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PubMed1996

Signaling in Soybean Phenylpropanoid Responses (Dissection of Primary, Secondary, and Conditioning Effects of Light, Wounding, and Elicitor Treatments).

The spatial and temporal deployment of plant defense responses involves a complex interplay of signal events, often resulting in superimposition of signaling processes. We have employed a minimal-wound protocol to clearly separate and characterize the specific contributions of light, wounding, and a wall glucan elicitor preparation (PWG) from Phytophthora sojae (Kauf. and Gerde.) to the regulation of phenylpropanoid defense responses in soybean (Glycine max L. [Merr.]) cotyledon tissues. The assay also allowed us to clearly reconstitute responses to combinations of these primary signals and to examine the effects of other pathogenesis-related molecules on the responses in a defined manner. Light specifically triggers accumulation of malonylglucosyl conjugates of the 5-hydroxy-isoflavone, genistein, which is normally found in epidermal cells. PWG selectively induces accumulation of conjugates of the 5-deoxy-isoflavone daidzein, the first committed precursor of the phytoalexin glyceollin. Wounding initiates phenolic polymer deposition, a process greatly potentiated by PWG and light. Whereas glutathione selectively enhances light induction of genistein conjugates, methyl jasmonate enhances both light and PWG-induced isoflavone conjugate accumulations. Wound exudate fully activates the cell's capacity (competency) for the phenolic polymer and glyceollin responses to PWG, whereas glutathione partially restores competency, favoring coumestrol and phenolic polymer responses to PWG. Abscisic acid inhibits all induced phenylpropanoid responses.

Journal Article↗
PubMed1987

Rapid photoperiodic responses in Japanese quail: is daylength measurement based upon a circadian system?

Experimental photoperiods, presented either once only or repeatedly, were used to assess the oscillatory and hourglass properties of the photoperiodic clock in Japanese quail. Gonadectomized quail on 8-hr daylengths respond to a single skeleton photoperiod consisting of two 8-hr light pulses separated by 2 hr of darkness (i.e., LDLD 8:2:8:6) with a marked increase in secretion rate of luteinizing hormone (LH). This response suggests that the second light pulse interacts with a "photoinducible phase" (phi i) lying some 10-16 hr from "dawn" (start of the first light pulse). If, however, groups of quail maintained on 8-hr daylengths are transferred to continuous darkness (DD), and the position of the phi i is sought by a single 8-hr light pulse applied at various times on the first or third day of DD, then an increase in circulating LH is, at best, barely detectable. It would appear that a strongly responsive phi i does not recur rhythmically in DD. Instead, the light pulse apparently acts primarily as a "dawn" signal that triggers a single cycle of photoinducibility, since a second 8-hr light pulse, placed to begin 2 hr after the end of the first, induces a large increase in plasma LH. Similar results are obtained if any single 8-hr light pulse presented to animals held in darkness is preceded, 10 hr earlier, by a short "dawn" light signal. Such dawn signals can be effective when very short; a pulse of only 30 sec can cause a subsequent phi i. The dawn pulse is effective at any circadian phase and leads to a single cycle in photoinducibility. In contrast, a much longer light pulse (perhaps not less than 4 hr) is needed to interact with phi i if significant gonadotropin secretion is to be stimulated. In confirmation of the findings described above, we found that Nanda-Hammer lighting schedules have remarkably little effect in stimulating gonadotropin secretion in gonadectomized quail. There is, for example, a very marked difference between the effectiveness of "resonating" schedules such as LD 6:6, which stimulates a high LH secretion rate since each "inductive" light pulse is preceded by an appropriate "dawn" signal, and a theoretically effective schedule such as LD 6:30, which induces a very small response by comparison. Such schedules (even theoretically noninductive ones) can, however, be made very highly inductive if alternate light pulses are preceded by an appropriately positioned 15-min light pulse to act as "dawn."

Animals↗
PubMed2006

The mouse Clock mutation reduces circadian pacemaker amplitude and enhances efficacy of resetting stimuli and phase-response curve amplitude.

