CBL10 (CALCINEURIN B-LIKE PROTEIN 10; also SCaBP8, SOS3-LIKE CALCIUM BINDING PROTEIN 8) is a four-EF-hand calcium sensor of the plant calcineurin B-like family. Unlike CBL4/SOS3 it is not N-myristoylated; instead an N-terminal hydrophobic extension anchors it to membranes, placing it at the plasma membrane and at the tonoplast and endosomes. Upon salt-induced Ca2+ signals, Ca2+-bound CBL10 binds the NAF/FISL motif of the CBL-interacting protein kinase CIPK24/SOS2 (and of CIPK8), relieves kinase autoinhibition, and recruits the kinase to membranes. At the plasma membrane the CBL10-CIPK24 complex activates the Na+/H+ antiporter SOS1 for Na+ extrusion, mainly in shoots, complementing the root-predominant CBL4/SOS3 branch; at the tonoplast the complex has been proposed to regulate vacuolar Na+ sequestration. CIPK24 phosphorylates CBL10 at a C-terminal serine (Ser-247 in isoform 1), which stabilizes the complex at the membrane and is required for full salt tolerance. One study also reports that CBL10 binds the K+ channel AKT1 and inhibits its inward K+ currents independently of CIPKs, with in-planta support from overexpression lines only. Loss of CBL10 causes salt hypersensitivity in vegetative tissues with altered Na+ accumulation, and impairs reproductive development under salt.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005509 calcium ion binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of calcium ion binding for the CBL clade (PTN002507456); CBL10 itself is among the experimentally grounded members (it appears in its own WITH/FROM, reflecting its IDA annotation). Reason: CBL10 is an EF-hand calcineurin B-like calcium sensor and calcium binding has been shown directly (PMID:17449811). The IBA node placement is consistent with the conserved EF-hand fold of the whole CBL family. Core activity: Ca2+ binding is the input that switches CBL10 into its CIPK-activating state. Supporting Evidence: PMID:17449811 SCABP8 is further shown to bind calcium file:ARATH/CBL10/CBL10-uniprot.txt Belongs to the calcineurin regulatory subunit family |
| GO:0005509 calcium ion binding | IDA PMID:17449811 SCABP8/CBL10, a putative calcium sensor, interacts with the ... | ACCEPT | Summary: Direct demonstration that SCaBP8/CBL10 binds Ca2+ (Quan et al. 2007). Reason: The abstract states that SCaBP8 binds calcium; together with the four EF-hand architecture this is the defining sensor activity of CBL10. Core function. Supporting Evidence: PMID:17449811 SCABP8 is further shown to bind calcium |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro EF-hand/CNBL1-10 mapping to calcium ion binding. Reason: Consistent with the experimental IDA and the IBA for the same term; EF-hand 4 carries a canonical Ca2+-binding loop (UniProt BINDING 207-218) and Ca2+ binding was shown experimentally. Supporting Evidence: PMID:17449811 SCABP8 is further shown to bind calcium file:ARATH/CBL10/CBL10-uniprot.txt Belongs to the calcineurin regulatory subunit family |
| GO:0005513 detection of calcium ion | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that CBL family members act in detection of calcium ion. Reason: CBL10 is a calcium sensor whose ability to activate its partner kinase SOS2/CIPK24 is calcium dependent (PMID:17449811); sensing a cytosolic Ca2+ signal and translating it into kinase activation is the CBL role this term describes, and the IBA node (seeded by CBL family members) is sound for CBL10. Supporting Evidence: PMID:17449811 enhance SOS2 activity in a calcium-dependent manner PMID:17449811 SCABP8 is further shown to bind calcium |
| GO:0005515 protein binding | IPI PMID:17449811 SCABP8/CBL10, a putative calcium sensor, interacts with the ... | MODIFY | Summary: IPI interaction with CIPK24/SOS2 (Q9LDI3), shown in vitro and in vivo (Quan et al. 2007), where CBL10 also enhanced SOS2 kinase activity in a calcium-dependent manner. Reason: Bare protein binding is uninformative. The same paper shows that the interaction activates the kinase (calcium-dependent enhancement of SOS2 activity), so the informative molecular function is protein serine/threonine kinase activator activity (GO:0043539; CIPK24 is a Ser/Thr kinase, and the CBL4 review uses the same term), the CBL-CIPK activation step also used for the CBL sensor annoton in the SOS module. Proposed replacements: protein serine/threonine kinase activator activity Supporting Evidence: PMID:17449811 interact with SOS2 both in vitro and in vivo PMID:17449811 enhance SOS2 activity in a calcium-dependent manner |
