SPA1 (SUPPRESSOR OF PHYA-105 1; At2g46340) is a nuclear repressor of light signaling in Arabidopsis thaliana and the founding member of the four-member SPA family (SPA1-SPA4). The protein has an N-terminal kinase-like domain, a central coiled-coil domain that binds the coiled-coil of the RING E3 ubiquitin ligase COP1, and a C-terminal WD40-repeat domain that resembles the COP1 WD40 domain and contains DDB1-binding (DWD/WDXR) motifs. SPA proteins form stable tetrameric COP1-SPA complexes that associate with CUL4-DDB1 to make CUL4-DDB1-COP1-SPA E3 ligases. In darkness, SPA1 enhances COP1-mediated ubiquitination and proteasomal degradation of photomorphogenesis-promoting transcription factors (HY5, HFR1, LAF1) and of the flowering regulator CONSTANS, repressing seedling de-etiolation and, in adult plants, short-day flowering. Photoactivated phytochromes (phyA in far-red, phyB in red light) and cryptochromes (CRY1, CRY2 in blue light) bind SPA1 and disrupt or reorganize the COP1-SPA1 interaction, inactivating the ligase so that its substrates accumulate. The N-terminal domain has been reported to act as a Ser/Thr kinase that phosphorylates PIF1 in a phyB-enhanced complex, promoting light-induced PIF1 degradation, and that also phosphorylates HY5 at Ser36; SPA1 thus acts at both arms of phytochrome signaling, COP1 inhibition and PIF turnover.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:11461903 The phytochrome A-specific signaling intermediate SPA1 inter... | MODIFY | Summary: Protein binding to COP1 (P43254). SPA1 binds COP1 via its coiled-coil domain and enhances COP1 E3 ligase activity; this is the central functional interaction of SPA1, but "protein binding" is uninformative. The informative MF is ubiquitin-protein transferase activator activity (stimulation of COP1 E3 activity). Reason: Replace generic protein binding by the activity the COP1 interaction supports: SPA1 stimulates COP1 E3 ubiquitin ligase activity. Proposed replacements: ubiquitin-protein transferase activator activity Supporting Evidence: PMID:11461903 we show that SPA1 strongly and selectively binds to COP1 PMID:12827204 SPA1 stimulates the E3 activity of residual nuclear COP1 to ubiquitinate LAF1 |
| GO:0005515 protein binding | IPI PMID:12827204 LAF1 ubiquitination by COP1 controls photomorphogenesis and ... | MODIFY | Summary: Protein binding to COP1 (P43254). SPA1 binds COP1 via its coiled-coil domain and enhances COP1 E3 ligase activity; this is the central functional interaction of SPA1, but "protein binding" is uninformative. The informative MF is ubiquitin-protein transferase activator activity (stimulation of COP1 E3 activity). Seo et al. showed the SPA1 coiled-coil facilitates COP1-dependent LAF1 ubiquitination. Reason: The paper directly shows SPA1 stimulates COP1 E3 activity on LAF1; the activator term is more informative. Proposed replacements: ubiquitin-protein transferase activator activity Supporting Evidence: PMID:12827204 The coiled-coil domain of SPA1, a negative regulator of phyA signalling, has no effect on COP1 auto-ubiquitination but facilitates LAF1 ubiquitination at low COP1 concentrations |
| GO:0005515 protein binding | IPI PMID:14597662 The COP1-SPA1 interaction defines a critical step in phytoch... | MODIFY | Summary: Protein binding to COP1 (P43254). SPA1 binds COP1 via its coiled-coil domain and enhances COP1 E3 ligase activity; this is the central functional interaction of SPA1, but "protein binding" is uninformative. The informative MF is ubiquitin-protein transferase activator activity (stimulation of COP1 E3 activity). Saijo et al. showed light-dependent COP1-SPA1 interaction and SPA1 alteration of COP1 E3 activity on HY5. Reason: Use the activator activity term rather than protein binding. Proposed replacements: ubiquitin-protein transferase activator activity Supporting Evidence: PMID:14597662 We further demonstrate the E3 ubiquitin ligase activity of COP1 on HY5 in vitro and the alteration of that activity by SPA1 |
| GO:0005515 protein binding | IPI PMID:15960622 Repression of light signaling by Arabidopsis SPA1 involves p... | REMOVE | Summary: Interaction with HFR1 (AT1G02340), a COP1-SPA substrate, shown by yeast two-hybrid and in vitro co-IP. Reflects substrate recognition by the COP1-SPA E3 ligase; "protein binding" itself is uninformative. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid experimental IPI; substrate-binding is part of SPA1 function but the generic term carries little information. Supporting Evidence: PMID:15960622 We show that SPA1 physically interacts with HFR1 in a yeast two-hybrid assay and an in vitro co-immunoprecipitation assay |
