A0A2I4G8T1 is a UDP-glycosyltransferase from Juglans regia (English walnut), belonging to the UGT73C subfamily based on PANTHER classification (PTHR48047:SF229, UDP-GLYCOSYLTRANSFERASE 73C3-RELATED). The 488-amino-acid protein contains a GT1_Gtf-like catalytic domain and a C-terminal UDP-glycosyltransferase signature motif (UDPGT/Pfam PF00201), along with an N-terminal glycosyltransferase domain (Pfam PF26168). As a GT1 family glycosyltransferase, it catalyzes the transfer of sugar moieties from UDP-sugar donors to small-molecule acceptors. In plants, UGT73C family members are known to glycosylate diverse substrates including brassinosteroids, cytokinins, flavonoids, and other phenolic compounds, thereby modulating hormone homeostasis and secondary metabolism. The protein is encoded on chromosome 3 and its function is inferred entirely from homology, with no direct experimental characterization reported.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0035251
UDP-glucosyltransferase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: This IBA annotation is derived from phylogenetic inference (PANTHER) based on orthology to six Arabidopsis UDP-glucosyltransferases (AT1G73880/UGT73C3, AT2G36750, AT2G36790, AT2G36800, AT3G53160, AT5G03490). The protein contains all expected domains (GT1_Gtf-like catalytic domain, UDPGT Pfam domain, UDP-glycosyltransferase signature) and is classified in PANTHER subfamily SF229 (UDP-GLYCOSYLTRANSFERASE 73C3-RELATED). UDP-glucosyltransferase activity (GO:0035251) is more specific than the parent term UDP-glycosyltransferase activity, specifying glucose as the sugar donor. This is well supported by the phylogenetic context.
Reason: The phylogenetic placement with multiple Arabidopsis UGT73 family members, combined with domain architecture (GT1_Gtf-like, UDPGT, UDP_glycos_trans_CS), strongly supports UDP-glucosyltransferase activity. This is the most specific and informative annotation among the three.
|
|
GO:0008194
UDP-glycosyltransferase activity
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: This IEA annotation comes from the InterPro domain IPR002213 (UDP-glucosyltransferase), which is present in the protein. The annotation to GO:0008194 (UDP-glycosyltransferase activity) is correct but is a parent term of the more specific GO:0035251 (UDP-glucosyltransferase activity) already assigned by IBA. It is redundant given the more specific annotation.
Reason: This is a true parent term of GO:0035251. The protein does have UDP-glycosyltransferase activity, but the more specific UDP-glucosyltransferase activity better captures its function. Keeping as non-core since it is correct but less informative.
|
|
GO:0016757
glycosyltransferase activity
|
IEA
GO_REF:0000117 |
MARK AS OVER ANNOTATED |
Summary: This IEA annotation from ARBA assigns the very broad parent term glycosyltransferase activity (GO:0016757). While correct, this is overly general given that more specific terms (GO:0035251, GO:0008194) are already assigned. GO:0016757 encompasses all glycosyltransferases regardless of donor substrate, while this protein clearly belongs to the UDP-dependent GT1 family.
Reason: This is the broadest of the three molecular function annotations and adds no information beyond what is captured by the more specific terms. The protein's domain architecture and phylogenetic placement clearly place it in the UDP-glycosyltransferase family, making this overly general annotation uninformative.
|
Q: What are the in vivo acceptor substrates of this UGT73C-related glucosyltransferase in Juglans regia? Walnut produces abundant naphthoquinones (e.g. juglone) and phenolics that could be glycosylation targets.
Q: Does this enzyme glycosylate juglone (5-hydroxy-1,4-naphthoquinone), the characteristic allelochemical of walnut, potentially serving a detoxification or storage role?
Experiment: In vitro substrate screening of recombinant A0A2I4G8T1 with UDP-glucose and candidate acceptors including juglone, quercetin, kaempferol, brassinolide, and trans-zeatin to determine substrate specificity.
Hypothesis: Given its UGT73C subfamily classification and the prominence of juglone in walnut metabolism, the enzyme may glycosylate juglone or related naphthoquinones as a detoxification mechanism.
Experiment: Expression profiling of LOC109005703 across walnut tissues (leaves, roots, hull, bark) and developmental stages to identify where glycosylation activity is most needed.
Hypothesis: Expression may be highest in tissues with active secondary metabolism or juglone production, suggesting a role in phenolic compound homeostasis.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
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We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
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LOC109005703 encodes a glycosyltransferase belonging to the UDP-glycosyltransferase (UGT) superfamily in English walnut (Juglans regia). While no direct experimental studies on this specific gene were identified in the literature, comprehensive functional annotation can be inferred from its conserved domain architecture, family membership, and characterized homologs in walnut and related plant species. This report synthesizes current knowledge to provide a detailed functional annotation addressing catalytic mechanism, substrate specificity, pathway involvement, and subcellular localization.