The mouse Clock gene encodes a basic helix-loop-helix-PAS transcription factor, CLOCK, that acts in concert with BMAL1 to form the positive elements of the circadian clock mechanism in mammals. The original Clock mutant allele is a dominant negative (antimorphic) mutation that deletes exon 19 and causes an internal deletion of 51 aa in the C-terminal activation domain of the CLOCK protein. Here we report that heterozygous Clock/+ mice exhibit high-amplitude phase-resetting responses to 6-h light pulses (Type 0 resetting) as compared with wild-type mice that have low amplitude (Type 1) phase resetting. The magnitude and time course of acute light induction in the suprachiasmatic nuclei of the only known light-induced core clock genes, Per1 and Per2, are not affected by the Clock/+ mutation. However, the amplitude of the circadian rhythms of Per gene expression are significantly reduced in Clock homozygous and heterozygous mutants. Rhythms of PER2::LUCIFERASE expression in suprachiasmatic nuclei explant cultures also are reduced in amplitude in Clock heterozygotes. The phase-response curves to changes in culture medium are Type 0 in Clock heterozygotes, but Type 1 in wild types, similar to that seen for light in vivo. The increased efficacy of resetting stimuli and decreased PER expression amplitude can be explained in a unified manner by a model in which the Clock mutation reduces circadian pacemaker amplitude in the suprachiasmatic nuclei.

Animals↗
PubMed2003

Roles for WHITE COLLAR-1 in circadian and general photoperception in Neurospora crassa.

The transcription factors WHITE COLLAR-1 (WC-1) and WHITE COLLAR-2 (WC-2) interact to form a heterodimeric complex (WCC) that is essential for most of the light-mediated processes in Neurospora crassa. WCC also plays a distinct non-light-related role as the transcriptional activator in the FREQUENCY (FRQ)/WCC feedback loop that is central to the N. crassa circadian system. Although an activator role was expected for WC-1, unanticipated phenotypes resulting from some wc-1 alleles prompted a closer examination of an allelic series for WC-1 that has uncovered roles for this central regulator in constant darkness and in response to light. We analyzed the phenotypes of five different wc-1 mutants for expression of FRQ and WC-1 in constant darkness and following light induction. While confirming the absolute requirement of WC-1 for light responses, the data suggest multiple levels of control for light-regulated genes.

Circadian Rhythm↗
PubMed1998

Dim-red-light-induced increase in polar auxin transport in cucumber seedlings. I. Development Of altered capacity, velocity, and response to inhibitors

We have developed and characterized a system to analyze light effects on auxin transport independent of photosynthetic effects. Polar transport of [3H]indole-3-acetic acid through hypocotyl segments from etiolated cucumber (Cucumis sativus L.) seedlings was increased in seedlings grown in dim-red light (DRL) (0.5 &mgr;mol m-2 s-1) relative to seedlings grown in darkness. Both transport velocity and transport intensity (export rate) were increased by at least a factor of 2. Tissue formed in DRL completely acquired the higher transport capacity within 50 h, but tissue already differentiated in darkness acquired only a partial increase in transport capacity within 50 h of DRL, indicating a developmental window for light induction of commitment to changes in auxin transport. This light-induced change probably manifests itself by alteration of function of the auxin efflux carrier, as revealed using specific transport inhibitors. Relative to dark controls, DRL-grown seedlings were differentially less sensitive to two inhibitors of polar auxin transport, N-(naphth-1-yl) phthalamic acid and 2,3,5-triiodobenzoic acid. On the basis of these data, we propose that the auxin efflux carrier is a key target of light regulation during photomorphogenesis.

Journal Article↗
PubMed2000

Expression of psbA genes is regulated at multiple levels in the cyanobacterium Synechococcus sp. PCC 7942.

In cyanobacterium Synechococcus sp. PCC 7942 the photosystem II reaction-center protein D1 is encoded by three psbA genes. The psbAI gene encodes D1:1 protein, the form used for acclimated growth, and psbAII and psbAIII genes encode the stress-induced form, D1:2 protein. Strong light and low temperature have been shown to induce the expression of psbAII/III genes and down-regulate the expression of psbAI gene. Recently, we reported the involvement of reduced thiols in the up-regulation of psbAII/III genes. In this study, we have analyzed the regulation of psbA gene expression in Synechococcus further, at both the transcriptional and post-transcriptional levels. We show that the inhibitors of the photosynthetic electron-transfer chain, which have different effects on the redox state of the plastoquinone (PQ) pool, have similar effect on the transcription of psbA genes. The inhibitors 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) do not cause any changes in psbA gene expression when added under low-light conditions, but dramatically reduce the high-light induction of psbAII/III genes when added upon a high-light shift. Moreover, when the thiol reductant, dithiothreitol, is added to Synechococcus cells together with DCMU concomitant with the high-light shift, no inhibition of psbAII/III gene up-regulation takes place, indicating that the thiol redox state rather than the redox state of the PQ pool regulates psbA gene transcription. We also provide evidence for post-transcriptional regulation of psbA gene expression, particularly, inhibition of translation of psbAI transcripts at high light, and demonstrate that the D1 protein synthesis and degradation processes are coregulated in Synechococcus.

