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X W Deng

Publications and source records attributed to X W Deng.

At least 37 records · Page 2Linked to original sources
PubMed2000

An Arabidopsis cotyledon-specific albino locus: a possible role in 16S rRNA maturation.

We report here the isolation and characterization of a cotyledon-specific albino locus of Arabidopsis, WHITE COTYLEDONS (WCO). This recessive mutation in the WCO locus, located on the top of Chromosome 1, results in albino cotyledons but green true leaves. An accumulation profile of chlorophylls and ultrastructure of chloroplasts indicate that WCO is necessary for development of functional chloroplasts in cotyledons but is dispensable in true leaves. This was further supported by the fact that the mutants request feeding of sucrose for their survival at the early seedling stage where true leaves have not emerged, but the mutants which have developed true leaves are able to grow autotrophically without sucrose supplementation. The wco mutants accumulate low levels of chloroplast mRNA encoding photosynthesis-related proteins and have a specific defect in 16S rRNA maturation in a cotyledon-specific manner. Although wco mutants exhibited abnormal chloroplasts and chloroplast gene expression in cotyledons, nuclear genes for photosynthetic components are expressed at similar levels to those found in wild-type siblings. This lack of suppression of the nuclear genes is not due to a defect in the signaling of the so-called "plastid factor" to the nucleus since normal suppression of the nuclear genes was observed in response to the photo-oxidative damage due to norflurazon application.

Arabidopsis↗
PubMed1999

The RING finger motif of photomorphogenic repressor COP1 specifically interacts with the RING-H2 motif of a novel Arabidopsis protein.

The constitutive photomorphogenic 1 (COP1) protein of Arabidopsis functions as a molecular switch for the seedling developmental fates: photomorphogenesis under light conditions and skotomorphogenesis in darkness. The COP1 protein contains a cysteine-rich zinc-binding RING finger motif found in diverse groups of regulatory proteins. To understand the role of the COP1 RING finger in mediating protein-protein interaction, we have performed a yeast two-hybrid screen and isolated a novel protein with a RING-H2 motif, a variant type of the RING finger. This protein, designated COP1 Interacting Protein 8 (CIP8), is encoded by a single copy gene and localized to cytosol in a transient assay. In addition to the RING-H2 motif, the predicted protein has a C4 zinc finger, an acidic region, a glycine-rich cluster, and a serine-rich cluster. The COP1 RING finger and the CIP8 RING-H2 domains are sufficient for their interaction with each other both in vitro and in yeast, whereas neither motif displayed significant self-association. Moreover, site-directed mutagenesis studies demonstrated that the expected zinc-binding ligands of the RING finger and RING-H2 fingers are essential for their interaction. Our findings indicate that the RING finger motif, in this case, serves as autonomous protein-protein interaction domain. The allele specific effect of cop1 mutations on the CIP8 protein accumulation in seedlings indicates that its stability in vivo is dependent on the COP1 protein.

Amino Acid Sequence↗
PubMed1999

Evidence for functional conservation of a mammalian homologue of the light-responsive plant protein COP1.

Identified in Arabidopsis as a repressor of light-regulated development, the COP1 (constitutively photomorphogenic 1) protein is characterized by a RING-finger motif and a WD40 repeat domain [1]. The subcellular localization of COP1 is light-dependent. COP1 acts within the nucleus to repress photomorphogenic development, but light inactivates COP1 and diminishes its nuclear abundance [2]. Here, we report the identification of a mammalian COP1 homologue that contains all the structural features present in Arabidopsis COP1 (AtCOP1). When expressed in plant cells, a fusion protein comprising mammalian COP1 and beta-glucuronidase (GUS) responded to light by changing its subcellular localization pattern in a manner similar to AtCOP1. Whereas the mammalian COP1 was unable to rescue the defects of Arabidopsis cop1 mutants, expression of the amino-terminal half of mammalian COP1 in Arabidopsis interfered with endogenous COP1 function, resulting in a hyperphotomorphogenic phenotype. Therefore, the regulatory modules in COP1 proteins that are responsible for the signal-dependent subcellular localization are functionally conserved between higher plants and mammals, suggesting that mammalian COP1 may share a common mode of action with its plant counterpart in regulating development and cellular signaling.

