in psp (ndk-1(P72H)) suppressed the reduction in accumulation and phosphorylation of NDK-1 and the light-insensitive phenotype. These findings demonstrated that the phenotype of psp was caused by the ndk-1(P72H) mutation. Biochemical analysis using recombinant NDK-1 and NDK-1(P72H) indicated that the P72H substitution in NDK-1 was responsible for the decrease in phosphotransfer activities, 5% of autophosphorylation activity, and 2% of V(max) for protein kinase activity phosphorylating myelin basic protein, compared with those of wild type NDK-1, respectively.

Amino Acid Substitution↗
PubMed1993

Regulation of gene expression by light.

The past year has seen significant advances in the biochemical, genetic and molecular dissection of the light signal transduction and developmental pathways that lead to photoregulated gene expression in higher plants. A major part of recent research has focused on the assignment of biological functions to the various photoreceptors, the genetic dissection of the photoreceptor action pathways, and the identification of the cis-acting sequences and trans-acting factors that regulate the downstream light-regulated genes.

Base Sequence↗
PubMed2005

Molecular dissection of the promoter of the light-induced and circadian-controlled APRR9 gene encoding a clock-associated component of Arabidopsis thaliana.

In the model higher plant Arabidopsis thaliana, a number of circadian clock-associated protein components have recently been identified. Among them, a small family of ARABIDOPSIS PSEUDO-RESPONSE REGULATORS (APRR1/TOC1, APRR3, APRR5, APRR7, and APRR9) is interesting because the most probable clock component TIMING OF CAB EXPRESSION 1 (TOC1) belongs to this family. Several lines of evidence have already been accumulated to support the view that not only APRR1/TOC1 but also other APRR family members are crucial for a better understanding of the molecular link between circadian rhythm and light-signal transduction. Among the APRR1/TOC1 family members, the circadian-controlled APRR9 gene is unique in that its expression is rapidly induced by light at the level of transcription. In this study we dissected the regulatory cis-elements of the light-induced and/or circadian-controlled APRR9 promoter by employing not only a mutant plant carrying a T-DNA insertion in the APRR9 promoter, but also a series of APRR9-promoter::LUC (luciferase) reporters that were introduced into an Arabidopsis cultured cell line (T87 cells). Taking the results of these approaches together, we provide several lines of evidence that the APRR9 promoter contains at least two distinctive and separable regulatory cis-elements: an "L element" responsible for the light-induced expression, followed by an "R element" necessary for the fundamental rhythmic expression of APRR9. Furthermore, APRR1/TOC1 was implicated in the L-element-mediated light response of APRR9, directly or indirectly.

Arabidopsis↗