DWARF14 (AtD14) is the strigolactone (SL) receptor of Arabidopsis, a 267-residue alpha/beta-hydrolase-fold protein with a Ser97-His247-Asp218 catalytic triad in a hydrophobic ligand pocket. Binding of SL (and of the synthetic analog GR24) triggers a conformational change of the lid domain that allows D14 to associate with the F-box protein MAX2 (SCF(MAX2)/ASK1) and with the SMXL6/SMXL7/SMXL8 transcriptional co-repressors, leading to their polyubiquitination and proteasomal degradation. D14 also slowly hydrolyses the butenolide D-ring of SLs; whether hydrolysis (and a covalently linked D-ring intermediate) is required to activate signalling or mainly deactivates the hormone after signalling remains debated. D14 is found in the nucleus and cytoplasm, acts locally in the shoot rather than as a mobile signal, and is itself degraded in an SL- and MAX2-dependent manner as negative feedback. Loss of D14 causes increased shoot branching, altered leaf shape and insensitivity to SL; its paralog KAI2 mediates karrikin responses through the same F-box protein.
Definition: Combining with a strigolactone and transmitting the signal, typically by an SL-induced conformational change that promotes association with an F-box protein (MAX2/D3) and SMXL/D53-family co-repressors, leading to their ubiquitin-dependent degradation.
Justification: D14 orthologs in Arabidopsis, rice, petunia and pea are bona fide SL receptors, but GO has no SL-specific receptor MF; analogous terms exist for auxin (GO:0038198). The term would be a child of GO:0038023 signaling receptor activity.
Supporting Evidence:
Definition: Catalysis of the hydrolysis of the butenolide D-ring (a cyclic carboxylic ester) of a strigolactone, releasing the ABC-ring moiety and a hydroxy-butenolide D-ring product, typically via a Ser-His-Asp catalytic triad.
Justification: D14 hydrolyses GR24 and natural SLs; GO has only substrate-specific lactonase children of GO:0052689 carboxylic ester hydrolase activity (e.g. limonin-D-ring-lactonase activity) and none for strigolactone. The term would be a child of GO:0052689.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:26546446 Strigolactone Signaling in Arabidopsis Regulates Shoot Devel... | MODIFY | Summary: D14 interacts with the SMXL6/7/8 co-repressors in an SL (GR24)-enhanced manner (Y2H and co-IP in protoplasts); this is the receptor-target contact at the heart of SL signalling. Reason: The interaction is well supported and biologically central, but "protein binding" is uninformative. The SL-enhanced recruitment of SMXL targets is the output of D14 receptor activation, so the informative MF is signaling receptor activity (no SL-specific receptor term exists yet; see proposed_new_terms). Proposed replacements: signaling receptor activity Supporting Evidence: PMID:26546446 In response to rac -GR24 treatment, SMXL6 and SMXL7 directly interacted with D14 in yeast cells in a concentration-dependent manner |
| GO:0005515 protein binding | IPI PMID:26546446 Strigolactone Signaling in Arabidopsis Regulates Shoot Devel... | MODIFY | Summary: D14 interacts with the SMXL6/7/8 co-repressors in an SL (GR24)-enhanced manner (Y2H and co-IP in protoplasts); this is the receptor-target contact at the heart of SL signalling. Reason: The interaction is well supported and biologically central, but "protein binding" is uninformative. The SL-enhanced recruitment of SMXL targets is the output of D14 receptor activation, so the informative MF is signaling receptor activity (no SL-specific receptor term exists yet; see proposed_new_terms). Proposed replacements: signaling receptor activity Supporting Evidence: PMID:26546446 In response to rac -GR24 treatment, SMXL6 and SMXL7 directly interacted with D14 in yeast cells in a concentration-dependent manner |
| GO:0005515 protein binding | IPI PMID:26546446 Strigolactone Signaling in Arabidopsis Regulates Shoot Devel... | MODIFY | Summary: D14 interacts with the SMXL6/7/8 co-repressors in an SL (GR24)-enhanced manner (Y2H and co-IP in protoplasts); this is the receptor-target contact at the heart of SL signalling. Reason: The interaction is well supported and biologically central, but "protein binding" is uninformative. The SL-enhanced recruitment of SMXL targets is the output of D14 receptor activation, so the informative MF is signaling receptor activity (no SL-specific receptor term exists yet; see proposed_new_terms). Proposed replacements: signaling receptor activity Supporting Evidence: PMID:26546446 In response to rac -GR24 treatment, SMXL6 and SMXL7 directly interacted with D14 in yeast cells in a concentration-dependent manner |
| GO:0005515 protein binding | IPI PMID:27479325 DWARF14 is a non-canonical hormone receptor for strigolacton... | MODIFY | Summary: SL-induced D14-MAX2 interaction; the AtD14-D3-ASK1 complex was crystallised in the presence of SL. Reason: Correct and central to SL perception, but protein binding is uninformative. The SL-dependent association with MAX2 is the signalling step of the receptor. Proposed replacements: signaling receptor activity Supporting Evidence: PMID:27479325 Here we report the crystal structure of the strigolactone-induced AtD14-D3-ASK1 complex |