Animals↗
PubMed1999

Characterization of two subunits of Arabidopsis 19S proteasome regulatory complex and its possible interaction with the COP9 complex.

The nuclear localized, multi-subunit COP9 complex (or COP9 signalosome) is a key developmental modulator involved in repression of photomorphogenesis. In an effort to further define the molecular actions of the COP9 complex, a yeast two hybrid interactive screen was undertaken to identify proteins that could directly interact with one subunit of this complex, namely FUS6/COP11. This screen identified one specific interactive protein, AtS9, that is likely the Arabidopsis non-ATPase S9 (subunit 9) of the 19S regulatory complex from the 26S proteasome. AtS9 specifically interacts with FUS6/COP11 via the C-terminal domain of FUS6/COP11, which is distinct from the N-terminal domain necessary for FUS6/COP11 to interact with itself. As anticipated, AtS9 is not a member of the COP9 complex, but tightly associates with an ATPase subunit of the Arabidopsis 19S proteasome regulatory complex, AtS6A. Since all three proteins, FUS6/COP11, AtS9, and AtS6A, are present as complexed forms in vivo, the observed interaction implies that the COP9 complex may directly interact with the 19S regulatory complex of the 26S proteasome or other potential AtS9-containing complex. This notion is consistent with the parallel tissue-specific expression patterns and the similar, predominantly nuclear localization of both the COP9 complex and the AtS9 protein.

Adenosine Triphosphatases↗
PubMed1999

Signalling in light-controlled development.

Plants continuously analyze the nature of environmental light signals using an array of at least eight informational photoreceptors, each with differential functional roles. Molecular and genetic studies are identifying an increasing assembly of potential or established signalling intermediates involved in transducing perceived signals from these photoreceptors to photoresponsive genes. The emerging picture suggests a complex network with both separate and shared early signalling pathway segments which appear to converge to regulate developmentally important genes through a set of master regulators.

Light↗
PubMed1999

Making sense of the COP9 signalosome. A regulatory protein complex conserved from Arabidopsis to human.

The COP9 signalosome, once defined as a repressor complex of light-activated development in Arabidopsis, has recently been found in humans and is probably present in most multicellular organisms. The COP9 signalosome is closely related to the lid sub-complex of the 26S proteasome in structural composition and probably shares a common evolutionary ancestor. A multifaceted role of the COP9 signalosome in cell-signaling processes is hinted at by its associated novel kinase activity, as well as the involvement of its subunits in regulating multiple cell-signaling pathways and cell-cycle progression. The molecular genetic studies in Arabidopsis suggest that the complex functions as part of a highly conserved regulatory network, whose physiological role in animals remains to be determined.

Animals↗
PubMed1999

The role of COP1 in repression of Arabidopsis photomorphogenic development.

Photomorphogenic development in Arabidopsis is regulated by the key repressor COP1, which interacts with specific transcription factors in the nucleus to modulate their activities. In the dark, COP1 accumulates in the nucleus and represses photomorphogenic development. Light diminishes the nuclear accumulation of COP1 and abrogates its repressor activity. A number of cellular components are involved in light-dependent nucleocytoplasmic partitioning of COP1, including the multisubunit COP9 complexes and at least three well-characterized photoreceptors. This review discusses current understanding of the mechanisms of COP1 action.

Arabidopsis↗
PubMed1999

Structural organization and interactions of COP1, a light-regulated developmental switch.

Arabidopsis seedling development follows contrasting patterns depending on ambient light conditions, photomorphogenesis in the light and skotomorphogenesis or etiolation in darkness. COP1 is a limiting or regulatory component in mediating repression of photomorphogenesis in the absence of light. COP1 acts within the nucleus in the dark, directly interacts and regulates specific transcription factors that are required for promoting photomorphogenesis. Light abrogates COP1 action and results in progressive nuclear depletion of COP1 with increasing light stimuli. COP1 contains multiple structural modules, which are responsible for interacting with distinct cellular factors and play specific functional roles. We review the most recent progress in understanding the COP1 action and propose specific models based on the recent studies.