The gene LOC109005703 (UniProt accession A0A2I4G8T1) from Juglans regia encodes a protein annotated as a glycosyltransferase with the enzyme classification EC 2.4.1.- (tahara2024elucidationandreconstitution pages 2-4). The protein belongs to the UDP-glycosyltransferase family, which represents the largest glycosyltransferase superfamily in plants (speeckaert2022ugt72amajor pages 1-2). In the model plant Arabidopsis thaliana, this family comprises 123 members, while in the tree species Populus trichocarpa, it has expanded to 281 members (speeckaert2022ugt72amajor pages 2-5). This expansion reflects the diversification of specialized metabolism in plants, particularly in long-lived woody species like walnut (speeckaert2022ugt72amajor pages 2-5).
LOC109005703 contains two critical functional domains characteristic of plant UGTs:
UDPGT domain (PF00201): The C-terminal domain responsible for binding the UDP-sugar donor molecule (gharabli2024thesugardonor pages 1-3, speeckaert2020characterizationofthe pages 1-4). This domain contains the highly conserved Plant Secondary Product Glycosyltransferase (PSPG) box, a 44-amino acid motif essential for UDP-sugar recognition (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4, speeckaert2022ugt72amajor pages 2-5).
Glyco_transf_N domain (PF26168, IPR058980): The N-terminal domain that binds and recognizes the acceptor substrate molecule (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4). This domain is more variable among UGT family members and largely determines substrate specificity (speeckaert2022ugt72amajor pages 2-5).
Plant UGTs adopt a canonical GT-B fold consisting of two Rossmann-type domains connected by a linker region, forming a central catalytic cleft (gharabli2024thesugardonor pages 1-3, speeckaert2022ugt72amajor pages 2-5). The C-terminal domain containing the PSPG motif predominantly interacts with the UDP-sugar donor, while the N-terminal domain forms a more variable pocket that accommodates diverse acceptor molecules (gharabli2024thesugardonor pages 3-4, speeckaert2022ugt72amajor pages 2-5). Within the PSPG box, conserved residues at specific positions interact with the UDP moiety and sugar portion of the donor substrate, with the terminal glutamine (Gln) residue often playing a critical role in sugar donor specificity (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4).
UGTs catalyze the transfer of a sugar moiety from a UDP-activated sugar donor to a wide variety of acceptor molecules through glycosylation reactions (gharabli2024thesugardonor pages 1-3). The enzyme performs regio- and stereoselective one-step glycosylation, making these enzymes valuable tools in both plant metabolism and biotechnological applications (gharabli2024thesugardonor pages 1-3).
The catalytic mechanism of plant family 1 UGTs involves a highly conserved catalytic dyad, typically comprising histidine (His) and aspartate (Asp) residues (gharabli2024thesugardonor pages 1-3). In O-glycosylation reactions, the His residue acts as a BrΓΈnsted base that deprotonates the hydroxyl group of the acceptor molecule, facilitating nucleophilic attack on the anomeric carbon of the UDP-sugar (gharabli2024thesugardonor pages 1-3, speeckaert2022ugt72amajor pages 2-5). This reaction proceeds via an SN2-like mechanism with inversion of the anomeric configuration (gharabli2024thesugardonor pages 1-3).
Plant UGTs most commonly utilize UDP-glucose (UDP-Glc) as the sugar donor, though members of the superfamily can also accept UDP-galactose (UDP-Gal), UDP-glucuronic acid (UDP-GlcA), UDP-rhamnose (UDP-Rha), and UDP-xylose (UDP-Xyl) depending on subfamily-specific donor recognition determinants (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4). The donor specificity is strongly influenced by residues within and near the PSPG motif, particularly at conserved positions that interact with the C4 and C6 hydroxyl groups of the sugar moiety (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4). While the specific sugar donor preference of LOC109005703 cannot be determined without experimental characterization, UDP-glucose is the most likely primary substrate based on family-wide trends (gharabli2024thesugardonor pages 1-3).
While the precise acceptor substrate for LOC109005703 remains unknown without direct experimental evidence, the protein is predicted to act on phenolic secondary metabolites based on family characteristics and the metabolic context of walnut. Plant UGTs broadly glycosylate specialized metabolites derived from the phenylpropanoid pathway, including:
Flavonoids: UGTs catalyze the glycosylation of various flavonoid classes including anthocyanins, flavonols (quercetin, kaempferol), and flavones (ren2022genomewideanalysisof pages 2-4, ren2022genomewideanalysisof pages 1-2, speeckaert2022ugt72amajor pages 1-2). In the related species Morella rubra (Chinese bayberry), characterized UGTs such as MrUFGT (MrUGT78A26) and MrUGT72B67 were identified as flavonoid 3-O-glucosyltransferases involved in the accumulation of cyanidin 3-O-glucoside and quercetin 3-O-glucoside (ren2022genomewideanalysisof pages 2-4, ren2022genomewideanalysisof pages 1-2). The importance of a conserved glutamine residue (Gln375 in MrUFGT and Gln391 in MrUGT72B67) for glucosyl transfer activity was demonstrated through site-directed mutagenesis (ren2022genomewideanalysisof pages 2-4, ren2022genomewideanalysisof pages 1-2).