Cyanobacteria↗
PubMed1986

Regulation of genes encoding the large subunit of ribulose-1,5-bisphosphate carboxylase and the photosystem II polypeptides D-1 and D-2 during the cell cycle of Chlamydomonas reinhardtii.

Synthesis of the major chloroplast proteins is temporally regulated in light-dark-synchronized Chlamydomonas cells. We have used cloned chloroplast DNA probes, and in vitro and in vivo protein synthesis to examine the cell cycle regulation of photosystem II polypeptides D-1 and D-2, and the large subunit of ribulose-1,5-bisphosphate carboxylase (RuBPCase LS). Synthesis and accumulation of D-1 and D-2 mRNAs occurs during the first half of the light period (G1), correlating with increasing synthesis of the polypeptides. Rifampicin, added immediately before the light period, inhibited the normal increase in D-1, D-2 polypeptide synthesis. During the dark period D-1, D-2 mRNAs persist at high levels despite reduced rates of mRNA synthesis and translation during this period. Cell-free translation analyses indicate that the D-1 mRNA present during the dark period is efficient at directing synthesis of the D-1 precursor in vitro. We conclude that expression of the psbA (D-1) and psbD (D-2) genes are regulated primarily at the transcriptional level during the light-induction period but at the translational level for the remainder of the cell cycle. Transcripts of the RuBPCase LS gene (rbcL) are also found at high levels during the light and dark periods but, unlike D-1 and D-2, LS mRNA levels do not increase until the last half of the light period and measurable synthesis and accumulation of this mRNA occurs during the dark. Furthermore, induction of LS polypeptide synthesis during the light period is insensitive to rifampicin. We conclude that LS production is regulated primarily at the translational level during the cell cycle.

Cell Cycle↗
PubMed2000

Reciprocal expression of the TNF family receptor herpes virus entry mediator and its ligand LIGHT on activated T cells: LIGHT down-regulates its own receptor.

The TNF receptor (TNFR) family plays a central role in the development of the immune response. Here we describe the reciprocal regulation of the recently identified TNFR superfamily member herpes virus entry mediator (HVEM) (TR2) and its ligand LIGHT (TL4) on T cells following activation and the mechanism of this process. T cell activation resulted in down-regulation of HVEM and up-regulation of LIGHT, which were both more pronounced in CD8(+) than CD4(+) T lymphocytes. The analysis of HVEM and LIGHT mRNA showed an increase in the steady state level of both mRNAs following stimulation. LIGHT, which was present in cytoplasm of resting T cells, was induced both in cytoplasm and at the cell surface. For HVEM, activation resulted in cellular redistribution, with its disappearance from cell surface. HVEM down-regulation did not rely on de novo protein synthesis, in contrast to the partial dependence of LIGHT induction. Matrix metalloproteinase inhibitors did not modify HVEM expression, but did enhance LIGHT accumulation at the cell surface. However, HVEM down-regulation was partially blocked by a neutralizing mAb to LIGHT or an HVEM-Fc fusion protein during activation. As a model, we propose that following stimulation, membrane or secreted LIGHT binds to HVEM and induces receptor down-regulation. Degradation or release of LIGHT by matrix metalloproteinases then contributes to the return to baseline levels for both LIGHT and HVEM. These results reveal a self-regulating ligand/receptor system that contributes to T cell activation through the interaction of T cells with each other and probably with other cells of the immune system.

CD4-Positive T-Lymphocytes↗
PubMed2006

Lightness, filling-in, and the fundamental role of context in visual perception.

