At1g67980 encodes a putative caffeoyl-CoA O-methyltransferase (CCoAOMT-6), a Class II member of the 7-gene Arabidopsis CCoAOMT family. The protein has the canonical cation-dependent, SAM-dependent O-methyltransferase fold (IPR050362, IPR002935) but has NOT been directly biochemically characterized. Its function is inferred entirely by similarity to characterized CCoAOMT enzymes from alfalfa and other species. At1g67980 is a tandem duplicate of At1g67990 (AtTSM1), which is tapetum-specific and methylates spermidine-hydroxycinnamic acid conjugates rather than lignin precursors. The principal lignin-pathway CCoAOMT in Arabidopsis is CCoAOMT1 (At4g34050, Class I). Class II members including At1g67980 may have broader substrate specificity toward flavonoids and other phenolics, with functions potentially divergent from lignin biosynthesis. In the absence of direct experimental evidence, the biological role of At1g67980 remains uncertain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008757 S-adenosylmethionine-dependent methyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: At1g67980 contains the Class I-like SAM-dependent O-methyltransferase domain (IPR002935) and the SAM-dependent methyltransferase superfamily fold (IPR029063). The IBA annotation via PANTHER phylogenetic inference is well-supported by sequence conservation of SAM-binding residues documented across the CCoAOMT family. Supporting Evidence: PMID:9484457 Five highly conserved regions are proposed as a signature for plant O-methyltransferases, two of which (regions I and IV) are believed to be involved in S-adenosyl-L-methionine and metal binding, respectively. |
| GO:0008171 O-methyltransferase activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: The O-methyltransferase activity annotation is inferred from the IPR002935 (Class I-like SAM-dependent O-methyltransferase) domain. This is a broad functional term that is consistent with the domain architecture and family membership. However, it is less specific than the caffeoyl-CoA O-methyltransferase annotation (GO:0042409) and is redundant with it. Reason: This is a parent term of caffeoyl-CoA O-methyltransferase activity and is redundant if the more specific term is retained. Keep as non-core since it is technically correct but adds no information beyond GO:0042409. |
| GO:0042409 caffeoyl-CoA O-methyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Assigned based on EC 2.1.1.104 via Rhea reaction mapping. At1g67980 has the canonical CCoAOMT domain architecture and is classified in the CCoAOMT subfamily by UniProt. However, no direct biochemical assay has been performed on the At1g67980 gene product itself. The neighboring tandem duplicate At1g67990 (AtTSM1) has been shown to prefer caffeic acid esters and spermidine conjugates over caffeoyl-CoA, and Ibdah et al. (2003) showed that Arabidopsis Class II CCoAOMTs can have broader substrate specificity including flavonols and caffeoylglucose. The annotation is plausible but should be considered provisional. Reason: The EC number assignment and domain architecture support this annotation, and the IEA evidence appropriately reflects the uncertainty. Accepting as the most specific MF term available, but note the protein is genuinely putative. Supporting Evidence: PMID:12941960 the enzymes from the Centrospermae, along with the predicted gene product from A. thaliana, form a novel subclass within the caffeoyl coenzyme A-dependent O-methyltransferases, with potential divergent functions not restricted to lignin monomer biosynthesis file:ARATH/At1g67980/At1g67980-deep-research-bioreason-sft.md BioReason domain analysis correctly identifies the SAM-dependent methyltransferase fold and cation-dependent O-methyltransferase family, supporting the CCoAOMT activity annotation file:ARATH/At1g67980/At1g67980-deep-research-falcon.md within the retrieved corpus, there is **no direct biochemical characterization** (purified enzyme assay, kinetic parameters, definitive substrate specificity, metal dependence) and **no direct subcellular localization experiment** specifically for **AT1G67980/Q9C9W3**. file:ARATH/At1g67980/At1g67980-deep-research-falcon.md CCoAOMT-family enzymes catalyze **O-methylation reactions** in **monolignol synthesis** affecting lignification and lignin composition; CCoAOMT-like enzymes can be more **substrate-promiscuous**, acting on compounds such as flavonoids, anthocyanins, phenylpropanoids, or alkaloids |
