FBL22 (At4g05490) is a predicted Arabidopsis F-box/LRR protein with an N-terminal F-box domain and five leucine-rich repeats. Its domain architecture and phylogenetic annotation support binding to the SCF ubiquitin ligase complex and a putative role in substrate recognition. The specific substrates, SCF partners and cellular location have not been established in the sources examined. FBL22 transcript abundance was reported to increase through a nitric-oxide-dependent pathway in cadmium-treated roots, but this expression result does not establish a protein-level role in cadmium tolerance or an independently measured ubiquitin ligase activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:1905761 SCF ubiquitin ligase complex binding | IBA GO_REF:0000033 | ACCEPT | Summary: The IBA assigns SCF ubiquitin ligase complex binding to FBL22. The UniProt record independently identifies an F-box domain at residues 24-71 and five LRRs, consistent with a putative SCF substrate-recognition protein. Reason: Retain the phylogenetically curated binding function: the observed domain architecture is compatible with the IBA and there is no target-specific evidence of functional loss. This is an inference, not a direct FBL22-SKP1 interaction assay. The title of PMID:11077244 alone cannot establish the interaction and is no longer used as a mechanistic quotation. The precise substrates and complex partners remain unresolved. Supporting Evidence: file:ARATH/FBL22/FBL22-uniprot.txt FT DOMAIN 24..71 FT /note="F-box" |
| GO:0005634 nucleus | ISM GO_REF:0000122 | MARK AS OVER ANNOTATED | Summary: Nuclear localization comes from an AtSubP sequence-based prediction. FBL22 is a soluble F-box/LRR protein with no signal peptide, transmembrane segment or organellar targeting feature, and no localization experiment has been reported. Reason: The prediction is not contradicted, since F-box proteins and SCF complexes act in the nucleus as well as the cytosol, and a soluble protein lacking targeting signals could be in either. But AtSubP selects one compartment for a protein whose location is unknown, and SCF family membership does not establish a nuclear-specific site of action. Removal would overstate the case against an uncontradicted prediction, while acceptance would overstate an unverified single-compartment assignment. Marking it as an over-annotation records that the nuclear assertion goes beyond the evidence. Supporting Evidence: file:ARATH/FBL22/FBL22-uniprot.txt PE 4: Predicted; |
| GO:0006511 ubiquitin-dependent protein catabolic process | TAS PMID:11019805 Protein degradation in signaling. | KEEP AS NON CORE | Summary: This TAS row was assigned from Callis and Vierstra (2000), a review of the ubiquitin/proteasome pathway in plant signaling, as part of early family-wide annotation of Arabidopsis F-box proteins. FBL22 has a PROSITE-defined F-box (residues 24-71) followed by five LRRs, the architecture of SCF substrate-recognition subunits. Reason: The claim is that FBL22 takes part in ubiquitin-dependent protein degradation as an F-box substrate adaptor. This follows from the same F-box architecture and phylogenetic inference that support the accepted core SCF ubiquitin ligase complex binding (IBA) row. An F-box/LRR protein recruits substrates to the SCF ligase, so it does part of the work of the process rather than being a substrate. Nothing contradicts the claim, but nothing gene-specific supports it either, so it is retained as non-core rather than accepted as a core function (core_functions lists only the SCF-binding MF). The evidence is family-level, as no FBL22 substrate, SCF assembly or degradation assay exists, and the full review text was not accessible. The term is kept at this general level rather than refined to SCF-dependent proteasomal catabolism, so that it does not go beyond the predicted evidence. Supporting Evidence: PMID:11019805 Recent studies have linked proteolysis by the ubiquitin/proteasome pathway to a variety of signaling pathways in higher plants. file:ARATH/FBL22/FBL22-uniprot.txt PE 4: Predicted; |
| GO:0006511 ubiquitin-dependent protein catabolic process | TAS PMID:11077244 F-box proteins in Arabidopsis. | KEEP AS NON CORE | Summary: Xiao and Jang (2000) classified the Arabidopsis F-box protein family, and UniProt cites this paper for FBL22 gene-family assignment and nomenclature. The TAS row records the expected role of a family member in ubiquitin-dependent protein turnover. Reason: This row shares its claim with the PMID:11019805 TAS row and is consistent with the accepted SCF-binding IBA. UniProt confirms that the paper places FBL22 in the F-box family, which is the basis of the TAS. The local record has no abstract and the publisher full text was not accessible, but the family assignment it supports is verified through UniProt. The F-box/LRR architecture makes participation in ubiquitin-dependent protein catabolism as a substrate adaptor the expected function, and no contrary evidence exists. The claim remains a family-level prediction without a gene-specific assay, so it is kept as non-core, matching the PMID:11019805 row. Supporting Evidence: file:ARATH/FBL22/FBL22-uniprot.txt GENE FAMILY, AND NOMENCLATURE. file:ARATH/FBL22/FBL22-uniprot.txt PE 4: Predicted; |
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Download this section (compressed HTML)Q: Which ASK/SKP1 partners and substrates interact with FBL22, and does it assemble into an active SCF complex?
Q: Does the NO-dependent increase in FBL22 transcript under cadmium treatment contribute to a measurable stress phenotype?
Q: Where does FBL22 localize under basal and cadmium/NO-treatment conditions?
Q: Do other Arabidopsis F-box/LRR proteins compensate for loss of FBL22?
Experiment: Co-immunoprecipitation of FBL22 with Arabidopsis SKP1/ASK proteins and CUL1 to confirm SCF complex assembly
Hypothesis: FBL22 associates with an SCF core through its F-box domain.
Experiment: FBL22-GFP fusion under native promoter to determine subcellular localization
Hypothesis: FBL22 has a reproducible cellular distribution that may change with stress.
Experiment: IP-MS interactomics or comparative ubiquitinomics in fbl22 loss-of-function lines to identify substrates
Hypothesis: Loss of FBL22 alters the abundance or ubiquitination of specific protein substrates.
Experiment: CRISPR knockout or T-DNA insertion alleles tested under cadmium stress and NO perturbation conditions
Hypothesis: FBL22 contributes to a cadmium/NO-dependent phenotype rather than merely responding transcriptionally.
Experiment: Yeast two-hybrid or split-ubiquitin screen using FBL22 LRR domain as bait to identify interacting substrates
Hypothesis: The LRR region contributes to selective substrate recognition.
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