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J Chory

Publications and source records attributed to J Chory.

At least 55 records · Page 3Linked to original sources
PubMed1998

Suppressors of an Arabidopsis thaliana phyB mutation identify genes that control light signaling and hypocotyl elongation.

Ambient light controls the development and physiology of plants. The Arabidopsis thaliana photoreceptor phytochrome B (PHYB) regulates developmental light responses at both seedling and adult stages. To identify genes that mediate control of development by light, we screened for suppressors of the long hypocotyl phenotype caused by a phyB mutation. Genetic analyses show that the shy (short hypocotyl) mutations we have isolated fall in several loci. Phenotypes of the mutants suggest that some of the genes identified have functions in control of light responses. Other loci specifically affect cell elongation or expansion.

Arabidopsis↗
PubMed1998

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

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

Arabidopsis↗
PubMed1998

New Arabidopsis cue mutants suggest a close connection between plastid- and phytochrome regulation of nuclear gene expression.

We searched for new components that are involved in the positive regulation of nuclear gene expression by light by extending a screen for Arabidopsis cue (chlorophyll a/b-binding [CAB] protein-underexpressed) mutants (H.-M. Li, K. Culligan, R.A. Dixon, J. Chory [1995] Plant Cell 7: 1599-1610). cue mutants display reduced expression of the CAB3 gene, which encodes light-harvesting chlorophyll protein, the main chloroplast antenna. The new mutants can be divided into (a) phytochrome-deficient mutants (hy1 and phyB), (b) virescent or delayed-greening mutants (cue3, cue6, and cue8), and (c) uniformly pale mutants (cue4 and cue9). For each of the mutants, the reduction in CAB expression correlates with the visible phenotype, defective chloroplast development, and reduced abundance of the light-harvesting chlorophyll protein. Levels of protochlorophyllide oxidoreductase (POR) were reduced to varying degrees in etiolated mutant seedlings. In the dark, whereas the virescent mutants displayed reduced CAB expression and the lowest levels of POR protein, the other mutants expressed CAB and accumulated POR at near wild-type levels. All of the mutants, with the exception of cue6, were compromised in their ability to derepress CAB expression in response to phytochrome activation. Based on these results, we propose that the previously postulated plastid-derived signal is closely involved in the pathway through which phytochrome regulates the expression of nuclear genes encoding plastid proteins.

Arabidopsis↗
PubMed1997

A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction.

Brassinosteroids are a class of growth-promoting regulators that play a key role throughout plant development. Despite their importance, nothing is known of the mechanism of action of these steroid hormones. We describe the identification of 18 Arabidopsis dwarf mutants that are unable to respond to exogenously added brassinosteroid, a phenotype that might be expected for brassinosteroid signaling mutants. All 18 mutations define alleles of a single previously described gene, BRI1. We cloned BRI1 and examined its expression pattern. It encodes a ubiquitously expressed putative receptor kinase. The extracellular domain contains 25 tandem leucine-rich repeats that resemble repeats found in animal hormone receptors, plant disease resistance genes, and genes involved in unknown signaling pathways controlling plant development.

Arabidopsis↗
PubMed1997

Conservation of function between mammalian and plant steroid 5alpha-reductases.

Arabidopsis det2 mutants are small dark-green dwarfs displaying pleiotropic defects in light-regulated development during multiple stages of the plant life cycle. The DET2 gene encodes a protein that shares approximately 40% sequence identity with mammalian steroid 5alpha-reductases and is implicated in the synthesis of a class of plant steroids, the brassinosteroids. Here we show that the DET2 protein, when expressed in human embryonic kidney 293 cells, catalyzes the 5alpha-reduction of several animal steroid substrates and has similar kinetic properties to the mammalian steroid 5alpha-reductase enzymes. Moreover, human steroid 5alpha-reductases expressed in det2 mutant plants can substitute for DET2 in brassinosteroid biosynthesis. These data indicate that DET2 is an ortholog of the mammalian steroid 5alpha-reductases and provide further evidence that brassinosteroids play an essential role in light-regulated plant development. The structural and functional conservation between DET2 and human steroid 5alpha-reductases raise interesting issues concerning the evolutionary origin of the steroid hormone signaling system.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1997

Signaling in plants.