| GO:0005515 protein binding | IPI PMID:17825054 The calcium sensor CBL10 mediates salt tolerance by regulati... | MODIFY | Summary: IPI interaction with CIPK24/SOS2 (Q9LDI3) reported by Kim et al. 2007, who placed the CBL10-CIPK24 complex at vacuolar compartments. Reason: Bare protein binding is uninformative. This paper (abstract-only in the cache) establishes the physical CBL10-CIPK24 interaction but its abstract does not itself demonstrate kinase activation, so the most specific function it supports is binding to a protein kinase (GO:0019901 protein kinase binding). The activator activity is captured from PMID:17449811. Proposed replacements: protein kinase binding Supporting Evidence: PMID:17825054 the CBL10 protein physically interacts with the salt-tolerance factor CIPK24 (SOS2) |
| GO:0005515 protein binding | IPI PMID:23331977 Calcineurin B-like protein CBL10 directly interacts with AKT... | MODIFY | Summary: IPI interaction with the inward-rectifying K+ channel AKT1 (AT2G26650), shown by Y2H, BiFC and co-IP (Ren et al. 2013); CBL10 inhibits AKT1 currents. Reason: Bare protein binding is uninformative. The paper shows that direct binding of CBL10 to AKT1 reduces AKT1-mediated inward K+ currents in oocytes and root protoplasts, independently of CIPK kinase activity. AKT1 is an inward-rectifying K+ channel, so the specific term is inward rectifier potassium channel inhibitor activity (GO:0070320), an is_a descendant of potassium channel inhibitor activity (GO:0019870). The finding is single-lab and has not been independently replicated, and its in-planta evidence comes from CBL10 overexpression lines rather than cbl10 loss-of-function plants (OpenScientist audit, 2026-10-24). It is therefore kept as an activity supported by direct assay but not treated as a core function. Proposed replacements: inward rectifier potassium channel inhibitor activity Supporting Evidence: file:ARATH/CBL10/CBL10-hypotheses/cbl10-akt1-inhibition/openscientist.md The in-planta support that does exist is overexpression-based, not derived from *cbl10*-null plants, so it cannot distinguish a physiological inhibitory role from an overexpression artifact. PMID:23331977 CBL10 directly interacted with AKT1, as verified in yeast two-hybrid, BiFC and co-immunoprecipitation experiments PMID:23331977 CBL10 impairs AKT1-mediated inward K+ currents PMID:23331977 CBL10 may compete with CIPK23 for binding to AKT1 and negatively modulate AKT1 activity |
| GO:0005634 nucleus | ISM GO_REF:0000122 | REMOVE | Summary: AtSubP computational prediction of nuclear localization. Reason: There is no experimental evidence for nuclear CBL10. Its N-terminal hydrophobic extension targets it to membranes (plasma membrane, tonoplast and endosomes) and the N-terminal 40 residues are necessary and sufficient for vacuolar/endosomal targeting. Batistic et al. 2010, which localized all ten Arabidopsis CBLs, is reflected in UniProt as tonoplast targeting for CBL10. The sequence-based prediction is contradicted by the experimental localization data. Supporting Evidence: file:ARATH/CBL10/CBL10-uniprot.txt The N-terminal 40 amino acids are necessary and sufficient for vacuolar and endosomal targeting PMID:19448033 SCaBP8 protein associates with the plasma membrane due to an N-terminal hydrophobic domain file:ARATH/CBL10/CBL10-uniprot.txt Exclusively targeted to the tonoplast when interacting with CIPK24 (PubMed:19832944) |
| GO:0005737 cytoplasm | IDA PMID:17449811 SCABP8/CBL10, a putative calcium sensor, interacts with the ... | KEEP AS NON CORE | Summary: Cytoplasmic (soluble) localization observed by Quan et al. 2007. Reason: A soluble pool of CBL10 exists alongside the membrane-bound pool (Lin et al. 2009), but the functional, SOS2-phosphorylated form is membrane-associated. The annotation is supported by the curator-read full text, but cytoplasm is not where CBL10 performs its core activity. Supporting Evidence: PMID:19448033 SCaBP8 protein is present in both soluble and membrane fractions PMID:19448033 the phosphorylated form of SCaBP8 is found exclusively in the membrane fraction |
