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PubMed2002

Genetics of sensory mechanotransduction.

The molecular mechanisms for the transduction of light and chemical signals in animals are fairly well understood. In contrast, the processes by which the senses of touch, balance, hearing, and proprioception are transduced are still largely unknown. Biochemical approaches to identify transduction components are difficult to use with mechanosensory systems, but genetic approaches are proving more successful. Genetic research in several organisms has demonstrated the importance of cytoskeletal, extracellular, and membrane components for sensory mechanotransduction. In particular, researchers have identified channel proteins in the DEG/ENaC and TRP families that are necessary for signaling in a variety of mechanosensory cells. Proof that these proteins are components of the transduction channel, however, is incomplete.

Animals↗

PubMed2001

Brassinosteroids and gibberellins promote tobacco seed germination by distinct pathways.

Seed germination of Nicotiana tabacum L. cv. Havana 425 is determined by the balance of forces between the growth potential of the embryo and the mechanical restraint of the micropylar endosperm. In contrast to the gibberellin GA4, the brassinosteroid (BR) brassinolide (BL) did not release photodormancy of dark-imbibed photodormant seeds. Brassinolide promoted seedling elongation and germination of non-photodormant seeds, but did not appreciably affect the induction of class I beta-1,3-glucanase (betaGLU I) in the micropylar endosperm. Brassinolide, but not GA4, accelerated endosperm rupture of tobacco seeds imbibed in the light. Brassinolide and GA4 promoted endosperm rupture of dark-imbibed non-photodormant seeds, but only GA4 enhanced betaGLU I induction. Promotion of endosperm rupture by BL was dose-dependent and 0.01 microM BL was most effective. Brassinolide and GA4 promoted abscisic acid (ABA)-inhibited dark-germination of non-photodormant seeds, but only GA4 replaced light in inducing betaGLU I. These results indicate that BRs and GAs promote tobacco seed germination by distinct signal transduction pathways and distinct mechanisms. Gibberellins and light seem to act in a common pathway to release photodormancy, whereas BRs do not release photodormancy. Induction of betaGLU I in the micropylar endosperm and promotion of release of 'coat-enhanced' dormancy seem to be associated with the GA-dependent pathway, but not with BR signalling. It is proposed that BRs promote seed germination by directly enhancing the growth potential of the emerging embryo in a GA- and betaGLU I-independent manner.

Abscisic Acid↗

PubMed2026

Research progress on the regulatory mechanisms of the PSY promoter.

Carotenoids are essential pigments in the plant photosynthetic apparatus, functioning in light harvesting, photoprotection, and signal transduction, and serving as precursors of vital nutrients such as vitamin A. Phytoene synthase (PSY) is the first rate-limiting enzyme in the plant carotenoid biosynthetic pathway, and its transcriptional regulation primarily depends on cis-acting promoter elements, associated transcription factors, and epigenetic status. The PSY promoter region contains core cis-elements as well as multiple light-, hormone-, and stress-responsive elements, which collectively function as key regulatory sites governing spatiotemporal expression. This review systematically summarizes recent advances in PSY promoter regulation by plant hormones (e.g., abscisic acid, ethylene, jasmonic acid), environmental factors (light signaling, temperature, salinity, and drought), and epigenetic mechanisms (DNA methylation, histone modifications, and chromatin remodeling). In addition, the application of transgenic and biotechnological approaches to PSY promoter regulation is further summarized. Including promoter sequence engineering with precise editing of cis-elements and promoter-targeted CRISPR activation/interference (CRISPRa/i) for tunable transcriptional control. Emphasis is placed on how these signals are integrated at the promoter level. Deeper insights into these mechanisms will provide both theoretical foundations and practical strategies for enhancing carotenoid accumulation and stress tolerance in crops through molecular design.

Promoter Regions, Genetic↗

PubMed2001

GUARD CELL SIGNAL TRANSDUCTION.