Gallic Acid and Hydroxybenzoic Acids: Members of the UGT84A clade catalyze the formation of Ξ²-glucogallin (1-O-galloyl-Ξ²-D-glucose) from gallic acid and UDP-glucose, a critical step in hydrolyzable tannin biosynthesis (tahara2024elucidationandreconstitution pages 1-2, tahara2024elucidationandreconstitution pages 4-6). In walnut, two characterized enzymes, JrGGT1 (UGT84A73) and JrGGT2 (UGT84A74), have been identified as gallic acid glucosyltransferases (tahara2024elucidationandreconstitution pages 4-6). These enzymes exhibit substrate promiscuity, accepting both hydroxybenzoic acids (HBAs; C6-C1 compounds) and hydroxycinnamic acids (HCAs; C6-C3 compounds) (tahara2024elucidationandreconstitution pages 4-6).
Monolignols: The UGT72 family includes members that glycosylate monolignols (p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol), producing monolignol glucosides such as coniferin and syringin (speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2, speeckaert2020characterizationofthe pages 1-4). In poplar (Populus spp.), UGT72 family members including UGT72AZ1, UGT72AZ2, UGT72B37, and UGT72B39 have been demonstrated to glycosylate monolignols in vitro (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10).
LOC109005703 functions within the broader context of plant secondary metabolism, specifically the phenylpropanoid pathway (speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2). This pathway begins with the aromatic amino acids phenylalanine and tyrosine, which are products of the shikimate pathway (speeckaert2022ugt72amajor pages 2-5). Through a series of enzymatic steps involving phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate:CoA ligase (4CL), the pathway generates p-coumaroyl-CoA, the last common precursor for the biosynthesis of monolignols, flavonoids, stilbenes, and other phenylpropanoid-derived compounds (speeckaert2022ugt72amajor pages 2-5).
Walnut is known to accumulate hydrolyzable tannins (HTs), a class of polyphenols characteristic of core eudicot plants (tahara2024elucidationandreconstitution pages 2-4, tahara2024elucidationandreconstitution pages 1-2). The biosynthesis of HTs is initiated by the formation of gallic acid from 3-dehydroshikimic acid, catalyzed by bifunctional dehydroquinate dehydratase/shikimate dehydrogenases (DQD/SDHs) (tahara2024elucidationandreconstitution pages 1-2). A DQD/SDH from Juglans regia (JrSDH) has been described that catalyzes the oxidation of 3-dehydroshikimic acid to gallic acid (tahara2024elucidationandreconstitution pages 1-2).
In the second step of HT biosynthesis, UDP-glycosyltransferases esterify gallic acid with glucose to form Ξ²-glucogallin (1-O-galloyl-Ξ²-D-glucose) (tahara2024elucidationandreconstitution pages 1-2, tahara2024elucidationandreconstitution pages 4-6). This reaction is catalyzed by gallic acid UGTs belonging to the UGT84A clade (tahara2024elucidationandreconstitution pages 4-6). Ξ²-Glucogallin then serves as both an acyl acceptor and donor in subsequent galloylation steps, eventually leading to the formation of gallotannins and ellagitannins (tahara2024elucidationandreconstitution pages 1-2, tahara2024elucidationandreconstitution pages 4-6). While LOC109005703's specific role in this pathway cannot be confirmed without experimental data, its family membership and the presence of characterized walnut gallic acid UGTs (JrGGT1 and JrGGT2) suggest a potential involvement in phenolic acid or tannin-related metabolism (tahara2024elucidationandreconstitution pages 4-6).
UGTs play essential roles in flavonoid biosynthesis by catalyzing the glycosylation of flavonoid aglycones, which enhances their solubility, stability, and biological activity (ren2022genomewideanalysisof pages 2-4, ren2022genomewideanalysisof pages 1-2, speeckaert2022ugt72amajor pages 1-2). In Chinese bayberry, UV-B treatment significantly induced the accumulation of cyanidin 3-O-glucoside and quercetin 3-O-glucoside in fruit, with corresponding increases in the expression of specific UGT genes (ren2022genomewideanalysisof pages 2-4, ren2022genomewideanalysisof pages 1-2). Given the nutritional and medical importance of flavonoid glycosides in walnut tissues, LOC109005703 may contribute to the diversification of these bioactive compounds.
