TGG1 (THIOGLUCOSIDE GLUCOHYDROLASE 1, BGLU38; At5g26000) is one of the two classical myrosinases of Arabidopsis shoots, a glycoside hydrolase family 1 beta-thioglucosidase (EC 3.2.1.147) that hydrolyzes the thioglucosidic bond of glucosinolates, releasing glucose and an unstable aglucone that rearranges to isothiocyanates or, with specifier proteins, to nitriles, epithionitriles or thiocyanates. Like other myrosinases it lacks the catalytic acid/base glutamate of O-glucosidases, and it retains only weak O-beta-glucosidase activity. It is a signal-peptide-bearing glycoprotein stored in vacuole-derived compartments of phloem-associated myrosin idioblasts and in guard cells, spatially separated from its glucosinolate substrates, so that hydrolysis occurs on tissue damage (the "mustard oil bomb"). TGG1 acts redundantly with TGG2: the double mutant lacks detectable leaf myrosinase activity and damage-induced breakdown of aliphatic glucosinolates, and is more susceptible to generalist lepidopteran herbivores. TGG1 is also one of the most abundant proteins of guard cells, where TGG1 and TGG2 are required, by an as yet undefined mechanism, for ABA-, methyl jasmonate- and isothiocyanate-induced stomatal closure.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000325 plant-type vacuole | HDA PMID:15539469 The vegetative vacuole proteome of Arabidopsis thaliana reve... | ACCEPT | Summary: TGG1 (At5g26000) was identified in the proteome of purified vegetative vacuoles from rosette-leaf protoplasts. Reason: Consistent with the known storage of myrosinase in vacuole-derived myrosin grains of myrosin cells and with the signal-peptide-directed, N-glycosylated secretory-pathway biogenesis of the enzyme; UniProt also annotates a vacuolar location. The vacuolar proteome authors explicitly list the myrosinase gene products. This is the physiologically relevant storage compartment that keeps the enzyme separated from its glucosinolate substrates until tissue damage. Supporting Evidence: PMID:15539469 we also identified five additional MAP gene products (At1g54000, At1g54010, At1g54020, At1g54030, and At1g14220) and the corresponding myrosinase gene products (At5g25980 and At5g2600) PMID:11950967 Our results suggest a cellular separation of myrosinase enzyme and glucosinolate substrate, and that myrosinase is contained in distinct cells. |
| GO:0002213 defense response to insect | IMP PMID:16640593 Arabidopsis myrosinases TGG1 and TGG2 have redundant functio... | ACCEPT | Summary: tgg1 tgg2 double mutants lacking myrosinase activity supported increased weight gain of the generalist Trichoplusia ni and of Manduca sexta. Reason: Myrosinase-dependent hydrolysis of glucosinolates releases isothiocyanates and other toxic products; this is the defining biological role of the glucosinolate-myrosinase ("mustard oil bomb") system. TGG1 acts redundantly with TGG2, so the phenotype is seen in the double mutant. TGG1 does the enzymatic work that generates the defensive products, satisfying participation. Supporting Evidence: PMID:16640593 Weight gain of two Lepidoptera, the generalist Trichoplusia ni and the facultative Solanaceae-specialist Manduca sexta, was significantly increased on tgg1tgg2 double mutants. |
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000120 | MODIFY | Summary: The supported O-glycoside hydrolase activity is beta-glucosidase activity. Reason: Refine the O-glycoside hydrolase term to beta-glucosidase activity already present. The principal thioglucosidase reaction cleaves an S-glycosidic bond and is not used as an O-glycoside descendant. O-beta-glucoside hydrolysis is directly measured for TGG1 and retained as an inferred secondary activity for TGG2. Proposed replacements: beta-glucosidase activity Supporting Evidence: PMID:19703694 All myrosinases also displayed O-beta-glucosidase activity, although with lower efficiency compared to the myrosinase activity. |
| GO:0005576 extracellular region | ISM GO_REF:0000122 | MODIFY | Summary: Refine the general extracellular assignment to the experimentally annotated apoplast context. Reason: The apoplast HDA assignment is retained elsewhere in this review as a context-dependent non-core location. That supported extracellular descendant also entails the broad term, irrespective of its prediction source. Refine to apoplast rather than treating the broad location as false; this does not replace the better-characterized intracellular storage location. Proposed replacements: apoplast Supporting Evidence: PMID:18538804 it was possible to show differential protein expression in the apoplast of plants submitted to oxidative stress |
