FATTY ACID ELONGATION1 (FAE1) of field pennycress is the seed-expressed 3-ketoacyl-CoA synthase (condensing enzyme) of the endoplasmic reticulum acyl-CoA elongase. It catalyzes the chain-length-determining condensation of malonyl-CoA with oleoyl-CoA and eicosenoyl-CoA, the first of four reactions in each elongation cycle, producing the eicosenoic (20:1) and erucic (22:1) very-long-chain fatty acids that make up roughly 35-40% of wild pennycress seed oil and are stored mainly in triacylglycerol. The gene is highly expressed early in seed development. Loss-of-function alleles abolish erucic acid and nearly abolish eicosenoic acid in seed oil, raising oleic and polyunsaturated fatty acids without obvious effects on vegetative growth; such alleles underlie low-erucic, canola-like pennycress oil and are combined with fad2 or rod1 mutations to produce high-oleic oil. FAE1 belongs to the plant 3-ketoacyl-CoA synthase (KCS) family and is orthologous to Arabidopsis FAE1/KCS18.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000117 | ACCEPT | Summary: ER localization predicted by ARBA from the plant KCS family. Reason: No localization data exist for pennycress FAE1, but the acyl-CoA elongase is an ER membrane complex and the Arabidopsis ortholog (KCS18) is an ER enzyme. The prediction is consistent with the enzyme's established biochemistry and with the 1-residue identity of this protein to the reference-proteome FAE1. Supporting Evidence: PMID:33968108 Fatty acid (FA) elongation of 18:1-CoA is carried out by a protein complex containing the FA elongase, FAE1. file:THLAR/FAE1/FAE1-deep-research-falcon.md The enzyme localizes to the endoplasmic reticulum membrane, where it operates as part of a multi-component complex including KCR, HCD, and ECR enzymes |
| GO:0006633 fatty acid biosynthetic process | IEA GO_REF:0000120 | MODIFY | Summary: Correct but too general; FAE1 elongates C18 acyl-CoAs to very-long-chain fatty acids. Reason: FAE1 performs the condensation step of very-long-chain fatty acid synthesis, not de novo (plastid) fatty acid synthesis. Knockout in pennycress specifically removes the C20:1 and C22:1 products, so the more precise process term is appropriate. Proposed replacements: very long-chain fatty acid biosynthetic process Supporting Evidence: PMID:30230695 The pennycress fae1‐3 mutant harbours a 4‐bp deletion in the TaFAE1 coding sequence, producing seed oil (triacylglycerols; TAG) with undetectable amounts of erucic acid (C22:1) and greatly reduced amounts of eicosenoic acid (C20:1). |
| GO:0009922 fatty acid elongase activity | IEA GO_REF:0000003 | ACCEPT | Summary: The core catalytic activity; the GO term is defined by the KCS condensation reaction. Reason: GO:0009922 is defined as the condensation of a very-long-chain acyl-CoA with malonyl-CoA, exactly the FAE1 reaction. Heterologous expression of pennycress FAE1 raises erucic acid in Arabidopsis seed, and CRISPR knockout in pennycress abolishes elongation products. Supporting Evidence: PMID:32740897 Seed-specific expression of the Pennycress FAE1 gene in Col-0 resulted in a 3 to fourfold increase of erucic acid content in the seed oil. PMID:30230695 CRISPR‐Cas9‐induced mutations in the putative TaFAE1 gene abolish erucic acid content in pennycress seed triacylglycerols |
| GO:0016020 membrane | IEA GO_REF:0000120 | MODIFY | Summary: Correct but uninformative; the membrane is the ER membrane. Reason: KCS condensing enzymes are N-terminally anchored ER membrane proteins; the specific compartment is the ER membrane, consistent with the ARBA ER prediction above. Proposed replacements: endoplasmic reticulum membrane |
| GO:0016746 acyltransferase activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Generic thiolase-like-fold mapping; true but subsumed by fatty acid elongase activity. Reason: Fatty acid elongase activity is a descendant of acyltransferase activity, so this term is correct but adds no information beyond the specific MF annotation. |
| GO:0016747 acyltransferase activity, transferring groups other than amino-acyl groups | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: True parent of the specific KCS activity; uninformative. Reason: Correct ancestor of fatty acid elongase activity; retained as non-core because the specific term is present. |
| GO:0042761 very long-chain fatty acid biosynthetic process | IMP PMID:30230695 Molecular tools enabling pennycress (Thlaspi arvense) as a m... | NEW | Summary: FAE1 catalyzes the committed condensation step of seed VLCFA synthesis in pennycress. Reason: FAE1 itself performs a step of this process (the condensation reaction), so this is participation, not mere requirement. CRISPR knockouts in pennycress remove erucic acid and nearly all eicosenoic acid from seed oil, confirming that this gene is the seed elongase. The same term is also the proposed replacement for the GO:0006633 IEA row above; this NEW row is deliberate and separate, adding pennycress-specific mutant (IMP) evidence. Supporting Evidence: PMID:30230695 Seeds from homozygous fae1‐3, fae1‐4 and fae1‐5 plants were analysed for TAG fatty acid composition, revealing negligible amounts of erucic (C22:1) and eicosenoic (C20:1) acids in all three lines PMID:39657724 FATTY ACID ELONGATION1 (FAE1) was targeted using CRISPR-Cas 9 gene editing to eliminate very long chain fatty acids (VLCFAs) from pennycress seed oil |
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Download this section (compressed HTML)Q: Does pennycress FAE1 form the same ER elongase complex (KCR1, PAS2/HCD, ECR/CER10) as in Arabidopsis, and are the downstream elongase components seed-limiting for erucic acid?
Q: Which of the fixed FAE1 residues distinguishing high- and low-erucic Brassicaceae explain pennycress FAE1's reported preference for eicosenoyl-CoA over oleoyl-CoA?
Experiment: In vitro or yeast assay of recombinant pennycress FAE1 with C18:1-, C20:1- and C22:1-CoA to measure substrate preference directly rather than inferring it from seed oil.
Experiment: Fluorescent-protein fusion of TaFAE1 in pennycress or N. benthamiana to confirm ER membrane localization.
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