UGT72 family members are involved in monolignol homeostasis through the glycosylation of monolignols, producing storage or transport forms of these lignin precursors (speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2, speeckaert2020characterizationofthe pages 1-4). Monolignol glucosides such as coniferin and syringin accumulate in vascular tissues and can be incorporated into the lignin polymer (speeckaert2020characterizationofthe pages 1-4). Glycosylation renders monolignols less cytotoxic by reducing their reactivity and facilitates their storage in vacuoles or transport to the cell wall (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10).
Glycosylation serves multiple important functions in plant metabolism (speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2):
While subcellular localization data for LOC109005703 is not available, insights can be drawn from characterized UGT family members. Studies on poplar UGT72 proteins revealed diverse localization patterns depending on subfamily membership (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10). UGT72 group 1 members (UGT72AZ1 and UGT72AZ2) and group 4 members (UGT72B37 and UGT72B39) were found to be associated with both the nucleus and the endoplasmic reticulum (ER) (speeckaert2020characterizationofthe pages 1-4). In contrast, UGT72A2 (group 2) localized to bodies associated with chloroplasts and possibly within chloroplasts themselves (speeckaert2020characterizationofthe pages 1-4).
Based on these observations and the general characteristics of UGTs involved in secondary metabolism, LOC109005703 is most likely localized to the cytoplasm and/or endoplasmic reticulum (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10). This localization would be consistent with its predicted role in glycosylating phenolic secondary metabolites. Following glycosylation, the products are often transported to and stored in vacuoles, where they accumulate at high concentrations (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10).
Expression patterns of UGT genes in woody plants often show enrichment in vascular tissues, particularly in phloem, cambium, and developing xylem (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10). Promoter analyses of poplar UGT72 genes revealed the presence of cis-regulatory elements associated with vascular tissue differentiation and secondary cell wall formation, including Secondary wall MYB-Responsive Elements (SMRE), Secondary wall NAC-Binding Elements (SNBE), and Tracheary-Element-Regulating cis-Elements (TERE) (speeckaert2020characterizationofthe pages 6-10). While tissue-specific expression data for LOC109005703 is not available, similar expression patterns would be expected given its family membership.
The functional annotation of LOC109005703 presented in this report is based on:
Important limitation: No direct experimental functional characterization or gene expression data for LOC109005703 was identified in the accessible scientific literature. Several recent publications specifically on walnut UGT gene family members and their roles in anthocyanin, polyphenol, and hydrolyzable tannin biosynthesis could not be retrieved, including genome-wide UGT family analyses by Shi et al. (2024) and transcriptomic studies by Zhao et al. (2023) and Wang et al. (2021).
The functional annotation provided represents inference-based predictions derived from:
- Conserved domain structure and family membership
- Characterized homologs in walnut and closely related plant species
- General biochemical properties of the UGT superfamily
Confidence assessment: The prediction that LOC109005703 functions as a glycosyltransferase catalyzing the transfer of a sugar from UDP-sugar to a small-molecule acceptor is highly confident based on domain structure. The prediction that it acts on phenolic secondary metabolites (flavonoids, phenolic acids, or monolignols) in the phenylpropanoid pathway is moderately confident based on family characteristics and walnut metabolism. The specific substrate identity, exact biochemical pathway, tissue expression pattern, and subcellular localization remain uncertain without direct experimental validation.