Guard cells surround stomatal pores in the epidermis of plant leaves and stems. Stomatal pore opening is essential for CO2 influx into leaves for photosynthetic carbon fixation. In exchange, plants lose over 95% of their water via transpiration to the atmosphere. Signal transduction mechanisms in guard cells integrate hormonal stimuli, light signals, water status, CO2, temperature, and other environmental conditions to modulate stomatal apertures for regulation of gas exchange and plant survival under diverse conditions. Stomatal guard cells have become a highly developed model system for characterizing early signal transduction mechanisms in plants and for elucidating how individual signaling mechanisms can interact within a network in a single cell. In this review we focus on recent advances in understanding signal transduction mechanisms in guard cells.

Journal Article↗

PubMed1992

Identification of factors regulating the phosphorylation status of sucrose-phosphate synthase in vivo.

The purpose of this study was to identify the factors that control sucrose-phosphate synthase (SPS)-kinase and SPS-protein phosphatase (SPS-PP) activity in situ, and thereby mediate the activation of SPS by light or mannose. Feeding mannose to excised spinach (Spinacia oleracea) leaves in darkness resulted in a general sequestration of cellular phosphate (as evidenced by accumulation of mannose-6-P and depletion of glucose-6-P [Glc-6-P] and fructose-6-P [Fru-6-P]) and a relatively slow activation of SPS (maximum activation achieved within 90 min). Supplying exogenous inorganic phosphate (Pi) with mannose reduced sequestration of cellular Pi (as evidenced by mannose-6-P accumulation without depletion of hexose-P) and substantially reduced mannose activation of SPS. Thus, depletion of cytoplasmic Pi may be required for SPS activation; accumulation of mannose-6-P alone is clearly not sufficient. It was verified that Glc-6-P, but not mannose-6-P, was an inhibitor of partially purified SPS-kinase, and that Pi was an inhibitor of partially purified SPS-PP. Total extractable activity of SPS-kinase did not vary diurnally, whereas a pronounced light activation of SPS-PP activity was observed. Pretreatment of leaves in the dark with cycloheximide blocked the light activation of SPS-PP (assayed in vitro) and dramatically reduced the rate of SPS activation in situ (in saturating light and carbon dioxide). We conclude that rapid activation of SPS by light involves reduction in cytosolic Pi, an inhibitor of SPS-PP, and light activation of SPS-PP, by a novel mechanism that may involve (directly or indirectly) a protein synthesis step. An increase in cytosolic Glc-6-P, an inhibitor of SPS-kinase, would also favor SPS activation. Thus, the signal transduction pathway mediating the light activation of SPS involves elements of "fine" and "coarse" control.

Journal Article↗

PubMed2000

Light-induced stomatal movement of selected Arabidopsis thaliana mutants.

Various Arabidopsis thaliana mutants with defects in phytohormone signal transduction or the reception of light were analysed with regard to their stomatal response in a red, red/blue light irradiation programme. Stomatal response to light was detected with a customized gas exchange measurement device, optimized for the small model plant. Small transpiration-kinetic variations of the two wild-type lines Columbia (Col) and Landsberg erecta (Ler) were observed. A comparison of the mutant lines to the respective wild type revealed significant differences for the phytochrome A (phyA-103), the abscisic acid insensitive (aba3-2) and the auxin resistant (axr1-3) mutant. Furthermore, the zeaxanthin-less mutant line npq1-2 showed no alterations in stomatal response to light.

Arabidopsis↗

PubMed1999

Insights into eukaryotic multistep phosphorelay signal transduction revealed by the crystal structure of Ypd1p from Saccharomyces cerevisiae.

"Two-component" phosphorelay signal transduction systems constitute a potential target for antibacterial and antifungal agents, since they are found exclusively in prokaryotes and lower eukaryotes (yeast, fungi, slime mold, and plants) but not in mammalian organisms. Saccharomyces cerevisiae Ypd1p, a key intermediate in the osmosensing multistep phosphorelay signal transduction, catalyzes the phosphoryl group transfer between response regulators. Its 1.8 A structure, representing the first example of a eukaryotic phosphorelay protein, contains a four-helix bundle as in the HPt domain of Escherichia coli ArcB sensor kinase. However, Ypd1p has a 44-residue insertion between the last two helices of the helix bundle. The side-chain of His64, the site of phosphorylation, protrudes into the solvent. The structural resemblance between Ypd1p and ArcB HPt domain suggests that both prokaryotes and lower eukaryotes utilize the same basic protein fold for phosphorelay signal transduction. This study sheds light on the best characterized eukaryotic phosphorelay system.