| GO:0005768 endosome | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular-location mapping to endosome, based on punctate (endosome/PVC) GFP signals (Kim et al. 2007; Batistic et al. 2010). Reason: Endosomal localization is experimentally reported and the N-terminal targeting region directs CBL10 to vacuolar and endosomal membranes, but the functionally characterized sites of action are the plasma membrane and the tonoplast. Supporting Evidence: file:ARATH/CBL10/CBL10-uniprot.txt PubMed:17825054 shows a vacuole membrane and endosome localization file:ARATH/CBL10/CBL10-uniprot.txt The N-terminal 40 amino acids are necessary and sufficient for vacuolar and endosomal targeting |
| GO:0005774 vacuolar membrane | IEA GO_REF:0000044 | MODIFY | Summary: UniProt subcellular-location mapping to vacuole membrane. Reason: Correct but general. In plants the experimentally supported term is plant-type vacuole membrane (GO:0009705), an is_a descendant of vacuolar membrane that CBL10 already carries by IDA (PMID:17825054) and IBA. Proposed replacements: plant-type vacuole membrane Supporting Evidence: PMID:17825054 the CBL10-CIPK24 (SOS2) complex is associated with the vacuolar compartments that are responsible for salt storage and detoxification in plant cells file:ARATH/CBL10/CBL10-uniprot.txt Exclusively targeted to the tonoplast when interacting with CIPK24 (PubMed:19832944) |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of plasma membrane activity for CBL family members. Reason: CBL10 associates with the plasma membrane via its N-terminal hydrophobic domain and recruits SOS2 there to activate the SOS1 Na+/H+ antiporter; CBL10 appears among the experimental donors for this IBA. Supporting Evidence: PMID:17449811 recruit SOS2 to the plasma membrane PMID:19448033 SCaBP8 protein associates with the plasma membrane due to an N-terminal hydrophobic domain |
| GO:0005886 plasma membrane | IDA PMID:17449811 SCABP8/CBL10, a putative calcium sensor, interacts with the ... | ACCEPT | Summary: Plasma membrane localization of SCaBP8/CBL10 and recruitment of SOS2 to the plasma membrane (Quan et al. 2007). Reason: Directly observed; CBL10 association with the plasma membrane is resistant to high salt and detergent and is required for activation of SOS1-mediated Na+/H+ exchange in shoots (Lin et al. 2009). Supporting Evidence: PMID:17449811 recruit SOS2 to the plasma membrane PMID:19448033 SCaBP8 protein associates with the plasma membrane due to an N-terminal hydrophobic domain PMID:19448033 Na + /H + exchange at the plasma membrane of Arabidopsis is severely reduced in the scabp8 mutant |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to cell membrane. Reason: Consistent with the IDA and IBA plasma membrane annotations. Supporting Evidence: PMID:17449811 recruit SOS2 to the plasma membrane |
| GO:0005886 plasma membrane | ISM GO_REF:0000122 | ACCEPT | Summary: AtSubP prediction of plasma membrane localization. Reason: The prediction agrees with experimental plasma membrane localization (PMID:17449811, PMID:19448033). Supporting Evidence: PMID:19448033 SCaBP8 protein associates with the plasma membrane due to an N-terminal hydrophobic domain |
| GO:0009705 plant-type vacuole membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of tonoplast activity for a CBL subclade (PTN008589031) that includes the tonoplast-targeted CBL2, CBL3, CBL6 and CBL10. Reason: CBL10 is targeted to the tonoplast by its N-terminal extension and is exclusively tonoplast-located when co-expressed with CIPK24; the IBA node agrees with the experimental data for CBL10 itself. Supporting Evidence: file:ARATH/CBL10/CBL10-uniprot.txt Exclusively targeted to the tonoplast when interacting with CIPK24 (PubMed:19832944) PMID:17825054 the CBL10-CIPK24 (SOS2) complex is associated with the vacuolar compartments that are responsible for salt storage and detoxification in plant cells |