| Category | Annotation for LOC109005703 / A0A2I4G8T1 | Evidence / Basis |
|---|---|---|
| Gene / protein identity | Gene: LOC109005703; UniProt accession: A0A2I4G8T1; Organism: Juglans regia (English walnut); Protein family: UDP-glycosyltransferase family | UniProt-provided identity in the prompt; plant UGTs are a major GT1 family defined by UDP-sugar-dependent glycosylation and a conserved PSPG motif (gharabli2024thesugardonor pages 1-3, speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2) |
| Catalytic function | Enzyme class: Glycosyltransferase, EC 2.4.1.-; Predicted reaction: transfer of a sugar from a UDP-sugar donor to a small-molecule acceptor; Likely bond type: most likely O-glycosylation/ester-forming or O-glucosylation activity typical of plant family 1 UGTs | Plant family 1 UGTs transfer sugars from UDP-activated donors to diverse acceptors in a regio- and stereoselective one-step reaction (gharabli2024thesugardonor pages 1-3); related plant UGTs glycosylate phenylpropanoids, flavonoids, and hydroxybenzoic acids (speeckaert2022ugt72amajor pages 2-5, tahara2024elucidationandreconstitution pages 4-6, speeckaert2020characterizationofthe pages 1-4) |
| Catalytic mechanism | Mechanism: conserved catalytic dyad, typically His-Asp; His acts as catalytic base to deprotonate the acceptor, enabling SN2-like nucleophilic attack on the anomeric carbon of the UDP-sugar with inversion of configuration | Explicitly described for plant family 1 UGTs in structural/mechanistic review literature (gharabli2024thesugardonor pages 1-3); UGT72 structural discussion also places catalytic His near acceptor and conserved C-terminal residues near donor sugar (speeckaert2022ugt72amajor pages 2-5) |
| Sugar donor(s) | Most likely primary donor: UDP-glucose; Possible alternative donors in broader UGT family: UDP-galactose, UDP-rhamnose, UDP-glucuronic acid, UDP-xylose depending on subfamily-specific donor recognition | UDP-glucose is the most common donor for plant UGTs; donor specificity is strongly influenced by the PSPG motif and nearby residues (gharabli2024thesugardonor pages 1-3, gharabli2024thesugardonor pages 3-4) |
| Predicted acceptor substrates | Predicted acceptors: phenolic small molecules, especially flavonoids, hydroxybenzoic/hydroxycinnamic acids, gallic acid, and/or monolignols; exact substrate for LOC109005703 is unknown | Plant UGTs broadly glycosylate specialized metabolites (speeckaert2022ugt72amajor pages 1-2, speeckaert2020characterizationofthe pages 1-4); UGT84A enzymes can glycosylate gallic acid and related phenolic acids (tahara2024elucidationandreconstitution pages 4-6); UGT72 members often glycosylate monolignols and some flavonoids (speeckaert2022ugt72amajor pages 2-5, speeckaert2020characterizationofthe pages 1-4) |
| Key domains | Glyco_transf_N / PF26168: N-terminal acceptor-binding region; UDPGT / PF00201: C-terminal donor-binding domain; UDP_glycos_trans_CS / PSPG box: conserved plant secondary product glycosyltransferase motif important for UDP-sugar binding | The N-terminal domain is more variable and largely shapes acceptor recognition, whereas the conserved C-terminal PSPG-containing domain binds the UDP-sugar donor (gharabli2024thesugardonor pages 3-4, speeckaert2022ugt72amajor pages 2-5, speeckaert2020characterizationofthe pages 1-4) |
| Overall structure | Predicted fold: canonical GT-B fold with two Rossmann-like domains connected by a linker, forming a central catalytic cleft | Described for plant UGTs generally and for UGT72 family members specifically (gharabli2024thesugardonor pages 3-4, speeckaert2022ugt72amajor pages 2-5) |
| Biochemical pathways | Primary pathway context: phenylpropanoid / specialized secondary metabolism; Likely pathway interfaces: flavonoid glycosylation, hydroxybenzoic acid conjugation, monolignol homeostasis, and potentially hydrolyzable tannin-related metabolism | UGTs act extensively in phenylpropanoid and specialized metabolism (speeckaert2022ugt72amajor pages 2-5, speeckaert2022ugt72amajor pages 1-2); walnut and other core eudicots use UGTs in pathways connected to phenolics and tannins (tahara2024elucidationandreconstitution pages 2-4, tahara2024elucidationandreconstitution pages 4-6) |
| Potential role in walnut metabolism | Most plausible functional niche: modification of walnut phenolic metabolites to alter solubility, stability, storage, transport, and detoxification; could contribute to accumulation/homeostasis of flavonoid glycosides, tannin intermediates, or monolignol glucosides, but this remains unverified for this specific locus | Glycosylation generally decreases toxicity and increases solubility/stability of specialized metabolites (speeckaert2022ugt72amajor pages 1-2); walnut is rich in polyphenol-related metabolism and known walnut UGTs include hydrolyzable tannin-associated UGT84A73/JrGGT1 and UGT84A74/JrGGT2 (tahara2024elucidationandreconstitution pages 4-6) |
| Hydrolyzable tannin connection | Possible but unproven: walnut has characterized UGT84A family members involved in forming Ξ²-glucogallin from gallic acid + UDP-glucose, a key hydrolyzable tannin intermediate; whether LOC109005703 belongs to this exact functional clade is not established | Ξ²-Glucogallin formation is a key HT biosynthetic step catalyzed by gallic acid UGTs; walnut proteins JrGGT1/2 (UGT84A73/74) are cited as such enzymes (tahara2024elucidationandreconstitution pages 4-6) |
| Subcellular localization | Predicted localization: likely cytosol and/or endoplasmic reticulum-associated, as is common for many soluble plant UGTs involved in specialized metabolism; products may subsequently be trafficked to the vacuole | Related poplar UGT72 proteins localize to nucleus/ER or chloroplast-associated compartments depending on subgroup, illustrating family diversity; many glycosylated products are stored in vacuoles (speeckaert2020characterizationofthe pages 1-4, speeckaert2020characterizationofthe pages 6-10) |
| Confidence / evidence type | Evidence level for LOC109005703: low-to-moderate, based on domain architecture, family assignment, and homology-based inference; no direct experimental functional or localization data were identified for this specific walnut gene | No direct literature for LOC109005703 was retrieved; annotation rests on conserved UGT features and characterized homologs from walnut and other plants (gharabli2024thesugardonor pages 1-3, speeckaert2022ugt72amajor pages 2-5, tahara2024elucidationandreconstitution pages 4-6, speeckaert2020characterizationofthe pages 1-4) |
Table: This table summarizes the current evidence-based functional annotation for the walnut gene LOC109005703 (A0A2I4G8T1). It distinguishes direct identity information from homology-based inferences about catalytic mechanism, substrate scope, pathway context, and localization.