Animals↗
PubMed1999

Protein nucleocytoplasmic transport and its light regulation in plants.

Light exerts a great influence on gene expression, physiology and development pattern in higher plants. Protein factors involved in these processes, such as the photoreceptor, phytochrome B, a key regulatory protein, COP1, and some bZIP transcription factors have been identified and their light-regulated movement between the cytoplasm and the nucleus has been demonstrated. These findings imply that nucleocytoplasmic transport plays a crucial role in light regulation in higher plants. This review summarizes recent investigations into plant nuclear transport systems and specific cases where nucleocytoplasmic transport is subject to light regulation.

Biological Transport↗
PubMed1999

Short communication: the N-terminal fragment of Arabidopsis photomorphogenic repressor COP1 maintains partial function and acts in a concentration-dependent manner.

Arabidopsis seedlings exhibit distinct developmental patterns according to their light environment: photomorphogenesis in the light and etiolation or skotomorphogenesis in darkness. COP1 acts within the nucleus to repress photomorphogenesis in darkness, while light depletes COP1 from nucleus and abrogates this repression. COP1 contains three structural modules: a RING finger followed by a coiled-coil domain, and a WD40 repeat domain at the C-terminus. By introducing various domain deletion mutants of COP1 into cop1 null mutant backgrounds, we show that all three domains are essential for the function of COP1 in vivo. Interestingly, a fragment containing the N-terminal 282 amino acids of COP1 (N282) with both the RING finger and coiled-coil modules is sufficient to rescue the lethality of the cop1 null mutations at low expression level. However, high expression levels of the N282 fragment result in a phenocopy of the cop1 null mutation. The sensitivity of the seedling to levels of N282 could reflect the importance of the abundance of COP1 for the appropriate regulation of photomorphogenic development.

Arabidopsis↗
PubMed1999

Arabidopsis cop8 and fus4 mutations define the same gene that encodes subunit 4 of the COP9 signalosome.

The pleiotropic constitutive photomorphogenic/deetiolated/fusca (cop/det/fus) mutants of Arabidopsis exhibit features of light-grown seedlings when grown in the dark. Cloning and biochemical analysis of COP9 have revealed that it is a component of a multiprotein complex, the COP9 signalosome (previously known as the COP9 complex). Here, we compare the immunoaffinity and the biochemical purification of the COP9 signalosome from cauliflower and confirm its eight-subunit composition. Molecular cloning of subunit 4 of the complex revealed that it is a proteasome-COP9 complex-eIF3 domain protein encoded by a gene that maps to chromosome 5, near the chromosomal location of the cop8 and fus4 mutations. Genetic complementation tests showed that the cop8 and fus4 mutations define the same locus, now designated as COP8. Molecular analysis of the subunit 4-encoding gene in both cop8 and fus4 mutants identified specific molecular lesions, and overexpression of the subunit 4 cDNA in a cop8 mutant background resulted in complete rescue of the mutant phenotype. Thus, we conclude that COP8 encodes subunit 4 of the COP9 signalosome. Examination of possible molecular interactions by using the yeast two-hybrid assay indicated that COP8 is capable of strong self-association as well as interaction with COP9, FUS6/COP11, FUS5, and Arabidopsis JAB1 homolog 1, the latter four proteins being previously defined subunits of the Arabidopsis COP9 signalosome. A comparative sequence analysis indicated that COP8 is highly conserved among multicellular eukaryotes and is also similar to a subunit of the 19S regulatory particle of the 26S proteasome.

Alleles↗
PubMed1998

The Arabidopsis homologue of an eIF3 complex subunit associates with the COP9 complex.