Amino Acid Sequence↗

PubMed2001

Intracellular signaling by the killer immunoglobulin-like receptors and Ly49.

Once thought to be promiscuous killers, it is now known that natural killer (NK) cells possess an elaborate array of receptors that regulate NK cytotoxic and secretory functions upon interaction with target cell MHC class I proteins. These receptors, known as killer cell immunoglobulin-like receptors (KIRs) in humans, and Ly49 receptors in the mouse, have become the focus of intense study in an effort to discern the underlying biology of these large receptor families. These receptor families include both inhibitory and activating receptors. Interrogation of a target expressing KIR ligands leads to coengagement of the inhibitory receptor with as-yet poorly defined activation receptors. Kinases activated during engagement mediate the phosphorylation of the KIR or Ly49 cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). The phosphorylated ITIMs serve as efficient recruitment points for the cytosolic protein tyrosine phosphatases, SHP-1 and SHP-2, resulting in the dephosphorylation of substrates critical for cellular activation. In contrast, some KIRs and Ly49s lack the ITIM and possess a charged residue in their transmembrane domains that mediates interaction with the DAP12 signal transduction chain. DAP12 uses its cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM) to mediate cellular activation. Engagement of a DAP12 coupled KIR or Ly49 results in phosphorylation of DAP12, and other key substrates, including the Syk tryosine kinase, phospholipase C, and c-Cbl. DAP12 activation then leads to the Mapk cascade and ultimately to enhanced degranulation, and production of cytokines and chemokines. Although the context in which inhibitory and activating KIR and Ly49s function is not yet known, the dissection of the activating and inhibitory signal transduction pathways should shed light on their method of integration into the activation sequela of NK cells. Ultimately, this work will lead to concrete understanding of the immunobiology of these seemingly antagonistic receptor systems.

Amino Acid Sequence↗

PubMed2004

Signaling in the mammalian circadian clock: the NO/cGMP pathway.

Mammalian circadian rhythms are generated by a hypothalamic suprachiasmatic nuclei (SCN) clock. Light pulses synchronize body rhythms by inducing phase delays during the early night and phase advances during the late night. Phosphorylation events are known to be involved in circadian phase shifting, both for delays and advances. Pharmacological inhibition of the cGMP-dependent kinase (cGK) or Ca2+/calmodulin-dependent kinase (CaMK), or of neuronal nitric oxide synthase (nNOS) blocks the circadian responses to light in vivo. Light pulses administered during the subjective night, but not during the day, induce rapid phosphorylation of both p-CAMKII and p-nNOS (specifically phosphorylated by CaMKII). CaMKII inhibitors block light-induced nNOS activity and phosphorylation, suggesting a direct pathway between both enzymes. Furthermore, SCN cGMP exhibits diurnal and circadian rhythms with maximal values during the day or subjective day. This variation of cGMP levels appears to be related to temporal changes in phosphodiesterase (PDE) activity and not to guanylyl cyclase (GC) activity. Light pulses increase SCN cGMP levels at circadian time (CT) 18 (when light causes phase advances of rhythms) but not at CT 14 (the time for light-induced phase delays). cGK II is expressed in the hamster SCN and also exhibits circadian changes in its levels, peaking during the day. Light pulses increase cGK activity at CT 18 but not at CT 14. In addition, cGK and GC inhibition by KT-5823 and ODQ significantly attenuated light-induced phase shifts at CT 18. This inhibition did not change c-Fos expression SCN but affected the expression of the clock gene per in the SCN. These results suggest a signal transduction pathway responsible for light-induced phase advances of the circadian clock which could be summarized as follows: Glu-Ca2+-CaMKII-nNOS-GC-cGMP-cGK-->-->clock genes. This pathway offers a signaling window that allows peering into the circadian clock machinery in order to decipher its temporal cogs and wheels.