| GO:0005773 vacuole | IEA GO_REF:0000044 | MODIFY | Summary: TGG1 is stored in plant vacuolar compartments. Reason: Refine general vacuole to plant-type vacuole, consistent with its secretory-pathway maturation and myrosin-cell storage. Proposed replacements: plant-type vacuole Supporting Evidence: PMID:15539469 the corresponding myrosinase gene products (At5g25980 and At5g2600) |
| GO:0005777 peroxisome | HDA PMID:17951448 Proteome analysis of Arabidopsis leaf peroxisomes reveals no... | KEEP AS NON CORE | Summary: Myrosinases were detected in the proteome of highly purified leaf peroxisomes. Reason: TGG1 lacks a peroxisomal targeting signal, is an extremely abundant protein, and is a glycosylated secretory-pathway protein; the authors themselves proposed an ER-derived route and a defense role, and control experiments argued against co-purification. The observation is experimental and cannot be dismissed, but it is not corroborated by targeted localization of TGG1, so it is kept as a non-core location. Supporting Evidence: PMID:17951448 Seven proteins, including beta-glucosidases and myrosinases, support the currently emerging evidence for an important role of leaf peroxisomes in defense against pathogens and herbivores. PMID:17951448 Specific soluble proteins, for instance, those that are glycosylated as they pass the ER, as are PYK10 and myrosinases ( Halkier and Gershenzon, 2006 ), may thus enter the peroxisomal matrix also via the ER |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro GH1 family (IPR001360) mapping to carbohydrate metabolic process. Reason: The glycosyl hydrolase family 1 mapping assumes O-glycoside (carbohydrate) substrates. The physiological substrates of TGG1 are glucosinolates (thioglucosides), and glucosinolate catabolic process (GO:0019762) is not a descendant of carbohydrate metabolic process. Replace with the specific, experimentally supported process. Proposed replacements: glucosinolate catabolic process Supporting Evidence: PMID:16640593 leaf extracts of tgg1tgg2 double mutants had undetectable myrosinase activity in vitro, and damage-induced breakdown of endogenous glucosinolates was apparently absent for aliphatic and greatly slowed for indole glucosinolates |
| GO:0008422 beta-glucosidase activity | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT propagation of beta-glucosidase activity from the GH1 beta-glucosidase node (PTN000039458) to the myrosinase subclade. Reason: The GH1 ancestral O-beta-glucosidase activity is retained at low efficiency by TGG1 (Km of 34 mM for p-nitrophenyl beta-D-glucoside versus 45 uM for sinigrin, per UniProt), so the IBA is not wrong, and TGG1 is within the clade. However, myrosinases are specialized S-glycosidases whose physiological substrates are glucosinolates, so O-beta-glucosidase activity is a residual, non-core activity. Supporting Evidence: PMID:19703694 All myrosinases also displayed O-beta-glucosidase activity, although with lower efficiency compared to the myrosinase activity. |
| GO:0008422 beta-glucosidase activity | IDA PMID:19703694 Myrosinases from root and leaves of Arabidopsis thaliana hav... | KEEP AS NON CORE | Summary: Recombinant TGG1 expressed in Pichia pastoris hydrolyzed an O-beta-glucoside (p-nitrophenyl beta-D-glucoside) with lower efficiency than sinigrin. Reason: Directly demonstrated but with a millimolar Km on an artificial substrate; no physiological O-glucoside substrate is known. Retained as a real but non-core activity. Supporting Evidence: PMID:19703694 All myrosinases also displayed O-beta-glucosidase activity, although with lower efficiency compared to the myrosinase activity. |
| GO:0008422 beta-glucosidase activity | IEA GO_REF:0000003 | KEEP AS NON CORE | Summary: EC 3.2.1.21 (beta-glucosidase) mapping from the UniProt catalytic activity record, which is based on the IDA data of PMID:19703694. Reason: Consistent with the experimentally observed weak O-beta-glucosidase activity; non-core relative to thioglucosidase activity. Supporting Evidence: PMID:19703694 All myrosinases also displayed O-beta-glucosidase activity |