Visual perception is defined by the unique spatial interactions that distinguish it from the point-to-point precision of a photometer. Over several decades, Lothar Spillmann has made key observations about the nature of these interactions and the role of context in perception. Our lab has explored the perceptual properties of spatial interactions and more generally the importance of visual context for neuronal responses and perception. Our investigations into the spatiotemporal dynamics of lightness provide insight into underlying mechanisms. For example, backward masking and luminance modulation experiments suggest that the representation of a uniformly luminous object develops first at the borders and, in some manner, the center fills in. The temporal dynamics of lightness induction are also consistent with a filling-in process. There is a slow cutoff temporal frequency above which surround luminance modulation will not elicit perceptual induction of a central area. The larger the central area, the lower the cutoff frequency for induction, perhaps indicating that an edge-based process requires more time to "complete" the larger area. In recordings from primary visual cortex we find that neurons respond in a manner surprisingly consistent with lightness perception and the spatial and temporal properties of induction. For example, the activity of V1 neurons can be modulated by light outside the receptive field and as the modulation rate is increased response modulation falls off more rapidly for large uniform areas than smaller areas. The conclusion we draw from these experiments is that lightness appears to be computed slowly on the basis of edge and context information. A possible role for the spatial interactions is lightness constancy, which is thought to depend on extensive spatial integration. We find not only that V1 responses are strongly context dependent, but that this dependence makes V1 lightness constant on average. The dependence of constancy on surround interactions underscores the fundamental role that context plays in perception. In more recent studies, further support has been found for the importance of context in experiments using natural scene stimuli.

Animals↗
PubMed1995

Light and development regulate the expression of the albino-3 gene in Neurospora crassa.

The albino-3 gene of Neurospora crassa codes for geranylgeranyl pyrophosphate synthase, an enzyme involved in the biosynthesis of carotenoids. The albino-3 locus encodes two overlapping transcription units that give rise to two mRNAs of 2.2 kb (al-3(c)) and 1>6 kb (al-3(m)), with the promoter of the latter residing in the transcribed region of the former. The 1.6-kb transcript was transiently expressed in the mycelium after light induction, while the 2.2-kb mRNA appeared in conidiating cultures only, independently of light. Al-3(c) mRNA was enhanced in the conidiophores and was impaired in mutants blocked at the early stages of conidiation; al-3(c) therefore represents a conidiation-specific transcript. The al-3(c) mRNA level increased upon illumination with blue light and fluctuated according to the circadian cycle.

Base Sequence↗
PubMed2003

VIVID is a flavoprotein and serves as a fungal blue light photoreceptor for photoadaptation.

Blue light regulates many physiological and developmental processes in fungi. Most of the blue light responses in the ascomycete Neurospora crassa are dependent on the two blue light regulatory proteins White Collar (WC)-1 and -2. WC-1 has recently been shown to be the first fungal blue light photoreceptor. In the present study, we characterize the Neurospora protein VIVID. VIVID shows a partial sequence similarity with plant blue light photoreceptors. In addition, we found that VIVID non-covalently binds a flavin chromophore. Upon illumination with blue light, VIVID undergoes a photocycle indicative of the formation of a flavin-cysteinyl adduct. VVD is localized in the cytoplasm and is only present after light induction. A loss-of-function vvd mutant was insensitive to increases in light intensities. Furthermore, mutational analysis of the photoactive cysteine indicated that the formation of a flavin-cysteinyl adduct is essential for VIVID functions in vivo. Our results show that VIVID is a second fungal blue light photoreceptor which enables Neurospora to perceive and respond to daily changes in light intensity.

Amino Acid Sequence↗
PubMed1993

Light-regulated and cell-specific expression of tomato rbcS-gusA and rice rbcS-gusA fusion genes in transgenic rice.