| GO:0005515 protein binding | IPI PMID:15960622 Repression of light signaling by Arabidopsis SPA1 involves p... | REMOVE | Summary: Same HFR1 (Q9FE22) interaction as the AT1G02340 row, recorded with the UniProt identifier. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Duplicate of the HFR1 interaction; substrate binding, non-core generic term. Supporting Evidence: PMID:15960622 higher levels of HFR1 protein accumulate in the spa1 mutant background under various light conditions |
| GO:0005515 protein binding | IPI PMID:16854975 Arabidopsis SPA proteins regulate photoperiodic flowering an... | REMOVE | Summary: Interaction with CONSTANS (AT5G15840) in vitro and in vivo via the CO CCT domain; CO is a COP1-SPA substrate in photoperiodic flowering. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Experimentally supported substrate interaction; relevant to the flowering role, which is non-core relative to the de-etiolation function, and the term is generic. Supporting Evidence: PMID:16854975 SPA proteins interact physically with CO in vitro and in vivo |
| GO:0005515 protein binding | IPI PMID:16854975 Arabidopsis SPA proteins regulate photoperiodic flowering an... | REMOVE | Summary: Interaction recorded with O50055 (COL1). The abstract reports the SPA1 interaction with CONSTANS (CO), a close COL1 paralog; whether COL1 itself was assayed cannot be seen from the abstract. UniProt independently records SPA1-COL1 as a binary interaction (O50055: COL1; NbExp=10), so the COL1 partner is supported by IntAct data and is not evidently an identifier mis-mapping. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Experimental IPI; defer to curators regarding the partner identifier. Generic term, non-core. Supporting Evidence: PMID:16854975 Domain mapping shows that the SPA1-CO interaction requires the CCT-domain of CO |
| GO:0005515 protein binding | IPI PMID:18812498 Biochemical characterization of Arabidopsis complexes contai... | REMOVE | Summary: Interaction with O50055 (COL1) from the biochemical characterization of COP1-SPA complexes. The abstract does not mention COL1; full text not reviewed for this partner. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Experimental IPI from a paper the curator read in full; generic term, non-core. Supporting Evidence: PMID:18812498 The four endogenous SPA proteins can form stable complexes with COP1 in vivo regardless of light conditions |
| GO:0005515 protein binding | IPI PMID:18812498 Biochemical characterization of Arabidopsis complexes contai... | MODIFY | Summary: Protein binding to COP1 (P43254). SPA1 binds COP1 via its coiled-coil domain and enhances COP1 E3 ligase activity; this is the central functional interaction of SPA1, but "protein binding" is uninformative. The informative MF is ubiquitin-protein transferase activator activity (stimulation of COP1 E3 activity). Zhu et al. showed endogenous SPA-COP1 complexes in vivo. Reason: SPA-COP1 complex formation underlies SPA1 stimulation of COP1 E3 ligase activity. Proposed replacements: ubiquitin-protein transferase activator activity Supporting Evidence: PMID:18812498 The four endogenous SPA proteins can form stable complexes with COP1 in vivo regardless of light conditions |
| GO:0005515 protein binding | IPI PMID:18812498 Biochemical characterization of Arabidopsis complexes contai... | REMOVE | Summary: Heteromeric interaction with SPA4 (Q94BM7); SPA proteins self-associate and interact with each other within COP1-SPA complexes. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid complex-assembly interaction; captured more informatively by complex membership (CUL4-RING E3 ligase complex). Supporting Evidence: PMID:18812498 The SPA proteins can self-associate or interact with each other, forming a heterogeneous group of SPA-COP1 complexes |
| GO:0005515 protein binding | IPI PMID:18812498 Biochemical characterization of Arabidopsis complexes contai... | REMOVE | Summary: Heteromeric interaction with SPA3 (Q9LJR3) within COP1-SPA complexes. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid complex-assembly interaction; generic term. Supporting Evidence: PMID:18812498 The SPA proteins can self-associate or interact with each other, forming a heterogeneous group of SPA-COP1 complexes |