| GO:0009507 chloroplast | HDA PMID:18431481 Sorting signals, N-terminal modifications and abundance of t... | MARK AS OVER ANNOTATED | Summary: The source study explicitly classifies this detected protein as non-plastid. Reason: PMID:18431481 distinguishes MS detection from its curated chloroplast assignment. The publisher supplemental abundance workbook (journal.pone.0001994.s003) and annotated-protein workbook (s005) explicitly label AT5G26000 (TGG1) "not plastid"; the exact files and row identities are recorded in the gene notes. Thus the chloroplast annotation overinterprets detection contrary to the authors' own target-specific classification. This conclusion does not rest merely on absence of a predicted transit peptide, and it does not deny the peptide identifications. Supporting Evidence: PMID:18431481 30 proteins were considered non-plastid contaminations (Table S4). |
| GO:0009536 plastid | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | MARK AS OVER ANNOTATED | Summary: The microsome experiment does not independently establish plastid 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 TGG1 specifically to plastid 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:0009579 thylakoid | HDA PMID:16648217 High light response of the thylakoid proteome in arabidopsis... | MARK AS OVER ANNOTATED | Summary: Thylakoid-fraction detection does not outweigh the later target-specific non-plastid classification. Reason: The full text of PMID:16648217 was recovered and read: it is a two-dimensional-gel/MS analysis of soluble thylakoid preparations, not target-specific imaging of TGG1. More decisively, the later chloroplast proteome study PMID:18431481 explicitly classifies AT5G26000/TGG1 as "not plastid" in its annotated-protein and abundance supplements, despite detecting its peptides. Together with independent vacuolar localization, this supports marking a thylakoid-resident assignment as over-annotated while preserving the observed fraction detection. It does not establish a wrong-gene citation. Supporting Evidence: PMID:16648217 The soluble thylakoid proteomes of wild type and vtc2-2 were compared after 0, 1, 3, and 5 d of HL using two-dimensional gels PMID:18431481 30 proteins were considered non-plastid contaminations (Table S4). |
| GO:0009625 response to insect | IEP PMID:23144921 Water stress and aphid feeding differentially influence meta... | KEEP AS NON CORE | Summary: TGG1 transcript was down-regulated by feeding of the aphids Myzus persicae and Brevicoryne brassicae. Reason: Expression-level response only; aphids largely avoid the myrosinase system and myrosinase mutations do not affect aphid reproduction. The observation is valid as a transcriptional response but does not represent a core function. Supporting Evidence: PMID:23144921 One gene encoding for myrosinase1 in A. thaliana, TGG1, was included in our study. Water stress did not change its expression levels, but plant infestation with M. persicae or B. brassicae down-regulated TGG1 in all treatments. PMID:16640593 Reproduction of two Homoptera, Myzus persicae and Brevicoryne brassicae, was unaffected by myrosinase mutations. |
| GO:0009737 response to abscisic acid | IMP PMID:19433491 Myrosinases, TGG1 and TGG2, redundantly function in ABA and ... | KEEP AS NON CORE | Summary: ABA failed to induce stomatal closure in tgg1-3 tgg2-1 double mutants; tgg1 single mutants were also hyposensitive to ABA inhibition of guard cell inward K+ channels. Reason: Reproducible genetic evidence (Islam et al. 2009; Zhao et al. 2008; Islam et al. 2020) places TGG1 in guard-cell ABA signaling, downstream of ROS and upstream of cytosolic Ca2+ elevation. The mechanism (catalytic or not) is unknown, and this is a secondary role relative to the defensive glucosinolate hydrolysis; kept as non-core. The more specific stomatal-movement annotation captures the physiological output. Supporting Evidence: PMID:19433491 ABA, MeJA and H(2)O(2) induced stomatal closure in wild type, tgg1-3 and tgg2-1, but failed to induce stomatal closure in tgg1-3 tgg2-1. PMID:19114538 tgg1 mutants were hyposensitive to abscisic acid (ABA) inhibition of guard cell inward K(+) channels and stomatal opening |
