RCA (Rubisco activase) is a nuclear-encoded, chloroplast stroma-localized AAA+ ATPase chaperone that uses ATP hydrolysis to remodel the active sites of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), removing tightly bound inhibitory sugar-phosphates (ribulose-1,5-bisphosphate and, in some species, 2-carboxyarabinitol-1-phosphate) and thereby restoring and maintaining Rubisco carbamylation and carboxylation activity. By controlling the activation state of Rubisco it is a major determinant of the kinetics of photosynthetic induction and of the thermal sensitivity of photosynthesis. In Arabidopsis the protein is expressed as two isoforms generated by alternative splicing that differ only at the C-terminus: a larger alpha (Long) isoform and a smaller beta (Short) isoform. The alpha isoform carries a C-terminal extension with two redox-active cysteines whose disulfide is reduced by thioredoxin-f; this redox switch, together with the stromal ADP/ATP ratio, couples Rubisco activase ATPase and Rubisco-activation activity to the light-driven redox and energy status of the chloroplast stroma. RCA belongs to the AAA+ superfamily, with a P-loop nucleotide-binding domain, and is one of the most abundant soluble proteins in photosynthetic leaf tissue.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: RCA is an AAA+ ATPase with a P-loop (Walker A) nucleotide-binding motif; ATP binding is a core molecular function and is independently supported by an experimental (IDA) annotation and by the crystal structure. Reason: ATP binding is a well-established, structurally and experimentally documented core function of Rubisco activase as an AAA+ ATPase. Supporting Evidence: file:ARATH/RCA/RCA-notes.md ATP-binding Walker A / P-loop: BINDING 165..172 ligand ATP |
| GO:0009570 chloroplast stroma | IEA GO_REF:0000044 | ACCEPT | Summary: Chloroplast stroma is the authentic primary subcellular location of RCA, consistent with the UniProt-curated subcellular location and with multiple experimental (HDA) stromal proteomics annotations. Reason: Stroma is the bona fide site of action where RCA reactivates Rubisco; this electronic annotation agrees with curated and experimental evidence. Supporting Evidence: file:ARATH/RCA/RCA-notes.md UniProt SUBCELLULAR LOCATION: "Plastid, chloroplast stroma. file:ARATH/RCA/RCA-deep-research-falcon.md consistent with RCA's functional target (Rubisco) residing in the stromal compartment |
| GO:0010287 plastoglobule | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Plastoglobule localization derives from a UniProt subcellular-location mapping backed by a single plastoglobule proteomics study (PubMed:16461379). RCA is an extremely abundant stromal protein and is a common contaminant of subplastidial fractions; plastoglobule is a minor/incidental location rather than a site of Rubisco activation. Reason: Experimentally derived (UniProt ECO:0000269|PubMed:16461379) but not a core functional location; the relevant site of action is the stroma. The Falcon deep-research report independently flags this as higher-risk, noting it could not directly document RCA as a plastoglobule component in the proteomics evidence it examined; retained as non-core (not removed) given the curated UniProt assignment. Supporting Evidence: file:ARATH/RCA/RCA-notes.md plastoglobule (GO:0010287, UniProt-validated ECO:0000269|PubMed:16461379) file:ARATH/RCA/RCA-deep-research-falcon.md Plastoglobule annotation for RCA is higher risk unless supported by direct Arabidopsis localization/proteomics beyond the present evidence. |
| GO:0016887 ATP hydrolysis activity | IEA GO_REF:0000002 | ACCEPT | Summary: ATP hydrolysis is the catalytic activity that powers RCA's remodeling of Rubisco active sites; this is a core molecular function of the AAA+ ATPase and is experimentally documented in the activase literature. Reason: ATP hydrolysis is the energy-yielding step driving Rubisco reactivation and is intrinsic to RCA function. Supporting Evidence: PMID:10430961 the 46-kDa isoform has minimal ATP hydrolysis and Rubisco activation activity in comparison with the 43-kDa isoform file:ARATH/RCA/RCA-deep-research-falcon.md ATP hydrolysis is used to generate force for substrate remodeling |