LOC109005703 from Juglans regia encodes a member of the UDP-glycosyltransferase superfamily predicted to catalyze the glycosylation of phenolic secondary metabolites. The protein possesses the conserved structural features characteristic of plant UGTs, including the PSPG motif-containing C-terminal domain for UDP-sugar binding and a variable N-terminal domain for acceptor recognition. Based on characterized walnut UGTs and related family members, LOC109005703 most likely functions in the phenylpropanoid pathway, potentially contributing to flavonoid glycosylation, hydrolyzable tannin biosynthesis, or monolignol homeostasis. The enzyme is predicted to localize to the cytoplasm and/or endoplasmic reticulum, consistent with other UGTs involved in specialized metabolism.
While this functional annotation provides a comprehensive framework based on the best available evidence, experimental validation through heterologous expression, enzyme assays with candidate substrates, and expression analysis in different walnut tissues and developmental stages would be required to definitively determine the biological role of LOC109005703 in walnut metabolism.
All evidence and citations are derived from the following sources cited in the text:
- pqac-00000000: Tahara et al. (2024) - Hydrolyzable tannin biosynthesis review
- pqac-00000001: Tahara et al. (2024) - Gallic acid formation and Ξ²-glucogallin synthesis
- pqac-00000002: Ren et al. (2022) - UGT gene family in Chinese bayberry, substrate specificity
- pqac-00000003: Ren et al. (2022) - Flavonoid glucosyltransferases
- pqac-00000004: Gharabli & Welner (2024) - Sugar donor specificity and catalytic mechanism
- pqac-00000005: Gharabli & Welner (2024) - PSPG motif structure and function
- pqac-00000006: Speeckaert et al. (2022) - UGT72 family review, phenylpropanoid pathway
- pqac-00000007: Speeckaert et al. (2022) - UGT evolutionary expansion and functions
- pqac-00000008: Tahara et al. (2024) - Walnut gallic acid UGTs and UGT84A family
- pqac-00000009: Speeckaert et al. (2020) - Poplar UGT72 characterization and localization
- pqac-00000010: Speeckaert et al. (2020) - UGT tissue expression and subcellular localization
References
(tahara2024elucidationandreconstitution pages 2-4): Ko Tahara, Carsten Milkowski, and Chihiro Oda-Yamamizo. Elucidation and reconstitution of hydrolyzable tannin biosynthesis. Plant Biotechnology, 41:203-212, Sep 2024. URL: https://doi.org/10.5511/plantbiotechnology.24.0601a, doi:10.5511/plantbiotechnology.24.0601a. This article has 11 citations and is from a peer-reviewed journal.
(speeckaert2022ugt72amajor pages 1-2): NathanaΓ«l Speeckaert, Mondher El Jaziri, Marie Baucher, and Marc Behr. Ugt72, a major glycosyltransferase family for flavonoid and monolignol homeostasis in plants. Biology, 11:441, Mar 2022. URL: https://doi.org/10.3390/biology11030441, doi:10.3390/biology11030441. This article has 44 citations.
(speeckaert2022ugt72amajor pages 2-5): NathanaΓ«l Speeckaert, Mondher El Jaziri, Marie Baucher, and Marc Behr. Ugt72, a major glycosyltransferase family for flavonoid and monolignol homeostasis in plants. Biology, 11:441, Mar 2022. URL: https://doi.org/10.3390/biology11030441, doi:10.3390/biology11030441. This article has 44 citations.
(gharabli2024thesugardonor pages 1-3): Hani Gharabli and Ditte Hededam Welner. The sugar donor specificity of plant family 1 glycosyltransferases. Frontiers in Bioengineering and Biotechnology, May 2024. URL: https://doi.org/10.3389/fbioe.2024.1396268, doi:10.3389/fbioe.2024.1396268. This article has 22 citations.