| GO:0010119 regulation of stomatal movement | IMP PMID:19433491 Myrosinases, TGG1 and TGG2, redundantly function in ABA and ... | ACCEPT | Summary: tgg1 tgg2 double mutants fail to close stomata in response to ABA, MeJA and H2O2, while Ca2+-induced closure is intact. Reason: TGG1 is strikingly abundant in guard cells, and the stomatal phenotype has been reproduced in several independent studies (ABA, MeJA, acrolein, allyl isothiocyanate), with overexpression of a Brassica TGG1 accelerating pathogen-induced stomatal closure. This is a well-supported secondary biological role of TGG1, although the molecular mechanism remains unresolved. Supporting Evidence: PMID:19433491 A model is discussed in which two myrosinases redundantly function downstream of ROS production and upstream of cytosolic Ca(2+) elevation in ABA and MeJA signaling in guard cells. PMID:19114538 THIOGLUCOSIDE GLUCOHYDROLASE1 (TGG1), a myrosinase that catalyzes the production of toxic isothiocyanates from glucosinolates, showed striking abundance in the guard cell proteome. PMID:39894892 Allyl isothiocyanate at 50 ΞΌM and 100 ΞΌM induced stomatal closure in the tgg1 and tgg2 single mutants but not in the tgg1 tgg2 double mutant. |
| GO:0019137 thioglucosidase activity | IDA PMID:15643972 Nucleotide variation at the myrosinase-encoding locus, TGG1,... | ACCEPT | Summary: Myrosinase activity was quantified across Arabidopsis accessions in a study of TGG1 nucleotide variation. Reason: TGG1 is an established thioglucosidase (myrosinase). The cached abstract reports accession-level activity without association to TGG1 alleles; we defer to the curator, and the activity is independently demonstrated with recombinant TGG1 (PMID:19703694). Supporting Evidence: PMID:15643972 The Arabidopsis thaliana TGG1 gene encodes thioglucoside glucohydrolase (myrosinase), an enzyme catalysing the hydrolysis of glucosinolate compounds. |
| GO:0019137 thioglucosidase activity | IDA PMID:19703694 Myrosinases from root and leaves of Arabidopsis thaliana hav... | ACCEPT | Summary: Recombinant His-tagged TGG1 purified from Pichia pastoris hydrolyzed sinigrin (allyl glucosinolate). Reason: Direct biochemical demonstration of thioglucosidase (myrosinase, EC 3.2.1.147) activity with purified enzyme; core molecular function. Supporting Evidence: PMID:19703694 Myrosinase activity was confirmed for all forms and compared with respect to catalytic activity towards the allyl-glucosinolate sinigrin. |
| GO:0019137 thioglucosidase activity | IEA GO_REF:0000003 | ACCEPT | Summary: EC 3.2.1.147 (thioglucosidase) mapping. Reason: Correct; matches the experimentally demonstrated core activity. Supporting Evidence: PMID:19703694 Myrosinases (EC 3.2.1.147) are beta-thioglucoside glucosidases present in Brassicaceae plants. |
| GO:0019137 thioglucosidase activity | IMP PMID:16640593 Arabidopsis myrosinases TGG1 and TGG2 have redundant functio... | ACCEPT | Summary: Leaf extracts of tgg1 tgg2 double mutants had undetectable myrosinase activity. Reason: Genetic evidence that TGG1 (with TGG2) accounts for essentially all leaf myrosinase activity; core function. Supporting Evidence: PMID:16640593 leaf extracts of tgg1tgg2 double mutants had undetectable myrosinase activity in vitro |
| GO:0019137 thioglucosidase activity | ISS PMID:7766881 The myrosinase gene family in Arabidopsis thaliana: gene org... | ACCEPT | Summary: Sequence-similarity inference of myrosinase activity from Brassica myrosinases at the time the Arabidopsis TGG genes were cloned. Reason: Historical ISS assertion, since confirmed experimentally (IDA, IMP). Correct. Supporting Evidence: PMID:7766881 Southern blot analysis showed that Arabidopsis thaliana contains three myrosinase genes. |
| GO:0019762 glucosinolate catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation of glucosinolate catabolic process from the myrosinase node (PTN004151533), based on the experimental annotations of TGG1 (AT5G26000) and TGG2 (AT5G25980). Reason: Sound phylogenetic inference; TGG1 appearing among the donors reflects its own experimental grounding and is not circular. Supporting Evidence: PMID:16640593 damage-induced breakdown of endogenous glucosinolates was apparently absent for aliphatic and greatly slowed for indole glucosinolates |
| GO:0019762 glucosinolate catabolic process | IMP PMID:16640593 Arabidopsis myrosinases TGG1 and TGG2 have redundant functio... | ACCEPT | Summary: Damage-induced glucosinolate breakdown is absent (aliphatic) or greatly slowed (indole) in tgg1 tgg2 double mutants, and maturing leaves accumulate more glucosinolate. Reason: TGG1 catalyzes the hydrolytic step of glucosinolate breakdown; core process. Note that developmental glucosinolate turnover during senescence and germination is independent of TGG1/TGG2. Supporting Evidence: PMID:16640593 Glucosinolate breakdown in crushed leaves of tgg1 or tgg2 single mutants was comparable to that of wild-type, indicating redundant enzyme function. PMID:16640593 damage-induced breakdown of endogenous glucosinolates was apparently absent for aliphatic and greatly slowed for indole glucosinolates |
