UGT74C1 (At2g31790) is a soluble family 1 UDP-glycosyltransferase of the UGT74 clade that acts as a thiohydroximate S-glucosyltransferase in glucosinolate core structure biosynthesis. It transfers glucose from UDP-glucose to the sulfur of thiohydroximates (produced by the C-S lyase SUR1), forming desulfoglucosinolates that are then sulfated by desulfoglucosinolate sulfotransferases. UGT74C1 is specialized for, and co-expressed with, the methionine-derived (aliphatic) branch, whereas its paralog UGT74B1 is the principal enzyme of the core pathway and particularly of the tryptophan-derived (indole) branch; UGT74C1 functions as an accessory enzyme that can complement the chemotypes and phenotypes of ugt74b1 mutants when expressed and shows thiohydroximate glucosyltransferase activity in planta. Like other family 1 UGTs, it lacks a membrane anchor or targeting peptide and is expected to act in the cytosol.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference that family 1 plant UGTs act in the cytoplasm. UGT74C1 has no signal peptide, transit peptide or transmembrane segment, and plant secondary-metabolite UGTs of this family are soluble cytosolic enzymes. Reason: Retain the PAINT localization judgment for this soluble plant UGT lineage. The supported UGT74 biochemical role is compatible with cytoplasmic pathway organization, but the evidence does not warrant a more precise target-specific compartment here. Supporting Evidence: |
| GO:0005777 peroxisome | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | MARK AS OVER ANNOTATED | Summary: The microsome experiment does not independently establish peroxisome localization. Reason: Full-text inspection of PMID:28887381 shows that washed microsomes were profiled by chromatography and sucrose gradients, while subcellular labels were taken from SUBAcon and prior GFP data. The authors explicitly report that no organelle occupied a single gradient cluster. Detection or membrane association is meaningful, but assigning UGT74C1 specifically to peroxisome exceeds the spatial resolution of this experiment. This is not a claim that the detected protein is absent or that all additional localization is impossible; the unsupported compartment assignment, rather than the proteomic observation, is marked as over-annotated. Supporting Evidence: PMID:28887381 The proteins with known localizations had scattered distributions across the entire gradient and no organelle fell in a single cluster. PMID:28887381 We used SUBAcon localization predictions to analyze oligomerization as a function of subcellular localization (Fig. 7C). |
| GO:0008194 UDP-glycosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: UGT74C1 has demonstrated thiohydroximate S-glucosyltransferase function. Reason: Refine the generic UDP-glycosyltransferase term consistently with the UDP-glucosyltransferase row to the supported thiohydroximate beta-D-glucosyltransferase activity. Complementation and in planta activity support this specialization. Proposed replacements: thiohydroximate beta-D-glucosyltransferase activity Supporting Evidence: PMID:24779768 the ability of UGT74C1 to complement phenotypes and chemotypes of the ugt74b1-2 knockout mutant and to express thiohydroximate UGT activity in planta |
| GO:0009507 chloroplast | ISM GO_REF:0000122 | MARK AS OVER ANNOTATED | Summary: The AtSubP chloroplast prediction is not independently established. Reason: This ISM AtSubP prediction (GO_REF:0000122) has no independent plastid-localization evidence in the reviewed sources. A soluble UGT fold and absent annotated transit peptide do not prove exclusion from plastids, but they also do not substantiate the predicted compartment. Mark the positive chloroplast claim as over-annotated rather than describing an inaccessible publication; retain the established thiohydroximate glucosyltransferase activity independently. |
| GO:0035251 UDP-glucosyltransferase activity | IEA GO_REF:0000117 | MODIFY | Summary: ARBA machine-learning assignment of UDP-glucosyltransferase activity. Correct, and the direct parent of the specific activity demonstrated for UGT74C1: glucosylation of thiohydroximates to desulfoglucosinolates (thiohydroximate beta-D-glucosyltransferase activity, GO:0047251, EC 2.4.1.195). Reason: The annotation is sound but too general; UGT74C1 expresses thiohydroximate UGT activity in planta and complements ugt74b1, so the specific term GO:0047251 should be used. The comparator paralog UGT74B1 carries GO:0047251 by IDA. Proposed replacements: thiohydroximate beta-D-glucosyltransferase activity Supporting Evidence: PMID:24779768 Finally, the ability of UGT74C1 to complement phenotypes and chemotypes of the ugt74b1-2 knockout mutant and to express thiohydroximate UGT activity in planta provides conclusive evidence for UGT74C1 being an accessory enzyme in glucosinolate biosynthesis PMID:23144921 whereby UGT74C1 glucosylates methionine-derived thiohydroximates; UGT74B1 metabolizes tryptophan-derived thiohydroximates |