| GO:0009505 plant-type cell wall | HDA PMID:16287169 Arabidopsis cell wall proteome defined using multidimensiona... | MARK AS OVER ANNOTATED | Summary: Detection of RCA in a cell-wall proteome is almost certainly abundant-protein contamination. RCA is a soluble stromal chloroplast protein and one of the most abundant proteins in leaves; it has no known role at the cell wall. Reason: High-throughput proteomic detection in a non-chloroplast fraction; biologically implausible as a genuine location for a stromal AAA+ ATPase. Retained (not removed) because it is an experimentally coded HDA annotation. Supporting Evidence: file:ARATH/RCA/RCA-notes.md RCA is one of the most abundant soluble leaf proteins and is a near-ubiquitous contaminant of subcellular proteomics fractions |
| GO:0009535 chloroplast thylakoid membrane | HDA PMID:15322131 New functions of the thylakoid membrane proteome of Arabidop... | KEEP AS NON CORE | Summary: RCA is a soluble stromal protein; its recovery in a thylakoid membrane proteome reflects loose/peripheral association or co-fractionation of an abundant stromal protein rather than an intrinsic membrane location. Reason: Plausible peripheral/co-fractionation signal within the chloroplast, but not the functional site (the stroma); retained as a non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md thylakoid / thylakoid membrane (GO:0009579, GO:0009535) file:ARATH/RCA/RCA-deep-research-falcon.md RCA can reversibly associate with thylakoid membranes under moderate heat stress and/or depending on stromal pH and ATP, but this appears conditional rather than its primary steady-state location. |
| GO:0048046 apoplast | HDA PMID:18538804 Hydroponic isotope labelling of entire plants (HILEP) for qu... | MARK AS OVER ANNOTATED | Summary: Apoplast detection of this abundant stromal chloroplast protein is best explained as contamination in a whole-plant proteomics workflow; RCA has no established extracellular function. Reason: High-throughput proteomic detection outside the chloroplast; biologically implausible localization for a stromal Rubisco activase. Retained as an HDA annotation rather than removed. Supporting Evidence: file:ARATH/RCA/RCA-notes.md place RCA outside the chloroplast: plant-type cell wall (GO:0009505, PMID:16287169), apoplast (GO:0048046, PMID:18538804) |
| GO:0009570 chloroplast stroma | HDA PMID:16207701 The oligomeric stromal proteome of Arabidopsis thaliana chlo... | ACCEPT | Summary: Experimental (HDA) detection in the oligomeric stromal proteome confirms the chloroplast stroma as the authentic, functionally relevant location of RCA, where it acts on stromal Rubisco. Reason: Stroma is the bona fide site of RCA function; supported by experimental stromal proteomics and consistent with curated UniProt location. Supporting Evidence: file:ARATH/RCA/RCA-notes.md Chloroplast stroma is the authentic primary location |
| GO:0005634 nucleus | HDA PMID:14617066 Analysis of the Arabidopsis nuclear proteome and its respons... | MARK AS OVER ANNOTATED | Summary: Detection of RCA in a nuclear proteome is best explained as contamination of nuclear preparations by the highly abundant stromal protein; RCA has no established nuclear function. Reason: High-throughput proteomic detection in a nuclear fraction; implausible genuine location for a transit-peptide-bearing chloroplast stromal protein. Retained as an HDA annotation rather than removed. Supporting Evidence: file:ARATH/RCA/RCA-notes.md nucleus (GO:0005634, PMID:14617066) |
| GO:0009535 chloroplast thylakoid membrane | HDA PMID:14729914 In-depth analysis of the thylakoid membrane proteome of Arab... | KEEP AS NON CORE | Summary: A second thylakoid membrane proteome detection of soluble stromal RCA; reflects peripheral association or co-fractionation rather than an intrinsic membrane location. Reason: Within-chloroplast co-fractionation signal; not the functional stromal site. Retained as a non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md thylakoid / thylakoid membrane (GO:0009579, GO:0009535) |
| GO:0009579 thylakoid | HDA PMID:16648217 High light response of the thylakoid proteome in arabidopsis... | KEEP AS NON CORE | Summary: Thylakoid proteome detection of soluble stromal RCA; a within-chloroplast co-fractionation signal rather than the functional location. Reason: Co-fractionation of an abundant stromal protein with the thylakoid; not the core functional site (stroma). Retained as non-core. Supporting Evidence: file:ARATH/RCA/RCA-notes.md thylakoid / thylakoid membrane (GO:0009579, GO:0009535) |