| GO:0019762 glucosinolate catabolic process | NAS PMID:7766881 The myrosinase gene family in Arabidopsis thaliana: gene org... | ACCEPT | Summary: Author statement that the cloned TGG genes encode myrosinases, which degrade glucosinolates. Reason: Consistent with, and superseded by, the experimental IMP evidence. Supporting Evidence: PMID:7766881 Myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1.) is in Brassicaceae species such as Brassica napus and Sinapis alba encoded by two differentially expressed gene families |
| GO:0022626 cytosolic ribosome | HDA PMID:15821981 High heterogeneity within the ribosomal proteins of the Arab... | MARK AS OVER ANNOTATED | Summary: Co-migration with ribosomes does not establish a cytosolic ribosome component. Reason: PMID:15821981 explicitly describes non-ribosomal proteins that co-migrate with 80S particles and calls their association a possibility for further investigation. TGG1 is a secretory-pathway myrosinase with independent vacuolar localization evidence, so co-sedimentation alone does not establish its residence in the cytosolic ribosome. Retain the detection but mark the component assignment as over-annotated. The publication cache remains abstract-only after a fresh fetch; the quoted methodological caveat is accessible and sufficient for this limited assessment, not for claiming a gene misidentification or REMOVE. Supporting Evidence: PMID:15821981 In addition, we have identified a number of non-ribosomal proteins that co-migrate with the plant 80S ribosomes during gradient centrifugation suggesting their possible association with the 80S ribosomes. |
| GO:0048046 apoplast | HDA PMID:18538804 Hydroponic isotope labelling of entire plants (HILEP) for qu... | KEEP AS NON CORE | Summary: TGG1 detected in the apoplast proteome of oxidatively stressed plants (HILEP quantitative proteomics). Reason: Retain the curated experimental apoplast-proteomics observation as a context-dependent non-core location. Intracellular myrosin-cell storage is the better-characterized main localization, but it does not invalidate this separately observed extracellular pool. Supporting Evidence: PMID:18538804 it was possible to show differential protein expression in the apoplast of plants submitted to oxidative stress |
| GO:0099503 secretory vesicle | HDA PMID:25293756 A proteomic strategy for global analysis of plant protein co... | KEEP AS NON CORE | Summary: Detected in a size-exclusion chromatography proteomic survey of leaf protein complexes. Reason: High-throughput fractionation data; a secretory-pathway compartment is compatible with myrosinase biogenesis, but there is no targeted evidence for secretory vesicles. Kept as non-core. Supporting Evidence: PMID:25293756 Applying this approach to the crude cytosolic fraction of Arabidopsis thaliana leaves using size exclusion chromatography, we identified hundreds of cytosolic proteins that appeared to exist as components of stable protein complexes. |
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Download this section (compressed HTML)Q: Does the guard-cell role of TGG1 in ABA/MeJA/isothiocyanate-induced stomatal closure require its thioglucosidase activity, and if so which glucosinolate pool is hydrolyzed in intact guard cells, or does TGG1 act non-catalytically?
Q: How is TGG1 retained in vacuole-derived myrosin grains, and what triggers its release upon tissue damage versus in guard-cell signaling?
Q: Do the proteomics-derived plastid, thylakoid, ribosome and peroxisome localizations of TGG1 reflect genuine minor pools or contamination by an extremely abundant protein?
Experiment: Complement tgg1 tgg2 double mutants with catalytically inactive TGG1 (nucleophile Glu mutant) versus wild-type TGG1 under the guard-cell TGG1 promoter and test ABA-, MeJA- and AITC-induced stomatal closure.
Experiment: Use native-promoter TGG1-fluorescent protein fusions with organelle markers and immunogold EM to test the peroxisomal and apoplastic pools reported by proteomics.
Experiment: Profile glucosinolate hydrolysis products in isolated guard cells of wild type and tgg mutants after ABA treatment to test whether stomatal signaling involves in situ glucosinolate hydrolysis.
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