Higher plants are sessile organisms that perceive environmental cues such as light and chemical signals and respond by changing their morphologies. Signaling pathways utilize a complex network of interactions to orchestrate biochemical and physiological responses such as flowering, fruit ripening, germination, photosynthetic regulation, and shoot or root development. In this session, the mechanisms of signaling systems that trigger plant responses to light and to the gaseous hormone, ethylene, were discussed. These signals are first sensed by a receptor and transmitted to the nucleus by a complex network. A signal may be transmitted to the nucleus by any of several systems including GTP binding proteins (G proteins), which change activity upon GTP binding; protein kinase cascades, which sequentially phosphorylate and activate a series of proteins; and membrane ion channels, which change ionic characteristics of the cells. The signal is manifested in the nucleus as a change in the activity of DNA-binding proteins, which are transcription factors that specifically interact and modulate the regulatory regions of genes. Thus, detection of an environmental signal is transmitted through a transduction pathway, and changes in transcription factor activity may coordinate changes in the expression of a portfolio of genes to direct new developmental programs.

Arabidopsis↗
PubMed1997

Extragenic suppressors of the Arabidopsis det1 mutant identify elements of flowering-time and light-response regulatory pathways.

Light regulation of seeding morphogenesis is mediated by photoreceptors that perceive red, far-red, blue and UV light. Photomorphogenetic mutants of Arabidopsis have identified several of the primary photoreceptors, as well as a set of negative regulators of seedling photomorphogenesis, including DET1, that appear to act downstream of the photoreceptors. To study the regulatory context in which DET1 acts to repress photomorphogenesis, we used a simple morphological screen to isolate extragenic mutations in six loci, designated ted (for reversal of the det phenotype), that partially or fully suppress the seeding morphological phenotype of det1-1. Genetic analyses indicate that mutations in the ted4 and ted5 loci identify new alleles of the previously described photomorphogenetic loci hy1 and hy5, respectively. Molecular analyses indicate that the ted mutations partially suppress the dark-grown gene expression phenotype of det1-1, and that the mechanism of suppression does not involve direct remediation of the splicing defect caused by the det1-1 mutation. The ted mutations also partially suppress the light-grown morphological phenotype of mature det1-1 plants, and ted1 and ted2 suppress a daylength insensitivity phenotype of det1. TED1, TED2 and TED3 are newly described genes, whose function appears closely associated with that of DET1. In addition, alleles of ted1 are associated with a moderate late-flowering phenotype, suggesting that TED1 plays a role in the pathways that regulate both seedling morphogenesis and the initiation of flowering.

Alleles↗
PubMed1997

Fluence and wavelength requirements for Arabidopsis CAB gene induction by different phytochromes.

The roles of different phytochromes have been investigated in the photoinduction of several chlorophyll a/b-binding protein genes (CAB) of Arabidopsis thaliana. Etiolated seedlings of the wild type, a phytochrome A (PhyA) null mutant (phyA), a phytochrome B (PhyB) null mutant (phyB), and phyA/phyB double mutant were exposed to monochromatic light to address the questions of the fluence and wavelength requirements for CAB induction by different phytochromes. In the wild type and the phyB mutant, PhyA photoirreversibly induced CAB expression upon irradiation with very-low-fluence light of 350 to 750 nm. In contrast, using the phyA mutant, PhyB photoreversibly induced CAB expression with low-fluence red light. The threshold fluences of red light for PhyA- and PhyB-specific induction were about 10 nmol m-2 and 10 mumol m-2, respectively. In addition, CAB expression was photoreversibly induced with low-fluence red light in the phyA/phyB double mutant, revealing that another phytochrome(s) (PhyX) regulated CAB expression in a manner similar to PhyB. These data suggest that plants utilize different phytochromes to perceive light of varying wave-lengths and fluence, and begin to explain how plants respond so exquisitely to changing light in their environment.

Arabidopsis↗
PubMed1997

Attenuation of phytochrome A and B signaling pathways by the Arabidopsis circadian clock.