| GO:0009699 phenylpropanoid biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: Inferred from UniPathway mapping (UPA00711). CCoAOMT enzymes operate within the phenylpropanoid pathway broadly, catalyzing methylation of hydroxycinnamic acid CoA esters. This is a reasonable general biological process annotation for any CCoAOMT family member, since even Class II members with broader substrate specificity act on phenylpropanoid-derived substrates. Reason: Phenylpropanoid biosynthesis is appropriate as a broad process annotation. Even if At1g67980 does not specifically function in lignin biosynthesis, it would still participate in phenylpropanoid metabolism given its domain architecture and family membership. Supporting Evidence: file:ARATH/At1g67980/At1g67980-deep-research-falcon.md A 2024 Arabidopsis lignification-focused thesis compilation explicitly includes **AT1G67980 as CCoAOMT6** in the **phenylpropanoid/monolignol biosynthesis** section, supporting continued use of this locus in modern lignification pathway models file:ARATH/At1g67980/At1g67980-deep-research-falcon.md In Arabidopsis roots treated with cellooligomers, **AT1G67980 (CCOAOMT)** was upregulated **3.67-fold** with **p = 6.47 × 10−5**; the study interprets the induced program as involving **cell wall reinforcement** and **defense-related secondary metabolite synthesis** requiring the receptor kinase CORK1 |
| GO:0005737 cytoplasm | ISM GO_REF:0000122 | KEEP AS NON CORE | Summary: Predicted by AtSubP subcellular localization analysis. CCoAOMT enzymes are generally soluble cytoplasmic proteins. The protein lacks signal peptides or transmembrane domains. The neighboring At1g67990 (AtTSM1) was confirmed cytoplasmic. This annotation is consistent but cytosol (GO:0005829) is more specific. Reason: The cytoplasm annotation is technically correct but less specific than the cytosol annotation (GO:0005829) already present. Redundant with cytosol. |
| GO:0009507 chloroplast | ISM GO_REF:0000122 | REMOVE | Summary: Predicted by AtSubP subcellular localization analysis. However, CCoAOMT enzymes are characteristically cytosolic. The protein lacks a chloroplast transit peptide. The related At1g67990 protein was demonstrated to be cytoplasmic. CCoAOMT1 (At4g34050) is also cytosolic. No published evidence supports chloroplast localization for any CCoAOMT family member. This is likely a false positive from the prediction algorithm. Reason: No evidence supports chloroplast localization for any CCoAOMT. The protein lacks a transit peptide, and characterized family members are cytosolic. This is likely a computational false positive. Supporting Evidence: file:ARATH/At1g67980/At1g67980-deep-research-falcon.md No retrieved source in this run provides direct experimental evidence (e.g., GFP fusion, fractionation) for AT1G67980 subcellular localization (kuo2024dissectingtheroles pages 30-32, tseng2022cork1alrrmalectin pages 17-18). Any cellular-location statement would be speculative; consequently, localization remains **undetermined from the current evidence set**. |
| GO:0005829 cytosol | TAS PMID:9484457 Plant O-methyltransferases: molecular analysis, common signa... | ACCEPT | Summary: The TAS annotation references Ibrahim et al. (1998), a review of plant O-methyltransferases that classifies them and discusses their conserved features. CCoAOMT-type enzymes are soluble, cation-dependent methyltransferases that function in the cytosol. The fern PaCCoAOMT-GFP fusion was shown to localize to cytoplasm. The neighboring At1g67990 (AtTSM1) is also cytoplasmic. The TAS evidence is appropriate given the broad family characterization. Supporting Evidence: PMID:9484457 Comparative analysis of the predicted amino acid sequences of a number of plant O-methyltransferase cDNA clones show that they share some 32-71% sequence identity PMID:30685696 The transient expression of a PaCCoAOMT-GFP fusion gene in tobacco demonstrated that in planta, PaCCoAOMTs are likely directed to the cytoplasm. |