A previously isolated rice (Oryza sativa) rbcS gene was further characterized. This analysis revealed specific sequences in the 5' regulatory region of the rice rbcS gene that are conserved in rbcS genes of other monocotyledonous species. In transgenic rice plants, we examined the expression of the beta-glucuronidase (gusA) reporter gene directed by the 2.8-kb promoter region of the rice rbcS gene. To examine differences in the regulation of monocotyledonous and dicotyledonous rbcS promoters, the activity of a tomato rbcS promoter was also investigated in transgenic rice plants. Our results indicated that both rice and tomato rbcS promoters confer mesophyll-specific expression of the gusA reporter gene in transgenic rice plants and that this expression is induced by light. However, the expression level of the rice rbcS-gusA gene was higher than that of the tomato rbcS-gusA gene, suggesting the presence of quantitative differences in the activity of these particular monocotyledonous and dicotyledonous rbcS promoters in transgenic rice. Histochemical analysis of rbcS-gusA gene expression showed that the observed light induction was only found in mesophyll cells. Furthermore, it was demonstrated that the light regulation of rice rbcS-gusA gene expression was primarily at the level of mRNA accumulation. We show that the rice rbcS gene promoter should be useful for expression of agronomically important genes for genetic engineering of monocotyledonous species.

Amino Acid Sequence↗
PubMed2006

Distinct white collar-1 genes control specific light responses in Mucor circinelloides.

Light regulates many developmental and physiological processes in a large number of organisms. The best-known light response in the fungus Mucor circinelloides is the biosynthesis of beta-carotene. Here, we show that M. circinelloides sporangiophores also respond to light, exhibiting a positive phototropism. Analysis of both responses to different light wavelengths within the visible spectrum demonstrated that phototropism is induced by green and blue light, whereas carotenogenesis is only induced by blue light. The blue regulation of both responses suggests the existence of blue-light photoreceptors in M. circinelloides. Three white collar-1 genes (mcwc-1a, mcwc-1b and mcwc-1c) coding for proteins showing similarity with the WC-1 photoreceptor of Neurospora crassa have been identified. All three contain a LOV (light, oxygen or voltage) domain, similar to that present in fungal and plant blue-light receptors. When knockout mutants for each mcwc-1 gene were generated to characterize gene functions, only mcwc-1c mutants were defective in light induction of carotene biosynthesis, indicating that mcwc-1c is involved in the light transduction pathway that control carotenogenesis. We have also shown that positive phototropism is controlled by the mcwc-1a gene. It seems therefore that mcwc-1a and mcwc-1c genes control different light transduction pathways, although cross-talk between both pathways probably exists because mcwc-1a is involved in the light regulation of mcwc-1c expression.

Amino Acid Sequence↗
PubMed1977

Induction and persistence of pyrimidine dimers in the epidermal DNA of two strains of hairless mice.

The ultraviolet-light induction of DNA damage has been measured in the epidermis of hairless mice with the use of damage-specific endonucleases from Micrococcus luteus. The rates of induction of endonuclease-sensitive sites in HRS/J/Anl and Skh:hairless-1 mice were 6.1 +/- 0.5 X 10(-11) and 6.5 +/- 0.8 X 10(-11)/dalton/J/sq m from a FS40 fluorescent sun lamp (280 to 400 nm), respectively. Enzymatic photoreactivation with yeast photoreactivating enzyme showed that approximately 80% of the endonuclease-sensitive sites were cycloburyl pyrimidine dimers. In both strains of mice the pyrimidine dimers remained in high-molecular-weight DNA for 24 hr after irradiation. These data show that mouse epithelial cells in vivo have little or no capacity for the excision repair of pyrimidine dimers.

Animals↗
PubMed1993

Enhancer activity of light-responsive regulatory elements in the untranslated leader regions of cyanobacterial psbA genes.

Three psbA genes encoding the D1 protein of the photosystem II reaction center are differentially expressed under different light intensities in the cyanobacterium Synechococcus sp. strain PCC 7942. Two of the three psbA genes, psbAII and psbAIII, are induced rapidly when light intensity is increased from 125 x 10(-6) mol.m-2.s-1 to 750 x 10(-6) mol.m-2.s-1. A recombinational cloning vector that carries a transcriptional lacZ reporter gene was used to characterize the controlling elements responsible for light induction. At least three distinct cis elements are present in the regulatory regions of pbsAII and psbAIII: basal promoters, comparable to Escherichia coli sigma 70 promoters in position and sequence, confer constitutive expression of the genes under both low and high light intensities; negative elements upstream of the promoters down-regulate the expression of the corresponding gene; and sequences downstream of the promoters that correspond to the untranslated leader regions of the mRNAs (+1 to +41 in psbAII and +1 to +39 in psbAIII) are responsible for increased expression under high light. When these light-responsive elements were combined with an E. coli promoter (conII) in different positions and orientations, the expression of the lacZ gene was induced 4- to 11-fold. The induction of gene expression under high light by these enhancers was position independent but orientation dependent. When the elements were combined with the conII promoter in the correct orientation, they also conferred a small but reproducible level of light-responsive expression on this E. coli promoter.