| GO:0009941 chloroplast envelope | HDA PMID:12766230 Proteomics of the chloroplast envelope membranes from Arabid... | KEEP AS NON CORE | Summary: Chloroplast envelope proteome detection of soluble stromal RCA; reflects stromal contamination of envelope membrane preparations rather than a genuine envelope location. Reason: Within-chloroplast co-fractionation of an abundant stromal protein; not the functional site. Retained as non-core. Supporting Evidence: file:ARATH/RCA/RCA-notes.md chloroplast envelope (GO:0009941) |
| GO:0009507 chloroplast | HDA PMID:18431481 Sorting signals, N-terminal modifications and abundance of t... | KEEP AS NON CORE | Summary: Correct but unspecific chloroplast localization; the more precise and functionally relevant term is chloroplast stroma, which is independently annotated. Reason: Accurate organelle assignment but less informative than chloroplast stroma; kept as a (general) non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md chloroplast (GO:0009507) |
| GO:0009570 chloroplast stroma | HDA PMID:18633119 Quantitative proteomics of a chloroplast SRP54 sorting mutan... | ACCEPT | Summary: Additional experimental (HDA) confirmation of chloroplast stroma as the authentic, functionally relevant location of RCA. Reason: Stroma is the bona fide site of RCA function; corroborated by multiple stromal proteomics datasets and curated UniProt location. Supporting Evidence: file:ARATH/RCA/RCA-notes.md Chloroplast stroma is the authentic primary location |
| GO:0009570 chloroplast stroma | HDA PMID:20061580 AT_CHLORO, a comprehensive chloroplast proteome database wit... | ACCEPT | Summary: Further experimental (HDA) support for chloroplast stroma localization from the AT_CHLORO subplastidial proteome database. Reason: Stroma is the functional site of RCA; well corroborated experimentally. Supporting Evidence: file:ARATH/RCA/RCA-notes.md Chloroplast stroma is the authentic primary location |
| GO:0009579 thylakoid | HDA PMID:18633119 Quantitative proteomics of a chloroplast SRP54 sorting mutan... | KEEP AS NON CORE | Summary: Thylakoid co-fractionation of soluble stromal RCA in a quantitative chloroplast proteomics study; not an intrinsic functional location. Reason: Within-chloroplast co-fractionation signal, not the core stromal site. Retained as non-core. Supporting Evidence: file:ARATH/RCA/RCA-notes.md thylakoid / thylakoid membrane (GO:0009579, GO:0009535) |
| GO:0009941 chloroplast envelope | HDA PMID:12938931 Proteomic study of the Arabidopsis thaliana chloroplastic en... | KEEP AS NON CORE | Summary: Second chloroplast envelope proteome detection of soluble stromal RCA; reflects stromal contamination of envelope preparations rather than a genuine envelope location. Reason: Within-chloroplast co-fractionation of an abundant stromal protein; not the functional site. Retained as non-core. Supporting Evidence: file:ARATH/RCA/RCA-notes.md chloroplast envelope (GO:0009941) |
| GO:0003729 mRNA binding | IDA PMID:32344669 Discovering the RNA-Binding Proteome of Plant Leaves with an... | KEEP AS NON CORE | Summary: RCA was captured in a proteome-wide RNA interactome capture (ptRIC) screen that recovered many photosynthetic/metabolic enzymes lacking canonical RNA-binding domains. This is an unconventional/moonlighting RNA-association observation of unclear physiological significance, not the core function. Reason: Supported by a high-throughput in vivo crosslinking assay but represents a moonlighting/unconventional activity; not RCA's established function. Supporting Evidence: PMID:32344669 a large number of proteins related to photosynthesis associate with RNA in vivo |
| GO:0005794 Golgi apparatus | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | MARK AS OVER ANNOTATED | Summary: Golgi detection in a membrane-protein oligomerization profiling study is best explained as contamination by the highly abundant stromal protein; RCA has no established Golgi function. Reason: High-throughput proteomic detection in a non-chloroplast compartment; biologically implausible for a stromal Rubisco activase. Retained as an HDA annotation rather than removed. Supporting Evidence: file:ARATH/RCA/RCA-notes.md Golgi apparatus (GO:0005794, PMID:28887381) |
| GO:0009507 chloroplast | HDA PMID:25293756 A proteomic strategy for global analysis of plant protein co... | KEEP AS NON CORE | Summary: Correct but unspecific chloroplast localization from a protein-complex proteomics study; the precise functional term is chloroplast stroma. Reason: Accurate organelle assignment but less informative than chloroplast stroma. Kept as a general non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md chloroplast (GO:0009507) |