In higher plants, environmental cues such as light signals are integrated with circadian clock signals to control precisely the daily rhythms observed for many biological functions. We have used a fusion of the promoter of a chlorophyll a/b binding protein gene, CAB2, with firefly luciferase (cab2::luc) to monitor the detailed kinetics of transcription in response to photoreceptor activation in Arabidopsis. Using this marker in phototransduction and circadian-dysfunctional mutants, we studied how signals from phytochrome and the circadian clock are integrated for the regulation of CAB2 transcription. Results from these mutant studies demonstrate that similar expression features, namely, the acute and circadian responses, are present in both etiolated and green seedlings and that the acute and circadian responses are genetically separable. We also demonstrate that persistent Pfr signaling occurs in red light-pulsed etiolated seedlings, which suggests that the circadian clock antagonizes Pfr-mediated signal transduction. Based on these genetic studies, we propose a model for the regulation of CAB2 transcription in which individual photoreceptors and phototransduction components have been assigned to specific pathways for the regulation of discrete kinetic components of the CAB2 expression pattern.

Arabidopsis↗
PubMed1997

The Arabidopsis deetiolated2 mutant is blocked early in brassinosteroid biosynthesis.

The Arabidopsis DEETIOLATED2 (DET2) gene has been cloned and shown to encode a protein that shares significant sequence identity with mammalian steroid 5 alpha-reductases. Loss of DET2 function causes many defects in Arabidopsis development that can be rescued by the application of brassinolide; therefore, we propose that DET2 encodes a reductase that acts at the first step of the proposed biosynthetic pathway--in the conversion of campesterol to campestanol. Here, we used biochemical measurements and biological assays to determine the precise biochemical defect in det2 mutants. We show that DET2 actually acts at the second step in brassinolide biosynthesis in the 5 alpha-reduction of (24R)-24-methylcholest-4-en-3-one, which is further modified to form campestanol. In feeding experiments using 2H6-labeled campesterol, no significant level of 2H6-labeled campestanol was detected in det2, whereas the wild type accumulated substantial levels. Using gas chromatography-selected ion monitoring analysis, we show that several presumed null alleles of det2 accumulated only 8 to 15% of the wild-type levels of campestanol. Moreover, in det2 mutants, the endogenous levels of (24R)-24-methylcholest-4-en-3-one increased by threefold, whereas the levels of all other measured brassinosteroids accumulated to < 10% of wild-type levels. Exogenously applied biosynthetic intermediates of brassinolide were found to rescue both the dark- and light-grown defects of det2 mutants. Together, these results refine the original proposed pathway for brassinolide and indicate that mutations in DET2 block the second step in brassinosteroid biosynthesis. These results reinforce the utility of combining genetic and biochemical analyses to studies of biosynthetic pathways and strengthen the argument that brassinosteroids play an essential role in Arabidopsis development.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1997

Biochemical characterization of Arabidopsis wild-type and mutant phytochrome B holoproteins.

Although phytochrome B (phyB) plays a particularly important role throughout the life cycle of a plant, it has not been studied in detail at the molecular level due to its low abundance. Here, we report on the expression, assembly with chromophore, and purification of epitope-tagged Arabidopsis phyB. In addition, we have reconstructed two missense mutations, phyB-4 and phyB-101, isolated in long hypocotyl screens. We show that mutant proteins phyB-4 and phyB-101 exhibit altered spectrophotometric and biochemical properties relative to the wild-type protein. In particular, we demonstrate that phyB-101 Pfr exhibits rapid nonphotochemical (dark) reversion to Pr that results in a lower photoequilibrium level of the active Pfr form. We conclude that this occurs in vivo as well because phyB-101 mutants are shown to lack an end-of-day-far-red hypocotyl elongation response that requires a stable Pfr species. We propose that this Pfr instability may be the primary molecular mechanism underlying the phyB-101 mutant phenotype.

Arabidopsis↗
PubMed1997

Light control of plant development.