(speeckaert2020characterizationofthe pages 1-4): Nathanael Speeckaert, Nassirou Mahamadou Adamou, Hadjara Amadou Hassane, Fabien Baldacci-Cresp, Adeline Mol, Geert Goeminne, Wout Boerjan, Pierre Duez, Simon Hawkins, Godfrey Neutelings, Thomas Hoffmann, Wilfried Schwab, Mondher El Jaziri, Marc Behr, and Marie Baucher. Characterization of the udp-glycosyltransferase ugt72 family in poplar and identification of genes involved in the glycosylation of monolignols. International Journal of Molecular Sciences, 21:5018, Jul 2020. URL: https://doi.org/10.3390/ijms21145018, doi:10.3390/ijms21145018. This article has 52 citations.
(gharabli2024thesugardonor pages 3-4): Hani Gharabli and Ditte Hededam Welner. The sugar donor specificity of plant family 1 glycosyltransferases. Frontiers in Bioengineering and Biotechnology, May 2024. URL: https://doi.org/10.3389/fbioe.2024.1396268, doi:10.3389/fbioe.2024.1396268. This article has 22 citations.
(ren2022genomewideanalysisof pages 2-4): Chuanhong Ren, Yunlin Cao, Mengyun Xing, Yan Guo, Jiajia Li, Lei Xue, Chongde Sun, Changjie Xu, Kunsong Chen, and Xian Li. Genome-wide analysis of udp-glycosyltransferase gene family and identification of members involved in flavonoid glucosylation in chinese bayberry (morella rubra). Frontiers in Plant Science, Sep 2022. URL: https://doi.org/10.3389/fpls.2022.998985, doi:10.3389/fpls.2022.998985. This article has 38 citations.
(ren2022genomewideanalysisof pages 1-2): Chuanhong Ren, Yunlin Cao, Mengyun Xing, Yan Guo, Jiajia Li, Lei Xue, Chongde Sun, Changjie Xu, Kunsong Chen, and Xian Li. Genome-wide analysis of udp-glycosyltransferase gene family and identification of members involved in flavonoid glucosylation in chinese bayberry (morella rubra). Frontiers in Plant Science, Sep 2022. URL: https://doi.org/10.3389/fpls.2022.998985, doi:10.3389/fpls.2022.998985. This article has 38 citations.
(tahara2024elucidationandreconstitution pages 1-2): Ko Tahara, Carsten Milkowski, and Chihiro Oda-Yamamizo. Elucidation and reconstitution of hydrolyzable tannin biosynthesis. Plant Biotechnology, 41:203-212, Sep 2024. URL: https://doi.org/10.5511/plantbiotechnology.24.0601a, doi:10.5511/plantbiotechnology.24.0601a. This article has 11 citations and is from a peer-reviewed journal.
(tahara2024elucidationandreconstitution pages 4-6): Ko Tahara, Carsten Milkowski, and Chihiro Oda-Yamamizo. Elucidation and reconstitution of hydrolyzable tannin biosynthesis. Plant Biotechnology, 41:203-212, Sep 2024. URL: https://doi.org/10.5511/plantbiotechnology.24.0601a, doi:10.5511/plantbiotechnology.24.0601a. This article has 11 citations and is from a peer-reviewed journal.
(speeckaert2020characterizationofthe pages 6-10): Nathanael Speeckaert, Nassirou Mahamadou Adamou, Hadjara Amadou Hassane, Fabien Baldacci-Cresp, Adeline Mol, Geert Goeminne, Wout Boerjan, Pierre Duez, Simon Hawkins, Godfrey Neutelings, Thomas Hoffmann, Wilfried Schwab, Mondher El Jaziri, Marc Behr, and Marie Baucher. Characterization of the udp-glycosyltransferase ugt72 family in poplar and identification of genes involved in the glycosylation of monolignols. International Journal of Molecular Sciences, 21:5018, Jul 2020. URL: https://doi.org/10.3390/ijms21145018, doi:10.3390/ijms21145018. This article has 52 citations.
id: A0A2I4G8T1
gene_symbol: A0A2I4G8T1
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:51240
label: Juglans regia
description: >-
A0A2I4G8T1 is a UDP-glycosyltransferase from Juglans regia (English walnut),
belonging to the UGT73C subfamily based on PANTHER classification (PTHR48047:SF229,
UDP-GLYCOSYLTRANSFERASE 73C3-RELATED). The 488-amino-acid protein contains a
GT1_Gtf-like catalytic domain and a C-terminal UDP-glycosyltransferase signature
motif (UDPGT/Pfam PF00201), along with an N-terminal glycosyltransferase domain
(Pfam PF26168). As a GT1 family glycosyltransferase, it catalyzes the transfer of
sugar moieties from UDP-sugar donors to small-molecule acceptors. In plants, UGT73C
family members are known to glycosylate diverse substrates including brassinosteroids,
cytokinins, flavonoids, and other phenolic compounds, thereby modulating hormone
homeostasis and secondary metabolism. The protein is encoded on chromosome 3 and its
function is inferred entirely from homology, with no direct experimental
characterization reported.