| GO:0009507 chloroplast | ISM GO_REF:0000122 | KEEP AS NON CORE | Summary: Sequence-based (AtSubP) prediction of chloroplast localization, consistent with the N-terminal transit peptide. Correct but less specific than the experimentally supported chloroplast stroma term. Reason: Computational prediction agreeing with the true organelle but unspecific; kept as a general non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md transit peptide 1-58 |
| GO:0009507 chloroplast | IDA PMID:21219905 Protein N-acylation overrides differing targeting signals. | KEEP AS NON CORE | Summary: Direct (IDA) evidence places RCA in the chloroplast, confirming the organelle. The more specific functional term chloroplast stroma is separately annotated. Reason: Correct organelle assignment but less informative than chloroplast stroma; kept as a general non-core localization. Supporting Evidence: file:ARATH/RCA/RCA-notes.md chloroplast (GO:0009507) |
| GO:0009753 response to jasmonic acid | IEP PMID:21173027 The role of Arabidopsis Rubisco activase in jasmonate-induce... | KEEP AS NON CORE | Summary: RCA transcript and protein are down-regulated by jasmonate in a COI1-dependent manner. This documents that RCA expression responds to JA; it is a regulatory/physiological context rather than RCA's core molecular function. Reason: Expression-based (IEP) response of RCA to jasmonate; a peripheral regulatory context, not the gene's core function. Supporting Evidence: PMID:21173027 RCA was down-regulated at the levels of transcript and protein abundance by JA in a COI1-dependent manner |
| GO:0010150 leaf senescence | IMP PMID:21173027 The role of Arabidopsis Rubisco activase in jasmonate-induce... | KEEP AS NON CORE | Summary: Loss of RCA produces senescence-associated features and COI1-dependent JA repression of RCA contributes to JA-induced leaf senescence. This is a downstream physiological consequence of reduced photosynthetic capacity rather than a direct, core function of RCA. Reason: Genetically supported (IMP) involvement, but an indirect/downstream developmental role secondary to RCA's effect on photosynthesis. Supporting Evidence: PMID:21173027 loss of RCA led to typical senescence-associated features and that the COI1-dependent JA repression of RCA played an important role in JA-induced leaf senescence |
| GO:0009409 response to cold | IEP PMID:16923014 The chloroplast lumen and stromal proteomes of Arabidopsis t... | KEEP AS NON CORE | Summary: RCA abundance changes during cold acclimation in a chloroplast stromal proteomics study. This is an expression-pattern (IEP) observation of RCA among cold-responsive photosynthetic proteins, a peripheral regulatory context rather than a core function. Reason: Expression-based response to low temperature; a physiological context, not RCA's core molecular function. Supporting Evidence: PMID:16923014 identify proteins that changed in abundance in Arabidopsis chloroplasts during cold shock |
| GO:0010319 stromule | IDA PMID:16923014 The chloroplast lumen and stromal proteomes of Arabidopsis t... | UNDECIDED | Summary: A stromule (filamentous stroma-filled plastid extension) location is biologically plausible for a soluble stromal protein, since stromules are continuous with the stroma. However the cited reference (PMID:16923014) is a chloroplast stroma/lumen cold-acclimation proteomics study whose abstract does not mention stromules, so the supporting evidence for this specific term cannot be verified from the available text. Reason: Cannot verify the supporting evidence for this experimentally coded (IDA) annotation from the cached abstract; per guidelines, do not remove an unverifiable experimental annotation. Supporting Evidence: file:ARATH/RCA/RCA-notes.md the abstract describes a stromal/lumen proteomics study and does not mention stromules |
| GO:0005524 ATP binding | IDA PMID:16822862 Increased sensitivity of oxidized large isoform of ribulose-... | ACCEPT | Summary: Direct biochemical study of nucleotide binding by the large and small RCA isoforms, measuring ATP/ATPgammaS affinities. ATP binding is a core function of this AAA+ ATPase. Reason: Experimentally demonstrated core nucleotide-binding activity central to RCA's mechanism. Supporting Evidence: PMID:16822862 a lower ATP or adenosine 5'-O-(thiotriphosphate) (ATPgammaS) affinity of the oxidized large isoform than either the reduced form or the smaller isoform |