To grow and develop optimally, all organisms need to perceive and process information from both their biotic and abiotic surroundings. A particularly important environmental cue is light, to which organisms respond in many different ways. Because they are photosynthetic and non-motile, plants need to be especially plastic in response to their light environment. The diverse responses of plants to light require sophisticated sensing of its intensity, direction, duration, and wavelength. The action spectra of light responses provided assays to identify three photoreceptor systems absorbing in the red/far-red, blue/near-ultraviolet, and ultraviolet spectral ranges. Following absorption of light, photoreceptors interact with other signal transduction elements, which eventually leads to many molecular and morphological responses. While a complete signal transduction cascade is not known yet, molecular genetic studies using the model plant Arabidopsis have led to substantial progress in dissecting the signal transduction network. Important gains have been made in determining the function of the photoreceptors, the terminal response pathways, and the intervening signal transduction components.

Cryptochromes↗
PubMed1997

The co-ordination of nuclear and organellar genome expression in eukaryotic cells.

Mitochondria and chloroplasts contain their own genetic complement. Eukaryotic cells must establish mechanisms by which the organellar and nuclear genomes are co-ordinately expressed. In the yeast S. cerevisiae, mitochondrial mutants that have respiratory deficiencies have altered patterns of nuclear gene expression. In strains that are deficient in the mitochondrial isoform of citrate synthase there is an up-regulation of the peroxisomal isoform. There is evidence that the mitochondria send a signal to the nucleus which results in the increased expression of the peroxisomal form of citrate synthase. Oxygen induces the biosynthesis of haem. When yeast are grown in aerobic culture, mitochondrial haem is transduced to the nucleus where it induces the expression of nuclear genes which encode proteins important for cellular respiration. Plant cells in which the chloroplasts have suffered photo-oxidative damage do not express nuclear genes that encode photosynthetic protein. Genetic studies in Arabidopsis have resulted in the characterization of mutants that do express nuclear photosynthetic genes when the development of the chloroplast is inhibited. These mutants will be instrumental in identifying the components of the chloroplast-to-nucleus signal-transduction pathways in plant cells. The identity of the signal that informs the nucleus of the developmental site of the chloroplast is unknown. Chlorophyll precursors, haem and porphyrin are considered candidate signal molecules. Recent studies have implicated that the redox state of the plastoquinone pool in chloroplasts may be involved in regulating nuclear gene expression. These studies have also shown that kinases and phosphatases may participate in relaying signals to the nucleus about the functional state of the chloroplast.

Cell Nucleus↗
PubMed1996

From seed germination to flowering, light controls plant development via the pigment phytochrome.

Plant growth and development are regulated by interactions between the environment and endogenous developmental programs. Of the various environmental factors controlling plant development, light plays an especially important role, in photosynthesis, in seasonal and diurnal time sensing, and as a cue for altering developmental pattern. Recently, several laboratories have devised a variety of genetic screens using Arabidopsis thaliana to dissect the signal transduction pathways of the various photoreceptor systems. Genetic analysis demonstrates that light responses are not simply endpoints of linear signal transduction pathways but are the result of the integration of information from a variety of photoreceptors through a complex network of interacting signaling components. These signaling components include the red/far-red light receptors, phytochromes, at least one blue light receptor, and negative regulatory genes (DET, COP, and FUS) that act downstream from the photoreceptors in the nucleus. In addition, a steroid hormone, brassinolide, also plays a role in light-regulated development and gene expression in Arabidopsis. These molecular and genetic data are allowing us to construct models of the mechanisms by which light controls development and gene expression in Arabidopsis. In the future, this knowledge can be used as a framework for understanding how all land plants respond to changes in their environment.

Germination↗
PubMed1996

A role for brassinosteroids in light-dependent development of Arabidopsis.

Although steroid hormones are important for animal development, the physiological role of plant steroids is unknown. The Arabidopsis DET2 gene encodes a protein that shares significant sequence identity with mammalian steroid 5 alpha-reductases. A mutation of glutamate 204, which is absolutely required for the activity of human steroid reductase, abolishes the in vivo activity of DET2 and leads to defects in light-regulated development that can be ameliorated by application of a plant steroid, brassinolide. Thus, DET2 may encode a reductase in the brassinolide biosynthetic pathway, and brassinosteroids may constitute a distinct class of phytohormones with an important role in light-regulated development of higher plants.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