existing_annotations:
- term:
id: GO:0035251
label: UDP-glucosyltransferase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
This IBA annotation is derived from phylogenetic inference (PANTHER) based on
orthology to six Arabidopsis UDP-glucosyltransferases (AT1G73880/UGT73C3,
AT2G36750, AT2G36790, AT2G36800, AT3G53160, AT5G03490). The protein contains
all expected domains (GT1_Gtf-like catalytic domain, UDPGT Pfam domain,
UDP-glycosyltransferase signature) and is classified in PANTHER subfamily
SF229 (UDP-GLYCOSYLTRANSFERASE 73C3-RELATED). UDP-glucosyltransferase
activity (GO:0035251) is more specific than the parent term
UDP-glycosyltransferase activity, specifying glucose as the sugar donor.
This is well supported by the phylogenetic context.
action: ACCEPT
reason: >-
The phylogenetic placement with multiple Arabidopsis UGT73 family members,
combined with domain architecture (GT1_Gtf-like, UDPGT, UDP_glycos_trans_CS),
strongly supports UDP-glucosyltransferase activity. This is the most specific
and informative annotation among the three.
- term:
id: GO:0008194
label: UDP-glycosyltransferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
This IEA annotation comes from the InterPro domain IPR002213
(UDP-glucosyltransferase), which is present in the protein. The annotation
to GO:0008194 (UDP-glycosyltransferase activity) is correct but is a parent
term of the more specific GO:0035251 (UDP-glucosyltransferase activity)
already assigned by IBA. It is redundant given the more specific annotation.
action: KEEP_AS_NON_CORE
reason: >-
This is a true parent term of GO:0035251. The protein does have
UDP-glycosyltransferase activity, but the more specific
UDP-glucosyltransferase activity better captures its function. Keeping as
non-core since it is correct but less informative.
- term:
id: GO:0016757
label: glycosyltransferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: enables
review:
summary: >-
This IEA annotation from ARBA assigns the very broad parent term
glycosyltransferase activity (GO:0016757). While correct, this is overly
general given that more specific terms (GO:0035251, GO:0008194) are already
assigned. GO:0016757 encompasses all glycosyltransferases regardless of donor
substrate, while this protein clearly belongs to the UDP-dependent GT1 family.
action: MARK_AS_OVER_ANNOTATED
reason: >-
This is the broadest of the three molecular function annotations and adds no
information beyond what is captured by the more specific terms. The protein's
domain architecture and phylogenetic placement clearly place it in the
UDP-glycosyltransferase family, making this overly general annotation
uninformative.
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO
terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings:
- statement: >-
Phylogenetic inference places A0A2I4G8T1 with Arabidopsis UGT73 family
glucosyltransferases
supporting_text: >-
IBA based on orthology to AT1G73880 (UGT73C3), AT2G36750, AT2G36790,
AT2G36800, AT3G53160, AT5G03490
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
core_functions:
- description: >-
A0A2I4G8T1 functions as a UDP-glucosyltransferase, catalyzing the transfer
of glucose from UDP-glucose to small-molecule acceptor substrates. Based on
its classification in the UGT73C subfamily, likely substrates include
brassinosteroids, flavonoids, or other phenolic compounds, though the
specific in vivo acceptor in walnut has not been experimentally determined.
molecular_function:
id: GO:0035251
label: UDP-glucosyltransferase activity
supported_by:
- reference_id: GO_REF:0000033
supporting_text: >-
IBA annotation from phylogenetic trees, based on orthology to six
Arabidopsis UDP-glucosyltransferases
suggested_questions:
- question: >-
What are the in vivo acceptor substrates of this UGT73C-related
glucosyltransferase in Juglans regia? Walnut produces abundant
naphthoquinones (e.g. juglone) and phenolics that could be glycosylation
targets.
experts: []
- question: >-
Does this enzyme glycosylate juglone (5-hydroxy-1,4-naphthoquinone), the
characteristic allelochemical of walnut, potentially serving a detoxification
or storage role?
experts: []
suggested_experiments:
- description: >-
In vitro substrate screening of recombinant A0A2I4G8T1 with
UDP-glucose and candidate acceptors including juglone, quercetin,
kaempferol, brassinolide, and trans-zeatin to determine substrate specificity.
hypothesis: >-
Given its UGT73C subfamily classification and the prominence of juglone in
walnut metabolism, the enzyme may glycosylate juglone or related
naphthoquinones as a detoxification mechanism.
- description: >-
Expression profiling of LOC109005703 across walnut tissues (leaves, roots,
hull, bark) and developmental stages to identify where glycosylation activity
is most needed.
hypothesis: >-
Expression may be highest in tissues with active secondary metabolism or
juglone production, suggesting a role in phenolic compound homeostasis.