Animals↗

PubMed2004

A signal transduction pathway model prototype II: Application to Ca2+-calmodulin signaling and myosin light chain phosphorylation.

An agonist-initiated Ca(2+) signaling model for calmodulin (CaM) coupled to the phosphorylation of myosin light chains was created using a computer-assisted simulation environment. Calmodulin buffering was introduced as a module for directing sequestered CaM to myosin light chain kinase (MLCK) through Ca(2+)-dependent release from a buffering protein. Using differing simulation conditions, it was discovered that CaM buffering allowed transient production of more Ca(2+)-CaM-MLCK complex, resulting in elevated myosin light chain phosphorylation compared to nonbuffered control. Second messenger signaling also impacts myosin light chain phosphorylation through the regulation of myosin light chain phosphatase (MLCP). A model for MLCP regulation via its regulatory MYPT1 subunit and interaction of the CPI-17 inhibitor protein was assembled that incorporated several protein kinase subsystems including Rho-kinase, protein kinase C (PKC), and constitutive MYPT1 phosphorylation activities. The effects of the different routes of MLCP regulation depend upon the relative concentrations of MLCP compared to CPI-17, and the specific activities of protein kinases such as Rho and PKC. Phosphorylated CPI-17 (CPI-17P) was found to dynamically control activity during agonist stimulation, with the assumption that inhibition by CPI-17P (resulting from PKC activation) is faster than agonist-induced phosphorylation of MYPT1. Simulation results are in accord with literature measurements of MLCP and CPI-17 phosphorylation states during agonist stimulation, validating the predictive capabilities of the system.

Animals↗

PubMed2005

Visualizing reaction pathways in photoactive yellow protein from nanoseconds to seconds.

Determining 3D intermediate structures during the biological action of proteins in real time under ambient conditions is essential for understanding how proteins function. Here we use time-resolved Laue crystallography to extract short-lived intermediate structures and thereby unveil signal transduction in the blue light photoreceptor photoactive yellow protein (PYP) from Halorhodospira halophila. By analyzing a comprehensive set of Laue data during the PYP photocycle (forty-seven time points from one nanosecond to one second), we track all atoms in PYP during its photocycle and directly observe how absorption of a blue light photon by its p-coumaric acid chromophore triggers a reversible photocycle. We identify a complex chemical mechanism characterized by five distinct structural intermediates. Structural changes at the chromophore in the early, red-shifted intermediates are transduced to the exterior of the protein in the late, blue-shifted intermediates through an initial "volume-conserving" isomerization of the chromophore and the progressive disruption of hydrogen bonds between the chromophore and its surrounding binding pocket. These results yield a comprehensive view of the PYP photocycle when seen in the light of previous biophysical studies on the system.

Bacterial Proteins↗

PubMedDate not supplied

Receptors for the Fc fragment of IgG on natural killer cells.

Natural killer (NK) cells are capable of binding to immune-complexed IgG via CD16-Fc gamma RIIIA molecules on their surface. This interaction activates the NK cell lytic mechanism and induces production of lymphokines by the activated cells. The exact molecular basis for CD16-mediated NK cell activation remains unclear; however, a number of recent studies have provided a framework for future research. It has been shown that CD16 perturbation on NK cells evokes a variety of early signal transduction events in these cells, such as polyphosphatidylinositol hydrolysis, [Ca2+]i increases and protein tyrosine kinase activation. Furthermore, the identification, of CD3-zeta/eta and/or Fc epsilon RI-gamma polypeptides complexed with CD16 in NK cells suggests a signal transduction mechanism analogous to those studied for the T cell receptor and Fc epsilon-receptor complexes. Therefore, research on each of these receptor complexes should now be viewed in light of a potential common signal transduction mechanism. Comparison of the similarities and differences observed should yield valuable insight into the complex network of molecular interactions apparently necessary for CD16-mediated NK cell activation.