| GO:0043531 ADP binding | IDA PMID:16822862 Increased sensitivity of oxidized large isoform of ribulose-... | KEEP AS NON CORE | Summary: ADP binding was directly measured for both RCA isoforms; ADP is the product of ATP hydrolysis and a physiological inhibitor whose binding underlies the redox/energy regulation of the large isoform. This is a real activity but a facet of the ATPase cycle rather than the headline function. Reason: Experimentally supported nucleotide binding, but represents the product/ inhibitor side of the ATPase cycle rather than the core catalytic/activator role. Supporting Evidence: PMID:16822862 the ADP affinities of the small isoform and the reduced or oxidized large isoform were similar |
| GO:0046863 ribulose-1,5-bisphosphate carboxylase/oxygenase activator activity | IDA PMID:16822862 Increased sensitivity of oxidized large isoform of ribulose-... | ACCEPT | Summary: This is the defining, core molecular function of RCA - binding to and increasing Rubisco activity by ATP-dependent removal of inhibitory sugar-phosphates. Directly measured here as Rubisco activation activity of the recombinant isoforms. Reason: The term precisely captures RCA's signature function and is experimentally demonstrated; this is the headline molecular function of the gene. Supporting Evidence: PMID:16822862 increases its ADP sensitivity for both ATP hydrolysis and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation file:ARATH/RCA/RCA-notes.md Binds to and increases the activity of rubisco by the removal of otherwise inhibitory sugar phosphates file:ARATH/RCA/RCA-deep-research-falcon.md ATP binding/hydrolysis drives conformational work that remodels the Rubisco holoenzyme and promotes dissociation of inhibitory sugar-phosphates from Rubisco catalytic sites |
| GO:0030234 enzyme regulator activity | IDA PMID:10430961 Mechanism of light regulation of Rubisco: a specific role fo... | MODIFY | Summary: Enzyme regulator activity is a generic parent term. The supporting study shows RCA regulates Rubisco activity (light/redox-dependent activation), which is captured far more precisely by the specific child term ribulose-1,5-bisphosphate carboxylase/oxygenase activator activity (GO:0046863). Reason: Term is correct but overly general; should be replaced with the specific Rubisco activator activity term that describes the actual molecular function. Proposed replacements: ribulose-1,5-bisphosphate carboxylase/oxygenase activator activity Supporting Evidence: PMID:10430961 Rubisco activase regulates the activity of Rubisco in response to light-induced changes in both the ADP/ATP ratio and the redox potential via thioredoxin-f |
| GO:0009416 response to light stimulus | IEP PMID:8819320 Identification of an Arabidopsis thaliana ribulose-1,5-bisph... | KEEP AS NON CORE | Summary: RCA transcription is light-responsive (in part via phytochrome) and circadian-clock-regulated. This is an expression-pattern observation showing RCA gene expression responds to light, a regulatory context rather than RCA's core molecular function. Reason: Expression-based (IEP) light responsiveness of the RCA gene; peripheral regulatory context, not a core function. Supporting Evidence: PMID:8819320 Transcription of the Arabidopsis thaliana gene encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is organ-specific, light-responsive, and regulated by the circadian clock |
| GO:0019253 reductive pentose-phosphate cycle | IC PMID:10430961 Mechanism of light regulation of Rubisco: a specific role fo... | NEW | Summary: RCA maintains the activation state of Rubisco, the carboxylating enzyme that catalyzes the CO2-fixing step of the reductive pentose-phosphate (Calvin- Benson) cycle. There is no curated GOA annotation to this process, but it is the pathway in which RCA's molecular function is exercised; proposed as a new annotation. Reason: Captures the core biological process context of RCA - sustaining Rubisco carboxylation activity within the Calvin-Benson cycle. Supporting Evidence: PMID:10430961 Rubisco activase is a nuclear-encoded chloroplast protein that is required for the light activation of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in vivo file:ARATH/RCA/RCA-deep-research-falcon.md These phenotypes support RCA as essential for normal photosynthetic carbon assimilation in planta. |
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)