| GO:0009809 lignin biosynthetic process | ISS PMID:9662519 Developmental expression and substrate specificities of alfa... | MARK AS OVER ANNOTATED | Summary: The ISS annotation is based on sequence similarity to alfalfa CCoAOMT, which is directly involved in lignin monolignol biosynthesis. However, this annotation is problematic for At1g67980 specifically. The principal lignin-pathway CCoAOMT in Arabidopsis is CCoAOMT1 (At4g34050, Class I). At1g67980 is a Class II member, and its tandem duplicate At1g67990 functions in tapetum-specific spermidine conjugate biosynthesis rather than lignin. Ibdah et al. (2003) showed Class II members may have divergent functions beyond lignin. Without direct evidence that At1g67980 contributes to lignin biosynthesis, this annotation may represent over-annotation by similarity. Reason: The ISS evidence is from alfalfa CCoAOMT (Class I equivalent). At1g67980 is a Class II CCoAOMT whose closest paralog (At1g67990) has a non-lignin function. The actual lignin CCoAOMT in Arabidopsis is At4g34050. Annotating At1g67980 to lignin biosynthesis based on similarity to a different class of CCoAOMT is likely over-annotation. Supporting Evidence: PMID:18557837 In Arabidopsis thaliana individual members of this gene family are temporally and spatially regulated...The gene At1g67990 is specifically expressed in flower buds PMID:12941960 the enzymes from the Centrospermae, along with the predicted gene product from A. thaliana, form a novel subclass...with potential divergent functions not restricted to lignin monomer biosynthesis file:ARATH/At1g67980/At1g67980-deep-research-falcon.md A 2024 Arabidopsis lignification-focused thesis compilation explicitly includes **AT1G67980 as CCoAOMT6** in the **phenylpropanoid/monolignol biosynthesis** section, supporting continued use of this locus in modern lignification pathway models file:ARATH/At1g67980/At1g67980-deep-research-falcon.md within the retrieved corpus, there is **no direct biochemical characterization** (purified enzyme assay, kinetic parameters, definitive substrate specificity, metal dependence) and **no direct subcellular localization experiment** specifically for **AT1G67980/Q9C9W3**. |
Loading supporting content…
Download this section (compressed HTML)Q: What is the true substrate specificity of the At1g67980 protein? Does it preferentially methylate caffeoyl-CoA (like Class I CCoAOMTs), or does it have broader specificity toward flavonoids and other phenolics (as suggested for Class II members)?
Suggested experts: Thomas Vogt
Q: What is the expression pattern of At1g67980? Is it co-expressed with lignin biosynthetic genes (suggesting a role in lignin) or with flavonoid/pollen coat genes (suggesting a function more similar to its tandem duplicate At1g67990/AtTSM1)?
Suggested experts: Christin Fellenberg, Thomas Vogt
Q: Does At1g67980 have redundant function with CCoAOMT1 (At4g34050) in lignin biosynthesis, or does it serve a distinct biological role?
Suggested experts: Richard A Dixon
Experiment: Express recombinant At1g67980 protein in E. coli and test enzymatic activity against a panel of substrates including caffeoyl-CoA, 5-hydroxyferuloyl-CoA, caffeic acid, caffeoylglucose, and common flavonoids (quercetin, luteolin). Compare kinetic parameters (Km, kcat) with those of CCoAOMT1 (At4g34050) and AtTSM1 (At1g67990).
Hypothesis: At1g67980 has caffeoyl-CoA O-methyltransferase activity with potentially broader substrate specificity than CCoAOMT1.
Type: biochemical assay
Experiment: Generate promoter-GUS reporter lines for At1g67980 and examine expression across developmental stages and tissues. Compare with published expression data for CCoAOMT1 (vascular tissue, roots) and AtTSM1 (tapetum-specific). Alternatively, analyze publicly available RNA-seq data from TAIR/Araport for tissue-specific expression.
Hypothesis: At1g67980 has a tissue-specific expression pattern distinct from CCoAOMT1.
Type: gene expression analysis
Experiment: Obtain T-DNA insertion mutants for At1g67980 and analyze cell wall composition (lignin content and monomer composition by thioacidolysis), scopoletin/scopolin levels in roots, and phenolic profiles in various tissues. Compare with ccoaomt1 mutant phenotypes. Generate double mutants if single mutants show no phenotype.
Hypothesis: At1g67980 contributes to lignin biosynthesis or other phenylpropanoid pathways.
Type: reverse genetics and metabolite profiling
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)