Animals↗

PubMedDate not supplied

Caged regulators of signaling pathways.

Although inhibitors can implicate individual protein kinases in specific signal transduction pathways, simple reversible inhibitors are unable to define both the time of initiation and the duration of protein kinase activity. How long must a specific protein kinase remain active in a particular transduction cascade to ensure that the message results in the appropriate cellular response? What is the precise temporal assembly order of individual components of an intracellular signaling complex? What, if any, temporal crosstalk is there between individual members of bisecting signaling pathways? Caged protein kinase inhibitors, as well as caged protein kinases, should serve as useful tools for temporal studies of signal transduction. We have prepared both a caged cyclic AMP-dependent protein kinase and a caged inhibitor of this enzyme. Upon photolysis, the functional activities of both species are dramatically unleashed in vitro. We have also explored both the activation and the inhibition of the cyclic AMP-dependent protein kinase-driven signaling pathway in rat embryo fibroblasts with these caged species via microinjection, and have now demonstrated that the activity of signal transduction pathways can be controlled by light in living cells.

Animals↗

PubMed1996

Calcium and calmodulin are involved in blue light induction of the gsa gene for an early chlorophyll biosynthetic step in Chlamydomonas.

The Chlamydomonas reinhardtii nuclear gene gsa, which encodes the early chlorophyll biosynthetic enzyme glutamate 1-semialdehyde aminotransferase (GSAT), is specifically induced by blue light in cells synchronized in a 12-hr-light and 12-hr-dark regime. Light induction required the presence of a nitrogen source in the incubation medium. Maximal induction also required acetate. However, in the absence of acetate, partial induction occurred when Ca2+ was present in the medium at concentrations of > or = 1 microM. The Ca2+ channel-blocking agents Nd3+ and nifedipine partially inhibited the external Ca(2+)-supported induction of GSAT mRNA but did not inhibit acetate-supported induction. The calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide inhibited both external Ca(2+)-supported and acetate-supported induction. The Ca2+ ionophore A23187 caused a transient induction in the dark. These results suggest that Ca2+ and calmodulin are involved in the signal transduction pathway linking blue light perception to the induction of GSAT mRNA. The electron transport uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited acetate-supported induction of GSAT mRNA but did not inhibit external Ca(2+)-supported induction. It is proposed that in the presence of acetate, an internal pool of Ca2+ can be mobilized as a second message, whereas in the absence of acetate, internal Ca2+ is not available but the requirement for Ca2+ can be partially met by an external Ca2+ source. The mobilization of internal Ca2+ may require energy derived from metabolism of acetate.

Acetates↗

PubMed2000

Identification of cytoskeletal markers for the different microvilli and cell types of the rat vomeronasal sensory epithelium.

The vomeronasal organ (VNO) of the mammal nose is specialized to detect pheromones. The presumed site of the chemosensory signal transduction of pheromones is the vomeronasal brush border of the VNO sensory epithelium, which has been shown to contain two different sets of microvilli: (i) the tall microvilli of supporting cells and (ii) the short microvilli of the chemoreceptive VNO neurons that branch and intermingle with the basal portions of the longer supporting cell microvilli. A key problem when studying the subcellular distribution of possible VNO signal transduction molecules at the light microscope level is the clear discrimination of immunosignals derived from dendritic microvilli of the VNO neurons and surrounding supporting cell structures. In the present study we therefore looked for cytoskeletal marker proteins, that might help to distinguish at the light microscope level between the two sets of microvilli. By immunostaining we found that the VNO dendritic microvilli can be selectively labelled with antibodies to the calcium-sensitive actin filament-bundling protein villin, whereas supporting cell microvilli contain the actin filament cross-linking protein fimbrin, but not villin. Useful cytoplasmic marker molecules for cellular discrimination were cytokeratin 18 for supporting cells and beta-tubulin for dendrites of VNO neurons. A further finding was that the non-sensory epithelium of the rat VNO contains brush cells, a cell type that appears to be involved in certain aspects of chemoreception in the gut. Brush cells or other structures of the vomeronasal brush border did not contain alpha-gustducin.