The Arabidopsis COP9 complex is a multi-subunit repressor of photomorphogenesis which is conserved among multicellular organisms. Approximately 12 proteins copurify with the COP9 complex. Seven of these proteins are orthologues of subunits of the recently published mammalian COP9 complex. Four of the proteins show amino acid similarity to various subunits of the COP9 complex, eIF3 complex and 19S cap of the proteasome. We have studied one of these proteins in order to determine if it is a component of the COP9 complex. Arabidopsis p105 is highly similar to the p110 subunit of the human elF3. The p105 gene is induced during photomorphogenesis, and RNA and protein analysis reveal different tissue accumulation patterns. p105 is found in a large protein complex. p105 interacts in yeast with both COP9 and FUS6, two known components of the COP9 complex. Our results indicate that p105 is not a component of the COP9 core complex, though it may interact with components of the complex.

Amino Acid Sequence↗
PubMed1998

Cloning vectors for the expression of green fluorescent protein fusion proteins in transgenic plants.

A series of versatile cloning vectors has been constructed that facilitate the expression of protein fusions to the Aequorea victoria green fluorescent protein (GFP) in plant cells. Amino-terminal- and carboxy-terminal protein fusions have been created and visualized by epifluorescence microscopy, both in transgenic Arabidopsis thaliana and after transient expression in onion epidermal cells. Using tandem dimers and other protein fusions to GFP, we found that the previously described localization of wild-type GFP to the cell nucleus is most likely due to diffusion of GFP across the nuclear envelope rather than to a cryptic nuclear localization signal. A fluorescence-based, quantitative assay for nuclear localization signals is described. In addition, we have employed the previously characterized mutants GFP-S65T and GFP-Y66H in order to allow for the expression of red-shifted and blue fluorescent proteins, respectively, which are suitable for double-labeling studies. Expression of GFP-fusions was controlled by a cauliflower mosaic virus 35S promoter. Using the Arabidopsis COP1 protein as a model, we confirmed a close similarity in the subcellular localization of native COP1 and the GFP-tagged COP1 protein. We demonstrated that COP1 was localized to discrete subnuclear particles and further confirmed that fusion to GFP did not compromise the activity of the wild-type COP1 protein.

Arabidopsis↗
PubMed1998

Functional dissection of Arabidopsis COP1 reveals specific roles of its three structural modules in light control of seedling development.

Arabidopsis COP1 acts as a repressor of photomorphogenesis in darkness, and light stimuli abrogate the repressive ability and nuclear abundance of COP1. COP1 has three known structural modules: an N-terminal RING-finger, followed by a predicted coiled-coil and C-terminal WD-40 repeats. A systematic study was undertaken to dissect the functional roles of these three COP1 domains in light control of Arabidopsis seedling development. Our data suggest that COP1 acts primarily as a homodimer, and probably dimerizes through the coiled-coil domain. The RING-finger and the coiled-coil domains can function independently as light-responsive modules mediating the light-controlled nucleocytoplasmic partitioning of COP1. The C-terminal WD-40 domain functions as an autonomous repressor module since the overexpression of COP1 mutant proteins with intact WD-40 repeats are able to suppress photomorphogenic development. This WD-40 domain-mediated repression can be at least in part accounted for by COP1's direct interaction with and negative regulation of HY5, a bZIP transcription factor that positively regulates photomorphogenesis. However, COP1 self-association is a prerequisite for the observed interaction of the COP1 WD-40 repeats with HY5. This work thus provides a structural basis of COP1 as a molecular switch.

Arabidopsis↗
PubMed1998

Molecular interaction between COP1 and HY5 defines a regulatory switch for light control of Arabidopsis development.

Arabidopsis COP1 acts as a light-inactivable repressor of photomorphogenic development, but its molecular mode of action remains unclear. Here, we show that COP1 negatively regulates HY5, a bZIP protein and a positive regulator of photomorphogenic development. Both in vitro and in vivo assays indicate that COP1 interacts directly and specifically with HY5. The hyperphotomorphogenic phenotype caused by the over-expression of a mutant HY5, which lacks the COP1-interactive domain, supports the regulatory role of HY5-COP1 interaction. Further, HY5 is capable of directly interacting with the CHS1 minimal promoter and is essential for its light activation. We propose that the direct interaction with and regulation of transcription factors by COP1 may represent the molecular mechanism for its control of gene expression and photomorphogenic development.

Acyltransferases↗