| GO:0009705 plant-type vacuole membrane | IDA PMID:17825054 The calcium sensor CBL10 mediates salt tolerance by regulati... | ACCEPT | Summary: The CBL10-CIPK24 complex is associated with vacuolar membranes (Kim et al. 2007). Reason: Experimentally observed and corroborated by Batistic et al. 2010 (tonoplast targeting via the N-terminal 40 residues). This is one of the two membranes at which CBL10 recruits CIPK24. Supporting Evidence: PMID:17825054 the CBL10-CIPK24 (SOS2) complex is associated with the vacuolar compartments that are responsible for salt storage and detoxification in plant cells file:ARATH/CBL10/CBL10-uniprot.txt Exclusively targeted to the tonoplast when interacting with CIPK24 (PubMed:19832944) |
| GO:0019722 calcium-mediated signaling | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro CNBL1-10 family mapping to calcium-mediated signaling. Reason: CBL10 decodes salt-induced Ca2+ signals by calcium-dependent activation of CIPK24 (and CIPK8); calcium-mediated signaling is an appropriate process for this calcium-sensor family. Supporting Evidence: PMID:17449811 enhance SOS2 activity in a calcium-dependent manner PMID:17825054 the calcineurin B-like protein (CBL) family represents a unique group of calcium sensors and plays a key role in decoding calcium transients by specifically interacting with and regulating a family of protein kinases (CIPKs) |
| GO:0019900 kinase binding | IEA GO_REF:0000002 | MODIFY | Summary: InterPro CNBL1-10 mapping to kinase binding. Reason: CBL10 does bind CIPK kinases (CIPK24, CIPK8), but the binding is functionally an activation: CBL10 enhances SOS2/CIPK24 activity in a calcium-dependent manner. The more informative supported term is protein serine/threonine kinase activator activity (GO:0043539; CIPK24 is a Ser/Thr kinase, and the CBL4 review uses the same term). Proposed replacements: protein serine/threonine kinase activator activity Supporting Evidence: PMID:17449811 enhance SOS2 activity in a calcium-dependent manner PMID:31858132 we found that only three, CBL1, CBL5, and CBL10, interacted with CIPK8 |
| GO:0042538 hyperosmotic salinity response | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of a role in hyperosmotic salinity response, grounded on CBL10 itself. Reason: cbl10/scabp8 mutants are salt hypersensitive, especially in shoots, and CBL10 acts in the SOS pathway with CIPK24 to protect shoots from salt. Core process. Supporting Evidence: PMID:17449811 functions mainly in the shoot response to salt toxicity PMID:17825054 Cbl10 mutant plants exhibited significant growth defects and showed hypersensitive cell death in leaf tissues under high-salt conditions |
| GO:0042538 hyperosmotic salinity response | IMP PMID:17825054 The calcium sensor CBL10 mediates salt tolerance by regulati... | ACCEPT | Summary: cbl10 mutants show growth defects and leaf cell death under high salt (Kim et al. 2007). Reason: Salt hypersensitivity of the loss-of-function mutant is reproduced in independent studies (Quan et al. 2007; Kim et al. 2007; Lin et al. 2009), and CBL10 participates directly by activating CIPK24 to regulate Na+ transport. Core process. Supporting Evidence: PMID:17825054 Cbl10 mutant plants exhibited significant growth defects and showed hypersensitive cell death in leaf tissues under high-salt conditions PMID:17449811 functions mainly in the shoot response to salt toxicity |
| GO:0043266 regulation of potassium ion transport | IMP PMID:23331977 Calcineurin B-like protein CBL10 directly interacts with AKT... | MODIFY | Summary: CBL10 overexpression reduces K+ content and causes low-K+ sensitivity; CBL10 inhibits AKT1 inward K+ currents (Ren et al. 2013). Reason: The direction of regulation is known: CBL10 binds AKT1 and impairs its inward K+ currents, so the more precise term is negative regulation of potassium ion transport (GO:0043267). Evidence comes from a single study using overexpression lines and heterologous electrophysiology; this is a secondary function relative to the SOS/salt role. The finding is single-lab and has not been independently replicated, and its in-planta evidence comes from CBL10 overexpression lines rather than cbl10 loss-of-function plants (OpenScientist audit, 2026-10-24). It is therefore kept as an activity supported by direct assay but not treated as a core function. Proposed replacements: negative regulation of potassium ion transport Supporting Evidence: file:ARATH/CBL10/CBL10-hypotheses/cbl10-akt1-inhibition/openscientist.md The in-planta support that does exist is overexpression-based, not derived from *cbl10*-null plants, so it cannot distinguish a physiological inhibitory role from an overexpression artifact. PMID:23331977 CBL10 impairs AKT1-mediated inward K+ currents PMID:23331977 CBL10 may compete with CIPK23 for binding to AKT1 and negatively modulate AKT1 activity |