| GO:0005515 protein binding | IPI PMID:21511871 Arabidopsis cryptochrome 1 interacts with SPA1 to suppress C... | REMOVE | Summary: Blue-light-dependent interaction with CRY1 (Q43125); photoexcited CRY1 binding to SPA1 suppresses the SPA1-COP1 interaction. This is the mechanism of photoreceptor inactivation of COP1-SPA. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid and functionally important photoreceptor interaction, but "protein binding" does not describe an activity of SPA1; no better MF term applies. Supporting Evidence: PMID:21511871 cryptochrome 1 (CRY1) undergoes blue-light-dependent interaction with the COP1-interacting protein SPA1 |
| GO:0005515 protein binding | IPI PMID:21511872 Blue-light-dependent interaction of cryptochrome 1 with SPA1... | REMOVE | Summary: Independent report of blue-light-dependent CRY1-SPA1 interaction that attenuates COP1-SPA1 association. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid photoreceptor interaction; generic term. Supporting Evidence: PMID:21511872 CRY1 interacts physically with SPA1 in a blue-light-dependent manner |
| GO:0005515 protein binding | IPI PMID:21511872 Blue-light-dependent interaction of cryptochrome 1 with SPA1... | REMOVE | Summary: Interaction with CRY2 (Q96524) recorded from Lian et al.; the abstract focuses on CRY1, CRY2-SPA1 interaction is independently established (Zuo et al. 2011). Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Experimental IPI; defer to curator who read the full text; generic term. Supporting Evidence: PMID:21514160 Arabidopsis CRY2 (cryptochrome 2) undergoes blue light-dependent interaction with the COP1-interacting protein SUPPRESSOR OF PHYTOCHROME A 1 (SPA1) |
| GO:0005515 protein binding | IPI PMID:21514160 Blue light-dependent interaction of CRY2 with SPA1 regulates... | REMOVE | Summary: Blue-light-dependent CRY2-SPA1 interaction via the SPA1 N-terminal kinase-like domain, stimulating CRY2-COP1 interaction and suppressing CO proteolysis. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid photoreceptor interaction; generic term. Supporting Evidence: PMID:21514160 blue light-dependent CRY2-SPA1 interaction stimulates CRY2-COP1 interaction |
| GO:0005515 protein binding | IPI PMID:22739826 Degradation of Arabidopsis CRY2 is regulated by SPA proteins... | REMOVE | Summary: FRET-FLIM interaction of CRY2 with SPA1 in nuclei; SPA proteins required for blue-light CRY2 degradation. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid interaction (CRY2 is also a COP1-SPA substrate); generic term. Supporting Evidence: PMID:22739826 Fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy studies showed a robust physical interaction of cry2 with SPA1 in nuclei of living cells |
| GO:0005515 protein binding | IPI PMID:26120968 High-level expression and phosphorylation of phytochrome B m... | REMOVE | Summary: Interaction with phyB (AT2G18790): light-activated Pfr phyB inhibits COP1-SPA1 by direct interaction. Consistent with Sheerin et al. 2015 and Lu et al. 2015. Reason: Bare protein-binding row removed per project policy; removal does not mean the interaction is false. Valid photoreceptor interaction central to the phytochrome-COP1/SPA mechanism, but the generic binding term is not an activity of SPA1. Supporting Evidence: PMID:26120968 This response depends on the light-activated Pfr form of phyB that inhibits the function of the COP1-SPA1 complex by direct interactions PMID:25744387 the photoactivated phyB represses the association of SPA1 with COP1, which is mediated, at least in part, through red-light-dependent interaction of phyB with SPA1 |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: ATP binding inferred from the InterPro protein kinase domain (IPR000719) in the SPA1 N-terminus. Paik et al. 2019 reported autophosphorylation and Ser/Thr kinase activity of the SPA1 N-terminal domain, which implies ATP binding, but the kinase-like domain is atypical and ATP binding has not been measured directly. Reason: Plausible given reported kinase activity; kept as non-core pending direct biochemical confirmation. Supporting Evidence: PMID:31527679 SPA1 acts as a serine/threonine kinase and directly phosphorylates PIF1 in vitro and in vivo |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: Nuclear activity inferred phylogenetically for the SPA/COP1-like clade; consistent with direct localization data. Reason: Consistent with IDA nuclear localization and nuclear function of COP1-SPA. Supporting Evidence: PMID:10205059 SPA1 can localize to the nucleus |