Bacterial Proteins↗
PubMed1999

Rapid blue light regulation of a Trichoderma harzianum photolyase gene.

Photolyases and blue light receptors belong to a superfamily of flavoproteins that make use of blue and UVA light either to catalyze DNA repair or to control development. We have isolated a DNA photolyase gene (phr1) from Trichoderma harzianum, a common soil fungus that is of interest as a biocontrol agent against soil-borne plant pathogens and as a model for the study of light-dependent development. The sequence of phr1 is similar to other Class I Type I eukaryotic photolyase genes. Low fluences of blue light rapidly induced phr1 expression both in vegetative mycelia, which lack photoprotective pigments, and, to a greater extent, in conidiophores. Thus, visible light induces the development of pigmented, resistant spores as well as the expression of phr1, perhaps announcing in this way the imminent exposure to the more damaging short wavelengths of sunlight. Light induction of phr1 in non-sporulating mutants shows that a complete sporulation pathway is not required for photoregulation. The light requirements for photoinduction of phr1 were not altered in dimY photoperception mutants. This suggests that photoinduction of sporulation and of photolyase expression is distinct in their photoreceptor system or in the transduction of the blue light signal.

Amino Acid Sequence↗
PubMed1993

Molecular characterization of two cDNAs from Sinapis alba L. expressed specifically at an early stage of tapetum development.

Flower formation in the long-day plant Sinapis alba is strictly dependent on an inductive light treatment. Differential screening of an apex cDNA library prepared 10 days after flower induction against cDNAs from vegetative apices has identified two cDNA clones, pSFD10.35 and pSFD10.44, which represent transcripts expressed transiently between day 10 and day 20 after induction and which disappear before flowers reach maturity. The corresponding full-length cDNAs which were isolated, Satap35 and Satap44, display 86% overall sequence identity. These cDNAs encode polypeptides with predicted molecular weights of 12.7 and 12.4 kDa, and isoelectric points of 10.4 and 7.5, respectively. The N-terminal portions of the open reading frames have characteristics of signal sequences. In situ hybridization reveals that both transcripts are localized exclusively in the tapetal cell layer of the anthers. Maximal expression is observed in flower buds of approximately 1.5 mm length (tetrad stage). Southern blot analysis demonstrates the presence of additional, closely related genes in the Sinapis genome, as well as the occurrence of homologous genes in Arabidopsis thaliana, Brassica napus and Nicotiana tabacum.

Amino Acid Sequence↗
PubMed1998

N-ras mutations are common in melanomas from sun-exposed skin of humans but rare in mucosal membranes or unexposed skin.

Ras mutations, preferentially in codon 61 of the N-ras oncogene, are common in human cutaneous melanomas. In this study, we questioned the association between ras mutations in primary melanomas and sun exposure. DNA was extracted from formalin-fixed primary melanomas: 28 at chronically sun-exposed head and neck areas, 18 at sites subject to intermittent sun exposure, and 28 from unexposed mucosal membranes (vulva/vagina, anus/ rectum, palate). Mutations of both exons of H-, K-, and N-ras genes were examined by polymerase chain reaction/single-strand conformation polymorphism and by direct nucleotide sequencing of the polymerase chain reaction amplified exons. Thirty-two per cent of the head and neck melanomas and 11% of the melanomas from intermittently sun-exposed skin had N-ras codon 61 mutations; comparatively only 7% of the tumors from the unexposed areas had such mutations. One vulvar melanoma had an N-ras codon 12 mutation. No H-ras or K-ras mutations were detected in any sample. The frequency of N-ras exon 2 mutations in melanomas of typically sunbathed skin was compared for the first time with that in melanomas of areas completely protected from sun exposure. The significantly higher frequency (p = 0.04, chi square exact test) of these N-ras mutations on the head and neck demonstrates their UV-light induction in a subset of melanomas explaining one of the molecular effects of UV light in human skin.

Base Sequence↗