Disease relevance of COP1

• By analyzing the COP1 protein expressed in Escherichia coli, we demonstrate here that each COP1 molecule can bind up to two zinc atoms [1].
• Expression of 35S-HFR1(DeltaN) in wild-type plants confers greater hypersensitivity to FR than 35S-HFR1 expression, and only seedlings expressing 35S-HFR1(DeltaN) display constitutive photomorphogenesis [2].
• Gene expression of CONSTITUTIVE PHOTOMORPHOGENESIS AND DWARFISM involved in BR biosynthesis and phyB ACTIVATION-TAGGED SUPPRESSOR1 that inactivates BR was repressed and induced, respectively, in cdg1-D plants, suggesting constitutive activation of BR signaling in the mutant [3].

High impact information on COP1

• This constitutive photomorphogenic (COP) phenotype was not observed for mutants of cct1 corresponding to previously described cry1 alleles [4].
• COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively [5].
• Little is known regarding how light signals perceived by photoreceptors are transduced to regulate COP1 [6].
• Taken together, our results show that HFR1 is ubiquitinated by COP1 E3 ligase and marked for post-translational degradation during photomorphogenesis [2].
• COP10 is a ubiquitin-conjugating enzyme variant (UEV), which is thought to act together with COP1, DET1, and the COP9 signalosome (CSN) in Arabidopsis to repress photomorphogenesis [7].

Biological context of COP1

• Here we show that both photoactivated cryptochromes repress COP1 activity through a direct protein-protein contact and that this direct regulation is primarily responsible for the cryptochrome-mediated blue light regulation of seedling photomorphogenic development and genome expression profile [6].
• We propose that COP1 mediates light control of gene expression through targeted degradation of multiple photomorphogenesis-promoting transcription factors in the nucleus [8].
• Although epistasis of a putative null cop1-5 mutation over a hy5 mutation implied that COP1 acts downstream of HY5, the same hy5 mutation can suppress the dark photomorphogenic phenotypes (including hypocotyl elongation and cotyledon cellular differentiation) of the weak cop1-6 mutation [9].
• This relationship suggests a role for the ATH1 protein in the signal transduction pathway downstream of COP1 [10].
• The subnuclear localization signal overlaps two previously characterized motifs, a cytoplasmic localization signal and a putative alpha-helical coiled-coil domain that has been implicated in COP1 dimerization [11].

Anatomical context of COP1

• Upon light exposure, COP1 migrates to the cytosol allowing photomorphogenesis to proceed but the residual nuclear pool down-regulates light signaling mediated by phytochrome A. Here we show that weak alleles of cop1 exhibit reverse photomorphogenic responses i.e. reduced rather than enhanced cotyledon unfolding under red light compared to darkness [12].
• For the two mutants studied (cpd: constitutive photomorphogenesis and dwarfism; bril: brassinosteroid insensitive), hypocotyl length was correlated to P(os) for the protoplasts [13].

Associations of COP1 with chemical compounds

• The phyA PAS domain interacts with the COP1 WD40 domain [14].
• Our data suggest that FIN219 may define a critical link for phytochrome A-mediated far-red inactivation of COP1 and a possible cross-talk juncture between auxin regulation and phytochrome signaling [15].
• COP1 possesses a leucine-rich nuclear-exclusion signal that resides in a domain implicated in COP1 dimerization [16].
• COP1, another COP/DET/FUS protein, is itself not a subunit of the COP9 signalosome [17].
• One of the isolated mutants, eid6, is a novel recessive allele of the COP1 gene (constitutive photomorphogenic 1) that carries an amino acid transition in a conserved histidine residue of the RING finger domain [18].

Physical interactions of COP1

• Coimmunoprecipitation studies showed that CRY1 was bound to COP1 in extracts from both dark- and light-grown Arabidopsis [19].
• It was shown that in the dark, COP1 directly interacts with the bZIP transcription factor HY5, a positive regulator of photomorphogenesis, and promotes its proteasome-mediated degradation [8].
• The SPA2 protein is constitutively nuclear localized in planta and can physically interact with the repressor COP1 [20].
• The Arabidopsis CIP7 protein was identified by its capability to interact with COP1 [21].
• COP10 is part of a nuclear protein complex and capable of directly interacting with both COP1 and the COP9 signalosome [22].

Enzymatic interactions of COP1

• Both HFR1 and HFR1(DeltaN) can be ubiquitinated by COP1, although with different efficiencies [2].

Co-localisations of COP1

• A green fluorescent protein-COL3 fusion protein colocalizes with COP1 to nuclear speckles when transiently expressed in plant cells [23].

Regulatory relationships of COP1

• In transgenic plants, HFR1 levels are significantly elevated upon induced expression of a dominant-negative COP1 mutant that interferes with endogenous COP1 E3 activity [2].
• Taken together, our data indicate that CIP7 acts as a positive regulator of light-regulated genes and is a potential direct downstream target of COP1 for mediating light control of gene expression [21].
• Here, we show that COP1 negatively regulates HY5, a bZIP protein and a positive regulator of photomorphogenic development [24].
• The results indicate that COP1 is required to repress the AtMYB21 gene in seedlings, and the pleiotropic phenotypes shown in the cop1 mutant are due to the combination of misregulation of genuine light-signalling components and other tissue-specific factors [25].
• CIP4 expression is light inducible and regulated by COP1 [26].

Other interactions of COP1

• The signaling mechanism of Arabidopsis CRY1 involves direct interaction with COP1 [19].
• SUPPRESSOR OF PHYTOCHROME A-105 family proteins (SPA1 to SPA4) that are required for COP1 function in dark and visible light are not essential in the response to UV-B [27].
• We demonstrate that accumulation of PIF3 in the nucleus in dark requires constitutive photomorphogenesis 1 (COP1), a negative regulator of photomorphogenesis, and show that red (R) and far-red light (FR) induce rapid degradation of the PIF3 protein [28].
• 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 [29].
• COP1 specifically targets HY5 for degradation via the 26S proteasome in the dark through their direct physical interaction [6].

Analytical, diagnostic and therapeutic context of COP1

• Functional dissection of Arabidopsis COP1 reveals specific roles of its three structural modules in light control of seedling development [30].
• Evidence is presented for efficient association of the two sub-fragments of the split COP1 protein in Arabidopsis and in a yeast two-hybrid assay [31].
• BRET was applied in conjunction with site-directed mutagenesis to explore the respective contributions of the nuclear-exclusion and dimerization motifs to the regulation of COP1 activity in vivo [16].
• Allelism tests established that three fusca loci are represented by mutants previously described as defective in light-regulated responses [32].
• Molecular cloning and sequencing of the cDNA of cop1 gene from Pisum sativum [33].

References