| GO:0005634 nucleus | IDA PMID:10205059 SPA1, a WD-repeat protein specific to phytochrome A signal t... | ACCEPT | Summary: SPA1 localizes to the nucleus (original cloning paper). Reason: Direct localization evidence; nucleus is where COP1-SPA acts on transcription-factor substrates. Supporting Evidence: PMID:10205059 SPA1 can localize to the nucleus, suggesting a possible function in phytochrome A-specific regulation of gene expression |
| GO:0005634 nucleus | IDA PMID:22739826 Degradation of Arabidopsis CRY2 is regulated by SPA proteins... | ACCEPT | Summary: SPA1 interacts with CRY2 in nuclei of living cells (FRET-FLIM). Reason: Direct imaging evidence of nuclear SPA1. Supporting Evidence: PMID:22739826 robust physical interaction of cry2 with SPA1 in nuclei of living cells |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to nucleus. Reason: Consistent with experimental evidence. |
| GO:0005634 nucleus | ISM GO_REF:0000122 | ACCEPT | Summary: AtSubP predicted nuclear localization. Reason: Consistent with experimental evidence. |
| GO:0009637 response to blue light | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Response to blue light propagated across SPA family. SPA1 acts downstream of CRY1/CRY2 in blue light. Reason: Correct but SPA1 is a shared COP1-SPA component rather than a blue-light specific factor; blue light signaling is context for the phytochrome-focused core role. Supporting Evidence: PMID:21511872 SPA acts genetically downstream from CRYs to regulate light-controlled development |
| GO:0009637 response to blue light | IDA PMID:21511872 Blue-light-dependent interaction of cryptochrome 1 with SPA1... | KEEP AS NON CORE | Summary: Blue-light-dependent CRY1-SPA1 interaction attenuates COP1-SPA1 association. Reason: Valid; blue-light (cryptochrome) branch of SPA1 function. Supporting Evidence: PMID:21511872 Blue-light activation of CRY1 attenuates the association of COP1 with SPA1 in both yeast and plant cells |
| GO:0009637 response to blue light | IDA PMID:21514160 Blue light-dependent interaction of CRY2 with SPA1 regulates... | KEEP AS NON CORE | Summary: Blue-light-dependent CRY2-SPA1 interaction regulating COP1 and CO stability. Reason: Valid; cryptochrome branch. Supporting Evidence: PMID:21514160 SPA1 acts genetically downstream from CRY2 to mediate blue light suppression of the COP1-dependent proteolysis of the flowering-time regulator CONSTANS (CO) |
| GO:0009637 response to blue light | IMP PMID:21511871 Arabidopsis cryptochrome 1 interacts with SPA1 to suppress C... | KEEP AS NON CORE | Summary: Genetic evidence that SPA1 mediates CRY1-dependent blue-light suppression of COP1. Reason: Valid; cryptochrome branch. Supporting Evidence: PMID:21511871 the CRY1-SPA1 interaction suppresses the SPA1-COP1 interaction and COP1-dependent degradation of the transcription factor HY5 |
| GO:0009640 photomorphogenesis | IEA GO_REF:0000002 | MODIFY | Summary: Photomorphogenesis from InterPro family IPR044630 (SPA/COP1-related). SPA1 is a repressor of photomorphogenesis; the more precise term is negative regulation of photomorphogenesis. Reason: SPA1 represses photomorphogenesis rather than executing it. Proposed replacements: negative regulation of photomorphogenesis Supporting Evidence: PMID:10205059 functions in repression of photomorphogenesis |
| GO:0009640 photomorphogenesis | IMP PMID:10205059 SPA1, a WD-repeat protein specific to phytochrome A signal t... | MODIFY | Summary: spa1 mutants show enhanced photomorphogenesis in far-red light; SPA1 represses photomorphogenesis. acts_upstream_of_or_within photomorphogenesis is correct but the direction is better captured by negative regulation. Reason: Use the directional regulation term. Proposed replacements: negative regulation of photomorphogenesis Supporting Evidence: PMID:10205059 functions in repression of photomorphogenesis and is required for normal photosensory specificity of phytochrome A |
| GO:0009648 photoperiodism | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Photoperiodism propagated phylogenetically; SPA1 is required for photoperiodic flowering via CO stability. Reason: Supported for SPA1 by mutant evidence but secondary to the seedling light-signaling role. Supporting Evidence: PMID:16854975 Among the four SPA genes, SPA1 is necessary and sufficient for normal photoperiodic flowering |