| GO:0005515 protein binding | IPI PMID:32612234 Extensive signal integration by the phytohormone protein net... | REMOVE | Summary: High-throughput Y2H interaction with HIPP26 from a phytohormone interactome map. Reason: Single binary interaction from a systematic screen with no functional follow-up for D14; protein binding adds no functional information. Removal does not imply the interaction is false. |
| GO:0005634 nucleus | EXP PMID:24610723 Strigolactone promotes degradation of DWARF14, an Ξ±/Ξ² hydrol... | ACCEPT | Summary: D14-GFP is detected in nucleus and cytoplasm, overlapping MAX2 distribution. Reason: Experimental localisation; nuclear D14 is functionally relevant since SMXL7 acts in the nucleus and nucleus-localised D14 interacts with SMXL7 and MAX2. Supporting Evidence: PMID:24610723 Our data show that D14 distribution in vivo overlaps with that reported for MAX2 at both the tissue and subcellular levels PMID:27317673 nucleus-localized D14 can physically interact with both SMXL7 and the MAX2 F-box protein in a SL-dependent manner |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to nucleus. Reason: Consistent with experimental nuclear localisation. |
| GO:0005737 cytoplasm | EXP PMID:24610723 Strigolactone promotes degradation of DWARF14, an Ξ±/Ξ² hydrol... | ACCEPT | Summary: D14-GFP is detected in nucleus and cytoplasm, overlapping MAX2 distribution. Reason: Experimental localisation; nuclear D14 is functionally relevant since SMXL7 acts in the nucleus and nucleus-localised D14 interacts with SMXL7 and MAX2. Supporting Evidence: PMID:24610723 Our data show that D14 distribution in vivo overlaps with that reported for MAX2 at both the tissue and subcellular levels PMID:27317673 nucleus-localized D14 can physically interact with both SMXL7 and the MAX2 F-box protein in a SL-dependent manner |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to cytoplasm. Reason: Consistent with experimental cytoplasmic localisation. |
| GO:0005737 cytoplasm | ISM GO_REF:0000122 | ACCEPT | Summary: AtSubP prediction of cytoplasm. Reason: Consistent with experimental cytoplasmic localisation of D14. |
| GO:0010223 secondary shoot formation | IBA GO_REF:0000033 | MODIFY | Summary: d14 loss-of-function mutants are highly branched; D14 acts locally in the shoot to suppress axillary bud outgrowth. Reason: D14 does not form secondary shoots; it restricts their outgrowth via SL signalling. The regulatory term regulation of secondary shoot formation describes the role better. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN005141523 Β· D14 clade node SUPPORTS TRANSFER D14 orthologs (rice D14 Q10QA5, AtD14) control shoot branching, so the transfer itself is sound; only the process term is imprecise (formation vs regulation). Proposed replacements: regulation of secondary shoot formation Supporting Evidence: PMID:24610723 Like MAX2, D14 is required locally in the aerial part of the plant to suppress shoot branching. |
| GO:0010223 secondary shoot formation | IMP PMID:22422982 The path from Ξ²-carotene to carlactone, a strigolactone-like... | MODIFY | Summary: d14 loss-of-function mutants are highly branched; D14 acts locally in the shoot to suppress axillary bud outgrowth. Reason: D14 does not form secondary shoots; it restricts their outgrowth via SL signalling. The regulatory term regulation of secondary shoot formation describes the role better. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN005141523 Β· D14 clade node SUPPORTS TRANSFER D14 orthologs (rice D14 Q10QA5, AtD14) control shoot branching, so the transfer itself is sound; only the process term is imprecise (formation vs regulation). Proposed replacements: regulation of secondary shoot formation Supporting Evidence: PMID:24610723 Like MAX2, D14 is required locally in the aerial part of the plant to suppress shoot branching. |
| GO:1901601 strigolactone biosynthetic process | IBA GO_REF:0000033 | REMOVE | Summary: IBA transfer of strigolactone biosynthetic process to D14 from rice D14 (Q10QA5). Reason: D14 acts downstream of SL synthesis as the receptor; d14 mutants are SL-insensitive, not SL-deficient, and accumulate SL precursors. Hydrolysis of SL by D14 is a perception/ deactivation step, not formation of strigolactone. The phylogenetic inference propagates a biosynthesis role that is not supported for the D14 clade. Propagation Review Root cause: SOURCE BAD Failure modes: ROLE CONFLATION Sources checked: UniProtKB:Q10QA5 Β· rice D14 SOURCE BAD Rice D14 is the SL receptor; an SL-biosynthesis annotation on it conflates the receptor/hydrolase role (or feedback effects on SL levels) with biosynthesis. PANTHER:PTN005141523 Β· D14 clade node SOURCE WEAK OR INFERRED Supporting Evidence: PMID:22357928 AtD14, is also necessary for normal strigolactone responses in seedlings and adult plants PMID:30643123 We also demonstrate that D14 can deactivate SLs by hydrolytic degradation after signal transmission. |