| GO:0080043 quercetin 3-O-glucosyltransferase activity | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT placement of flavonol 3-O-glucosyltransferase activity at a deep family 1 UGT node (donors from the UGT76E group). UGT74C1 has no reported flavonol activity; its demonstrated and physiologically relevant activity is S-glucosylation of thiohydroximates, and the UGT74 clade analysis singled out glucosinolate synthesis as its role. Reason: Family 1 UGTs are often promiscuous toward flavonols in vitro, so a latent activity cannot be excluded, but there is no target-specific evidence and the inherited assertion does not describe UGT74C1's biological function. Not removed because divergence has not been demonstrated directly for this node. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN005361987 · PTN005361987 UNRESOLVED Deep family 1 UGT node seeded by UGT76E flavonol glucosyltransferases; whether the UGT74 thiohydroximate clade retains quercetin 3-O activity is untested. Supporting Evidence: PMID:24779768 Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates |
| GO:0080044 quercetin 7-O-glucosyltransferase activity | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT placement of quercetin 7-O-glucosyltransferase activity at the same deep family 1 UGT node. No flavonol glucosylation has been reported for UGT74C1; its role is thiohydroximate S-glucosylation in aliphatic glucosinolate synthesis. Reason: Promiscuous in vitro flavonol activity is common in family 1 UGTs, but there is no evidence for this activity in UGT74C1 and it does not describe the gene's function. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN005361987 · PTN005361987 UNRESOLVED Deep family 1 UGT node with flavonol-active donors including UGT74F1 (AT2G43840); UGT74C1-specific flavonol activity has not been tested. Supporting Evidence: PMID:24779768 Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates |
| GO:0019761 glucosinolate biosynthetic process | IMP PMID:24779768 Comparative analysis of Arabidopsis UGT74 glucosyltransferas... | NEW | Summary: UGT74C1 catalyzes the S-glucosylation step of glucosinolate core structure formation (thiohydroximate to desulfoglucosinolate). Genetic analysis of the UGT74 clade shows a special role in aliphatic glucosinolate synthesis, and UGT74C1 complements ugt74b1 glucosinolate chemotypes. Reason: Participation test: UGT74C1 itself catalyzes a step of the pathway (S-glucosylation of the thiohydroximate), so it is not merely a substrate or regulator. Comparator check: the other enzymes in the same role and pathway position carry this term - the paralog UGT74B1 (IMP and IBA), and CYP83A1, CYP79F1/F2 and SUR1 at adjacent steps - so its absence for UGT74C1 is a gap rather than a convention. Supporting Evidence: PMID:24779768 Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates, a conclusion strongly supported by phylogenetic and gene expression analyses. PMID:24779768 provides conclusive evidence for UGT74C1 being an accessory enzyme in glucosinolate biosynthesis |
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Download this section (compressed HTML)Q: What are the kinetic parameters and chain-length preferences of recombinant UGT74C1 toward short- versus long-chain methylthioalkyl thiohydroximates compared with UGT74B1?
Q: Under which environmental conditions does UGT74C1 contribute measurably to aliphatic glucosinolate flux in wild-type plants where UGT74B1 is present?
Experiment: Express recombinant UGT74C1 and UGT74B1 and determine kinetics on a panel of synthetic aliphatic, benzyl and indolyl thiohydroximates.
Hypothesis: UGT74C1 prefers methionine-derived over tryptophan-derived thiohydroximates.
Type: enzyme kinetics
Experiment: Profile aliphatic glucosinolates in ugt74c1 and ugt74b1 ugt74c1 lines under jasmonate treatment, herbivory and sulfur limitation.
Hypothesis: UGT74C1 becomes limiting for aliphatic glucosinolate synthesis under stress.
Type: genetic and metabolite profiling
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