| GO:0009658 chloroplast organization | IMP PMID:22383539 Plastids are major regulators of light signaling in Arabidop... | MARK AS OVER ANNOTATED | Summary: Chloroplast organization from a large-scale T-DNA screen for enhanced de-etiolation (end) mutants. Enhanced chloroplast biogenesis in spa1 is an indirect consequence of derepressed photomorphogenesis. Reason: SPA1 does not participate in chloroplast organization; the phenotype is downstream of its light-signaling repressor role. Supporting Evidence: PMID:22383539 We found that a high proportion of these mutant alleles induce chloroplast biogenesis during deetiolation |
| GO:0010017 red or far-red light signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Red or far-red light signaling pathway propagated phylogenetically. SPA1 acts in phyA (far-red) and phyB (red) signaling as the target of photoactivated phytochromes. Reason: Core: SPA1 is a direct target of photoactivated phyA/phyB within the R/FR signaling pathway. Supporting Evidence: PMID:25627066 light-activated phytochrome A (phyA) and phytochrome B (phyB) interact with SPA1 and other SPA proteins |
| GO:0010017 red or far-red light signaling pathway | IMP PMID:16891401 Functional profiling reveals that only a small number of phy... | ACCEPT | Summary: Functional profiling of phy-regulated early response genes; SPA1 cited among genes with deetiolation phenotypes. Reason: Consistent with extensive genetic evidence for SPA1 acting in phytochrome signaling. Supporting Evidence: PMID:16891401 HY5 and SPA1 , had been identified even earlier in forward genetics screens as having important roles in phy-regulated seedling deetiolation |
| GO:0010100 negative regulation of photomorphogenesis | IMP PMID:16813572 The central coiled-coil domain and carboxyl-terminal WD-repe... | ACCEPT | Summary: SPA1 overexpression causes hyperetiolation and reduced HY5/HFR1; SPA1 coiled-coil and WD domains repress photomorphogenesis in a COP1-dependent manner. Reason: Core biological role of SPA1. Supporting Evidence: PMID:16813572 overexpression of Arabidopsis SPA1 results in a hyperetiolation phenotype and reduced accumulation of HY5 and HFR1 |
| GO:0010114 response to red light | IEP PMID:17076805 phyA dominates in transduction of red-light signals to rapid... | KEEP AS NON CORE | Summary: SPA1 transcript is a rapid early-response gene to red light (expression-profiling evidence), part of negative feedback on light signaling. Reason: IEP for transcriptional responsiveness; correct but non-core. Supporting Evidence: PMID:17076805 we have examined the genome-wide expression profiles of genes responding to Rc within 1 h (early response genes) |
| GO:0010218 response to far red light | IEP PMID:17076805 phyA dominates in transduction of red-light signals to rapid... | KEEP AS NON CORE | Summary: Far-red response by expression profiling; the cited study used continuous red light, so the far-red assignment cannot be confirmed from the abstract, but SPA1 is a well-known phyA-regulated gene. Reason: Expression response; defer to curator who read the full text; non-core. Supporting Evidence: PMID:17076805 phyA has a quantitatively dominant role in Rc-induced expression of these early response genes |
| GO:0016604 nuclear body | IDA PMID:21511872 Blue-light-dependent interaction of cryptochrome 1 with SPA1... | ACCEPT | Summary: SPA1 localizes to nuclear bodies (with CRY1). Nuclear bodies are also where phytochromes, COP1 and SPAs colocalize. Reason: Direct imaging; consistent with Sheerin et al. 2015 phytochrome-SPA nuclear body colocalization. Supporting Evidence: PMID:25627066 SPAs and phytochromes colocalize and interact in nuclear bodies |
| GO:0016607 nuclear speck | IEA GO_REF:0000044 | MODIFY | Summary: Nuclear speck from UniProt subcellular location mapping. SPA1 forms nuclear bodies/speckles in plant cells; "nuclear speck" in GO denotes splicing-factor speckles, which is not demonstrated for SPA1. Reason: The demonstrated structures are photobody-type nuclear bodies; nuclear body is the appropriate term. Proposed replacements: nuclear body Supporting Evidence: PMID:25627066 SPAs and phytochromes colocalize and interact in nuclear bodies |
| GO:0042802 identical protein binding | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: Identical protein binding by ARBA; SPA1 self-association is experimentally reported. Reason: Correct but uninformative; complex assembly feature. Supporting Evidence: PMID:18812498 The SPA proteins can self-associate or interact with each other |