| GO:0050801 monoatomic ion homeostasis | IMP PMID:17825054 The calcium sensor CBL10 mediates salt tolerance by regulati... | MODIFY | Summary: cbl10 mutants have altered Na+ content under normal and saline conditions (Kim et al. 2007). Reason: The phenotype and mechanism concern Na+ specifically (altered Na+ accumulation; regulation of Na+ sequestration and SOS1-mediated Na+ extrusion), so sodium ion homeostasis (GO:0055078) is the more informative descendant. Proposed replacements: sodium ion homeostasis Supporting Evidence: PMID:17825054 the cbl10 mutant, unlike other salt-sensitive mutants identified thus far, was significantly lower than in the wild type under either normal or high-salt conditions PMID:17825054 CBL10 and CIPK24 (SOS2) constitute a novel salt-tolerance pathway that regulates the sequestration/compartmentalization of Na(+) in plant cells |
| GO:0043495 protein-membrane adaptor activity | IDA PMID:19832944 CBL-mediated targeting of CIPKs facilitates the decoding of ... | NEW | Summary: CBL10 is targeted to the tonoplast (by S-acylation) and holds CIPK24 there; the N-terminal targeting signal of the CBL, not the kinase, sets where the CBL/CIPK complex sits. Reason: Records what CBL10 does in the tonoplast CBL10-CIPK24 complex beyond binding the kinase (the GO:0019901 MODIFY on the PMID:17825054 row). CBL10 carries the membrane anchor and positions its kinase partner at the membrane, which is protein-membrane adaptor activity. The CBL targeting paper (abstract only in cache) shows that the CBL N-terminal signal determines CBL/CIPK complex localization, and the curated UniProt note from the same paper states that CBL10 is targeted exclusively to the tonoplast when interacting with CIPK24. Supporting Evidence: PMID:19832944 distinct targeting signals located in the N-terminal domain of CBL proteins determine the spatially discrete localization of CBL/CIPK complexes file:ARATH/CBL10/CBL10-uniprot.txt Exclusively targeted to the tonoplast when interacting with CIPK24 (PubMed:19832944) PMID:17825054 the CBL10-CIPK24 (SOS2) complex is associated with the vacuolar compartments that are responsible for salt storage and detoxification in plant cells PMID:31441225 This study shows that Arabidopsis CBL10, through protein S-acylation by protein S-acyl transferase10, targets to the vacuolar membrane to confer salt tolerance. |
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Download this section (compressed HTML)Q: Does the CBL10-CIPK24 complex regulate a tonoplast Na+ transporter (e.g. NHX-type antiporters or V-ATPase) directly, given that tonoplast Na+/H+ exchange was reported unaltered in scabp8 while cbl10 shows altered Na+ accumulation?
Q: Which of the dual localizations (plasma membrane versus tonoplast/endosomes) predominates in shoot cells in vivo, and does the N-terminal isoform difference (isoform 1 versus isoform 2) bias targeting?
Q: Is CBL10 inhibition of AKT1 physiologically relevant at native expression levels in roots, where CBL10 expression is low?
Q: Which partner kinase or effector mediates the SOS2/SOS3-independent role of CBL10 in reproductive development under salt?
Experiment: Compare Na+/H+ exchange and Na+ content in tonoplast versus plasma-membrane vesicles from cbl10 lines complemented with compartment-restricted CBL10 variants (N-terminal targeting swaps) to separate the two branches.
Experiment: Test AKT1 inhibition in planta with native-promoter CBL10 complementation and AKT1-binding-deficient CBL10 mutants under low-K+ conditions.
Experiment: Identify CBL10 interactors in flowers under salt (e.g. proximity labelling) to find the SOS-independent reproductive partner.
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