Actins↗

PubMed2002

His-Asp phosphorelay signal transduction in higher plants: receptors and response regulators for cytokinin signaling in Arabidopsis thaliana.

Bacteria have devised phosphotransfer signaling mechanisms for eliciting a variety of adaptive responses to their environment. These mechanisms are collectively referred to as two-component regulatory systems. Each system generally consists of a sensor protein histidine kinase, which is anchored in the cell membrane, and a cytoplasmic response regulator, whose activity is modulated by the sensor. Most response regulators are transcription factors. In this review, we briefly introduce the established concept on bacterial two-component regulatory systems, using the Agrobacterium VirA-VirG system as an example, and give the evidence for the existence of quite similar systems in higher plants, such as the signal transduction induced by the phytohormone cytokinin. The Arabidopsis CRE1 histidine kinase and its related proteins AHK2 and AHK3 perceive cytokinins in the environment and transduce a signal, presumably through the AHP bridge components that carry the histidine-containing phosphotransfer (HPt) domain, to the ARR1 response regulator that transcriptionally activates genes immediately responsive to cytokinins. In addition, this signal transfer process appears to participate in cross-talk with signaling systems that respond to daylight and another phytohormone, ethylene, through an intracellular pool of several ARR1-like molecular species and the AHP components.

Arabidopsis↗

PubMed1997

Phytochrome-regulated repression of gene expression requires calcium and cGMP.

The plant photoreceptor phytochrome A utilizes three signal transduction pathways, dependent upon calcium and/or cGMP, to activate genes in the light. In this report, we have studied the phytochrome A regulation of a gene that is down-regulated by light, asparagine synthetase (AS1). We show that AS1 is expressed in the dark and repressed in the light. Repression of AS1 in the light is likely controlled by the same calcium/cGMP-dependent pathway that is used to activate other light responses. The use of the same signal transduction pathway for both activating and repressing different responses provides an interesting mechanism for phytochrome action. Using complementary loss- and gain-of-function experiments we have identified a 17 bp cis-element within the AS1 promoter that is both necessary and sufficient for this regulation. This sequence is likely to be the target for a highly conserved phytochrome-generated repressor whose activity is regulated by both calcium and cGMP.

Aspartate-Ammonia Ligase↗

PubMed1995

A synthetic peptide corresponding to the third cytoplasmic loop (residues 533 to 555) of the testicular follicle-stimulating hormone receptor affects signal transduction in rat testis membranes and in intact cultured rat Sertoli cells.

Involvement of the third cytoplasmic (3i) loop (residues 533 to 555) of the rat testicular FSH receptor in the mechanism of FSH signal transduction was examined using light membranes prepared from immature rat testes, monolayer cultures of rat Sertoli cells, and a synthetic peptide strategy. This region of the FSH receptor is structurally related to G protein-activator regions identified in other G protein-coupled receptors. FSHR-(533-555) peptide amide stimulated guanine nucleotide exchange in rat testis light membranes, presumably via its interaction with membrane-associated G protein. The peptide failed to inhibit FSH binding to testis membrane receptors, indicating that the nucleotide exchange effect was not a result of peptide interaction with receptor. When incubated with cultured Sertoli cells from immature rat testes, FSHR-(533-555) peptide amide consistently and significantly inhibited FSH stimulation of cAMP and estradiol biosynthesis, but failed to inhibit forskolin stimulation of each. The peptide effect, therefore, was not due to a direct interaction with adenylyl cyclase. Since FSHR-(533-555) peptide amide did not inhibit FSH binding to membrane receptor, these results imply entry of the peptide into the Sertoli cell, possibly by vesicular internalization or diffusion. Indeed, the inhibitory effects of FSHR-(533-555) peptide amide on FSH-stimulated estradiol biosynthesis were prevented by pretreating Sertoli cells with phenylarsine oxide, an inhibitor of FSH receptor internalization. FSHR-(533-555) was without effect on basal levels of cAMP and estradiol biosynthesis, indicating absence of toxicity at the concentrations tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