| Functional role / process | Molecular mechanism & key partners | Substrates / targets | Localization / dynamics | Key quantitative data / statistics | Most relevant recent (2024) evidence |
|---|---|---|---|---|---|
| Core E3 ligase architecture and light-signaling repressor | Arabidopsis COP1 is a ~76 kDa RING-type E3 ligase with N-terminal RING (E2 interaction), central coiled-coil (COP1 homo-/heterodimerization with SPA proteins), and C-terminal WD40 β-propeller for substrate/photoreceptor binding; COP1 acts with SPA proteins in a CUL4-DDB1-RBX1 E3 module; many client proteins use a VP motif recognized by the COP1 WD40 pocket | Canonical light-signaling regulators include HY5, HYH, LAF1, HFR1, PIF1; table evidence also supports BBX1/CONSTANS and PP2Cs ABI1/AHG3 as COP1/SPA-associated targets/partners | COP1 contains bipartite NLS plus cytoplasmic localization signal; light regulates nuclear import/export; nuclear-localized GFP-COP1 forms punctate speckles / nuclear bodies where signaling partners colocalize | Complex size reported for COP1-SPA tetramer ~440 kDa; dark-grown seedlings contain COP1 in a ~700-kDa multimeric complex | 2024-focused evidence remains consistent with this established architecture; recent work extends COP1 functions beyond transcription factor turnover to chromatin and RNA-processing control (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000004) |
| Chromatin remodeling in photomorphogenesis | COP1 directly binds, polyubiquitinates, and degrades VIL1 in the dark via the 26S proteasome; interaction maps to COP1 N-terminus (aa 1-282) and VIL1 N-terminus/PHD region; by removing VIL1 in darkness, COP1 limits VIL1/PRC2-dependent chromatin loop formation and H3K27me3 deposition at growth genes; phyB contributes to light-induced loop formation, while COP1 antagonizes this in darkness | VIL1 (direct substrate); downstream affected loci include growth-promoting genes such as ATHB2, EDF3, BIM1 | Model: in light, COP1 is excluded/depleted from nucleus while VIL1 accumulates and associates with active phyB to promote chromatin loops and repression; in dark, COP1 accumulates in nucleus, ubiquitinates VIL1, and loops destabilize | 3,368 genes identified as VIL1-dependent H3K27me3-enriched loci; 665 genes co-regulated by VIL1 and COP1; H3K27me3 significantly higher in cop1-4 at VIL1 loci (P = 3.8e−7) and in the 665-gene cluster (P = 6.8e−10); VIL1 degradation blocked by 40 μM bortezomib; quantification from 3 biological replicates; gene-expression assays used n = 3 biological replicates with 4 technical replicates each; hypocotyl assays measured 30 seedlings per line across 3 biological replicates | PNAS 2024 established COP1→VIL1 as a direct ubiquitination axis linking light signaling to Polycomb-associated chromatin remodeling and dynamic chromatin loop control (pqac-00000002, pqac-00000005, pqac-00000009, pqac-00000013, pqac-00000014, pqac-00000017) |
| RNA processing / spliceosome-dependent photomorphogenesis | Light-induced alternative splicing changes are mediated in part through a COP1-spliceosome axis; COP1-dependent ubiquitination/degradation of the plant-specific spliceosomal component DCS1 contributes to intron retention (IR) and nuclear detainment of intron-retained transcripts (IRTs), thereby reducing translation of light-signaling genes under photomorphogenic conditions | DCS1 (spliceosomal component regulated by COP1); IRT-regulated signaling transcripts highlighted include PIF4, RVE1, ABA3 | IRTs are predominantly nuclear-retained rather than cytoplasmic; dark-grown cop1-6 phenocopies light-grown WT for many IR features; DCS1 interacts with COP1 (Y2H/BiFC/Co-IP evidence in figure excerpt) | 1,625 nuclear IR events were light responsive and 1,594 were COP1 responsive; only ~4% of IR events were in cytoplasmic fraction; ~60% of IRTs including PIF4/RVE1/ABA3 were upregulated in light-grown WT and dark-grown cop1-6; ~55% overlap for nuclear IR events vs ~30% for cytoplasmic IR events; pif4 rve1 aba3 triple mutant hypocotyl length reduced to ~76% of WT in dark; RNA-seq used 3 biological replicates; DE genes called at adjusted FDR ≤ 0.05 and fold change ≥ 2 | Nature Communications 2024 expanded COP1 function from proteolysis of transcription factors to control of spliceosome activity and nuclear RNA detainment during photomorphogenesis (pqac-00000010, pqac-00000011, pqac-00000012) |
| HY5 proteostasis and antagonistic deubiquitination | COP1 ubiquitinates HY5, opposing photomorphogenesis; UBP14 directly binds HY5 and removes ubiquitin, stabilizing HY5, with stronger affinity for nonphosphorylated HY5 (HY5S36A) than phosphomimic HY5S36D; UBP14 and HY5 form a positive-feedback loop because HY5 promotes UBP14 expression/accumulation | HY5 (direct COP1 substrate; direct UBP14 substrate for deubiquitination) | Nuclear HY5 stabilization promotes light responses, especially during dark-to-light transition | In vivo HY5 stability assays used 1 mM cycloheximide with DMSO or 1 mM cycloheximide + 50 μM MG132 after dark-to-light transfer; sampled at 0, 2, 4 h; HY5S36A/S36D protein and ubiquitination time course sampled at 0, 4, 8 h; quantification from 3 independent experiments with means ± SD; significance tested by two-way ANOVA with Tukey multiple comparisons (P < 0.05) | PNAS 2024 sharpened the COP1-HY5 module by showing that HY5 abundance is also actively set by UBP14-mediated deubiquitination, especially for the nonphosphorylated active form (pqac-00000008, pqac-00000015, pqac-00000016) |


*Table: This table summarizes experimentally supported functions, mechanisms, localization, and recent 2024 findings for Arabidopsis thaliana COP1 (UniProt P43254). It emphasizes direct evidence for COP1’s canonical E3 ligase architecture plus newer chromatin and RNA-processing roles.*