| GO:1901601 strigolactone biosynthetic process | IMP PMID:22422982 The path from Ξ²-carotene to carlactone, a strigolactone-like... | REMOVE | Summary: UniProt IMP annotation of strigolactone biosynthetic process citing the carlactone paper (Alder et al. 2012). Reason: D14 performs no step of strigolactone biosynthesis. The pathway that forms SL from beta-carotene is catalysed by D27, CCD7 and CCD8 (to carlactone) and then MAX1 and downstream oxidases/methyltransferases, as the cited paper's own abstract states; D14 acts downstream as the receptor, d14 mutants are SL-insensitive rather than SL-deficient, and D14's hydrolase converts SL into a covalently bound intermediate and inactive products (perception/deactivation, not formation of strigolactone). The full text of PMID:22422982 is not in the cache and is not open access (no PMC copy; publisher page paywalled), so the exact assay the UniProt curator used could not be inspected. The same paper also supports the IMP secondary shoot formation row above, which indicates the D14 assay was a branching phenotype (consistent with SL insensitivity of d14), not a biosynthetic measurement. In any case no d14 phenotype could show that D14 does any of the work of SL formation - a branching or SL-level phenotype in d14 reflects loss of perception or feedback on SL levels - so the assertion is contradicted on the same biological grounds as the IBA row above, independent of evidence code. Supporting Evidence: PMID:22422982 Strigolactones derive from carotenoids via a pathway involving the carotenoid cleavage dioxygenases 7 and 8 (CCD7 and CCD8) and the iron-binding protein D27. PMID:22357928 AtD14, is also necessary for normal strigolactone responses in seedlings and adult plants PMID:30643123 We also demonstrate that D14 can deactivate SLs by hydrolytic degradation after signal transmission. |
| GO:1902348 cellular response to strigolactone | IEP PMID:24610723 Strigolactone promotes degradation of DWARF14, an Ξ±/Ξ² hydrol... | ACCEPT | Summary: SL induces MAX2-dependent, proteasome-mediated degradation of D14, an expression-level response of the receptor to its ligand. Reason: D14 is the SL receptor and directly participates in the cellular response to strigolactone; the SL-triggered turnover is part of that signalling cycle. The acts_upstream_of_or_within qualifier is the one GOA assigned to this IEP row and is retained as-is; it is weaker than the direct involvement asserted in core_functions, which rests on the receptor evidence (PMID:27479325, PMID:30643123) rather than on this expression-pattern row. Supporting Evidence: PMID:24610723 We also identified a mechanism of SL-induced, MAX2-dependent proteasome-mediated degradation of D14. |
| GO:0038023 signaling receptor activity | IDA PMID:27479325 DWARF14 is a non-canonical hormone receptor for strigolacton... | NEW | Summary: D14 binds SL, undergoes an SL-dependent conformational change, and then recruits MAX2 and SMXL targets, transmitting the hormone signal. Reason: No GO molecular function term specific for strigolactone receptor activity exists; the parent signaling receptor activity (used as the parent of auxin receptor activity) is the best current fit. A specific term is proposed below. Supporting Evidence: PMID:27479325 reveal that Arabidopsis thaliana (At)D14 undergoes an open-to-closed state transition to trigger strigolactone signalling PMID:30643123 we show that an AtD14D218A catalytic mutant that lacks enzymatic activity is still able to complement the atd14 mutant phenotype in an SL-dependent manner |
| GO:0052689 carboxylic ester hydrolase activity | IDA PMID:23381136 Crystal structures of two phytohormone signal-transducing Ξ±/... | NEW | Summary: Recombinant AtD14 hydrolyses the butenolide (lactone) ring of GR24 to the ABC-ring and D-ring products via its Ser-His-Asp triad, albeit at a very low turnover. Reason: Directly demonstrated enzymatic activity on the lactone (cyclic carboxylic ester) of SL; GOA lacks any hydrolase MF for D14. Retained as a distinct activity from the receptor role because hydrolysis deactivates SL and may contribute to activation. Supporting Evidence: PMID:23381136 only the D14 proteins were able to hydrolyze GR24, demonstrating hormone substrate specificity for this class of signaling hydrolases |
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Download this section (compressed HTML)Q: Is D14 catalysis required for signalling in planta (CLIM model, Yao et al. 2016) or is intact SL binding sufficient, with hydrolysis serving mainly to deactivate the hormone (Seto et al. 2019)?
Q: What did the Alder et al. 2012 carlactone paper (PMID:22422982) assay on Arabidopsis D14 that underlies the UniProt IMP annotation to strigolactone biosynthetic process (GO:1901601), and should that result instead be captured as a response/signalling term (e.g. response to strigolactone), given that d14 mutants are SL-insensitive rather than SL-deficient?
Experiment: Knock-in catalytic-triad mutants (S97A, H247A, D218A) at the endogenous AtD14 locus, combined with quantitative SMXL7 degradation reporters and BRC1 expression, to separate binding-driven from hydrolysis-driven receptor activation.
Type: genetic complementation with biochemical readout
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