TGG2 (THIOGLUCOSIDE GLUCOHYDROLASE 2, BGLU37; At5g25980) is one of the two classical shoot myrosinases of Arabidopsis, 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. TGG2 is encoded next to TGG1 in an inverted tandem arrangement and is expressed in myrosin idioblasts associated with the phloem, where the signal-peptide-bearing glycoprotein is stored in vacuole-derived compartments separated from glucosinolates until tissue damage. Its correct trafficking depends on the myrosinase-associated protein MVP1, which binds TGG2 specifically. TGG2 acts redundantly with TGG1: either enzyme alone supports normal damage-induced glucosinolate breakdown, whereas the tgg1 tgg2 double mutant lacks detectable leaf myrosinase activity, fails to hydrolyze aliphatic glucosinolates on damage and is more susceptible to generalist lepidopteran herbivores. The double mutant is also impaired in ABA- and methyl jasmonate-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: TGG2 (At5g25980) was identified in the proteome of purified vegetative vacuoles from rosette-leaf protoplasts. Reason: Consistent with storage of myrosinase in vacuole-derived compartments of myrosin idioblasts, where TGG2 is expressed, and with its signal-peptide-directed secretory-pathway biogenesis. The vacuolar proteome authors explicitly list the myrosinase gene products. Physiologically relevant storage compartment keeping the enzyme separated from glucosinolates. 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) |
| 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 Trichoplusia ni and Manduca sexta. Reason: TGG2 acts redundantly with TGG1 in producing the defensive glucosinolate hydrolysis products; the enzyme performs the hydrolytic step, satisfying participation. Core biological role of the glucosinolate-myrosinase system. 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:16640593 In Arabidopsis and other Brassicaceae, the enzyme myrosinase (beta-thioglucoside glucohydrolase, TGG) degrades glucosinolates to produce toxins that deter herbivory. |
| 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:0005777 peroxisome | HDA PMID:17951448 Proteome analysis of Arabidopsis leaf peroxisomes reveals no... | KEEP AS NON CORE | Summary: TGG2 was identified in the proteome of highly purified leaf peroxisomes and was upregulated in peroxisomes from senescent plants. Reason: TGG2 lacks a peroxisomal targeting signal and is a glycosylated secretory-pathway protein; the authors performed a control arguing against co-purification and proposed an ER-derived import route. The observation is experimental but not corroborated by targeted localization, so it is kept as non-core. Supporting Evidence: PMID:17951448 the myrosinase homolog thioglucoside glucohydrolase 2 (TGG2; At5g25980; Barth and Jander, 2006 ). All three defense-related enzymes were apparently upregulated in leaf peroxisomes isolated from senescent plants PMID:17951448 none of the defense-related proteins (BGL1, TGG2, PYK10, or ESM1) were detected by Coomassie staining |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro GH1 family (IPR001360) mapping to carbohydrate metabolic process. Reason: The physiological substrates of TGG2 are glucosinolates (thioglucosides); 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 node (PTN000039458). Reason: TGG2 is within the GH1 clade, and its closest paralog TGG1 (and root myrosinases TGG4/TGG5) retain weak O-beta-glucosidase activity, so the inherited activity is plausible. Myrosinases are nonetheless specialized S-glycosidases whose physiological substrates are glucosinolates; the O-glucosidase activity is residual and non-core. No direct O-glucosidase assay of TGG2 is available. Supporting Evidence: PMID:19703694 All myrosinases also displayed O-beta-glucosidase activity, although with lower efficiency compared to the myrosinase activity. |
| GO:0009506 plasmodesma | HDA PMID:21533090 Arabidopsis plasmodesmal proteome. | KEEP AS NON CORE | Summary: Detected in the plasmodesmal proteome of Arabidopsis suspension cells. Reason: The authors note that ~35% of the plasmodesmal proteome are putative cytoplasmic contaminants; a soluble vacuolar myrosinase has no known plasmodesmal role. Kept as a non-core, weakly supported location. Supporting Evidence: PMID:21533090 but still has a significant number (35%) of putative cytoplasmic contaminants, probably reflecting the sensitivity of the proteomic detection system |