| GO:0042802 identical protein binding | IPI PMID:18812498 Biochemical characterization of Arabidopsis complexes contai... | KEEP AS NON CORE | Summary: SPA1 self-association within COP1-SPA complexes. Reason: Correct; structural feature of the complex, not core activity. Supporting Evidence: PMID:18812498 The SPA proteins can self-associate or interact with each other |
| GO:0048575 short-day photoperiodism, flowering | IMP PMID:16709190 The Arabidopsis SPA1 gene is required for circadian clock fu... | KEEP AS NON CORE | Summary: spa1-3 flowers early in short days with elevated FT; SPA1 also affects circadian period. Reason: Valid adult-plant role, secondary to the seedling photomorphogenesis function; acts via CO degradation. Supporting Evidence: PMID:16709190 the spa1-3 mutant flowers early under short-day (SD) but not long-day (LD) conditions |
| GO:0080008 Cul4-RING E3 ubiquitin ligase complex | ISS PMID:18223036 Characterization of Arabidopsis and rice DWD proteins and th... | ACCEPT | Summary: Cul4-RING E3 ubiquitin ligase complex by similarity to DWD substrate receptors (PRL1). Directly confirmed by Chen et al. 2010 (CUL4-DDB1 associates with COP1-SPA via WDXR motifs of SPA1) and Zhu et al. 2015 (CUL4-COP1-SPA E3 ligase degrades PIF1). Reason: Complex membership experimentally confirmed for SPA1. Supporting Evidence: PMID:20061554 The interactions between DDB1 and COP1, SPA1, and SPA3 were disrupted by mutations in the WDXR motifs of MBP-COP1, His-SPA1, and His-SPA3 PMID:26037329 the CUL4(COP1-SPA) E3 ubiquitin ligase is necessary for the light-induced degradation of PIF1 in Arabidopsis |
| GO:2000028 regulation of photoperiodism, flowering | IDA PMID:21514160 Blue light-dependent interaction of CRY2 with SPA1 regulates... | KEEP AS NON CORE | Summary: CRY2-SPA1 interaction controls COP1-mediated CO proteolysis and flowering. Reason: Valid; flowering role is secondary. Supporting Evidence: PMID:21514160 We demonstrate that SPA1 acts genetically downstream from CRY2 to mediate blue light suppression of the COP1-dependent proteolysis of the flowering-time regulator CONSTANS (CO) |
| GO:2000028 regulation of photoperiodism, flowering | IMP PMID:16854975 Arabidopsis SPA proteins regulate photoperiodic flowering an... | KEEP AS NON CORE | Summary: spa1 and spa1 spa3 spa4 mutants flower early in SD with increased CO protein. Reason: Valid; flowering role is secondary. Supporting Evidence: PMID:16854975 SPA proteins regulate photoperiodic flowering by controlling the stability of the floral inducer CO |
| GO:0004674 protein serine/threonine kinase activity | IDA PMID:31527679 A phyB-PIF1-SPA1 kinase regulatory complex promotes photomor... | NEW | Summary: Purified SPA1 N-terminal domain autophosphorylates and phosphorylates MBP and PIF1 in vitro; the R517E mutant is impaired, and SPAs are needed for light-induced PIF1 phosphorylation in vivo. Reason: Direct biochemical evidence for a catalytic activity of SPA1 not represented in GOA, extended to HY5 and eIF2alpha substrates in later papers. Caveat: all reports involve one research group, and the kinase-like domain is atypical. Supporting Evidence: PMID:31527679 SPA1 acts as a serine/threonine kinase and directly phosphorylates PIF1 in vitro and in vivo PMID:33686674 SPAs can directly phosphorylate HY5 in vitro, and the phosphorylated HY5 is absent in the spaQ background in vivo PMID:38658612 SPA1 directly phosphorylates the eIF2Ξ± C-terminus under light conditions file:ARATH/SPA1/SPA1-deep-research-falcon.md Purified SPA1 directly transfers phosphate from ATP to the transcription factor |
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Download this section (compressed HTML)Q: Is the SPA1 N-terminal domain a bona fide protein kinase in vivo, given that Holtkotte et al. (2016) found deletion of the conserved kinase-like region tolerated while missense mutations were deleterious, suggesting a structural role?
Q: How do photoactivated phyA and phyB binding to SPA1 reorganize the tetrameric COP1-SPA complex, and is SPA1 the primary phytochrome contact in vivo?
Experiment: Quantitative phosphoproteomics of PIF1 in spaQ seedlings complemented with wild-type versus catalytically dead (ATP-binding lysine) SPA1 under red light pulses, to test whether SPA1 catalytic activity per se is required for PIF1 phosphorylation in vivo.
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