| 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 AT5G25980 (TGG2) "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 TGG2 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: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, while tgg2-1 single mutants responded normally. Reason: The phenotype is only seen in the double mutant, implying redundancy with TGG1. Reporter studies place TGG2 expression in myrosin idioblasts but not guard cells, so how TGG2 contributes to guard-cell ABA signaling is unclear (possibly a low guard-cell expression or non-cell-autonomous effect). We defer to the experimental data but keep this as non-core. 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 The other Arabidopsis myrosinase, TGG2 , is not expressed in GC by reporter gene analysis ( Barth and Jander, 2006 ). |
| GO:0010119 regulation of stomatal movement | IMP PMID:19433491 Myrosinases, TGG1 and TGG2, redundantly function in ABA and ... | KEEP AS NON CORE | Summary: tgg1 tgg2 double mutants fail to close stomata in response to ABA, MeJA and H2O2. Reason: Reproducible double-mutant phenotype (ABA, MeJA, acrolein, allyl isothiocyanate), but TGG2 is predominantly a myrosin-idioblast myrosinase, was not detected in the guard cell proteome, and is reported absent from guard cells by reporter analysis. The stomatal role is well supported for TGG1; for TGG2 it is retained as a non-core, redundancy-dependent role. 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 Unlike TGG1, TGG2 was not found in any of the gel-based |
| GO:0019137 thioglucosidase activity | IEA GO_REF:0000003 | ACCEPT | Summary: EC 3.2.1.147 (thioglucosidase) mapping. Reason: Correct; TGG2 alone supports wild-type levels of leaf glucosinolate breakdown in tgg1 single mutants, demonstrating its myrosinase activity. 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. |
| GO:0019137 thioglucosidase activity | IMP PMID:16640593 Arabidopsis myrosinases TGG1 and TGG2 have redundant functio... | ACCEPT | Summary: tgg1 tgg2 double mutant leaf extracts have undetectable myrosinase activity, while tgg1 single mutants (TGG2 only) show wild-type glucosinolate breakdown. Reason: Genetic evidence that TGG2 is a functional myrosinase sufficient for leaf glucosinolate breakdown in the absence of TGG1; core molecular function. 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. In contrast, leaf extracts of tgg1tgg2 double mutants had undetectable myrosinase activity in vitro |
| GO:0019137 thioglucosidase activity | TAS PMID:7766881 The myrosinase gene family in Arabidopsis thaliana: gene org... | ACCEPT | Summary: Author statement from the cloning of the Arabidopsis myrosinase genes TGG1 and TGG2. Reason: Correct; confirmed by subsequent genetic evidence (IMP). Supporting Evidence: PMID:7766881 These genes were isolated from a genomic library and two of them, TGG1 and TGG2, were sequenced. |
| GO:0019762 glucosinolate catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation of glucosinolate catabolic process from the myrosinase node (PTN004151533), grounded in TGG1 and TGG2 experimental annotations. Reason: Sound phylogenetic inference; TGG2 among its own donors reflects 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. Reason: TGG2 catalyzes, redundantly with TGG1, the hydrolytic step of glucosinolate breakdown; core process. 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 | NAS PMID:7766881 The myrosinase gene family in Arabidopsis thaliana: gene org... | ACCEPT | Summary: Author statement that TGG genes encode myrosinases that degrade glucosinolates. Reason: Consistent with the experimental IMP evidence. Supporting Evidence: PMID:7766881 In situ hybridization experiments showed that TGG1 and TGG2 expressing cells are present in leaf, sepal, petal, and gynoecium. |
| 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. TGG2 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: TGG2 detected in the apoplast proteome of oxidatively stressed plants. 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; not contradicted by secretory-pathway biogenesis but without targeted support. 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: How does TGG2 contribute to ABA- and MeJA-induced stomatal closure if it is not detectably expressed in guard cells - low guard-cell expression, a non-cell-autonomous effect, or indirect effects of altered glucosinolate levels in the double mutant?
Q: Do TGG1 and TGG2 differ in substrate preference, ascorbate activation or complex formation with myrosinase-associated/binding proteins (e.g. MVP1) in a way that shapes hydrolysis product profiles?
Experiment: Express and purify recombinant TGG2 and compare its kinetics on aliphatic, indole and benzyl glucosinolates, ascorbate activation and O-beta-glucosidase activity with TGG1.
Experiment: Use cell-type-specific complementation of tgg1 tgg2 (TGG2 under a guard-cell versus a myrosin-idioblast promoter) to test where TGG2 must act to restore stomatal responses and herbivore resistance.
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