SYP121 (also PEN1, SYR1) is a plasma-membrane Qa-SNARE (syntaxin) of Arabidopsis thaliana, a C-terminally tail-anchored protein with an N-terminal Habc regulatory domain and a SNARE motif. It contributes the Qa helix to ternary SNARE complexes with the Qbc-SNARE SNAP33 and the vesicular R-SNAREs VAMP721/VAMP722, driving fusion of secretory vesicles with the plasma membrane; assembly is regulated by the SM protein SEC11/KEULE and coordinated with the exocyst (EXO70A1). Partly redundantly with its paralog SYP122, it supports constitutive secretion for growth and delivers membrane cargo such as PIP aquaporins (with SYP61) and KAT1 K+ channels. Upon attack by powdery mildew fungi it is recruited beneath appressoria and mediates the focal secretion that builds papillae and confers pre-invasive (penetration) resistance to non-adapted fungi such as Blumeria graminis f. sp. hordei. Independently of fusion, its N-terminal FxRF motif binds the K+ channel subunit KC1 (and KAT1), promoting AKT1/KC1 channel gating for K+ uptake and contributing to guard-cell K+ channel recycling and stomatal reopening.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000149 SNARE binding | IBA GO_REF:0000033 | ACCEPT | Summary: SYP121 is a Qa-SNARE that binds its cognate Qbc-SNARE SNAP33 and R-SNAREs VAMP721/722 to form ternary SNARE complexes; it also binds the SM protein SEC11. SNARE binding is the conserved syntaxin-family activity placed by PAINT at the family node. Reason: The IBA is phylogenetically sound and is directly confirmed for SYP121 by in vitro and in planta SNARE complex formation with SNAP33 and VAMP721/722. Supporting Evidence: PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) PMID:18678865 Our findings are consistent with the hypothesis that PEN1 acts in plant defense through the formation of ternary SNARE complexes |
| GO:0005484 helical-bundle zippering fusogenic activity | IBA GO_REF:0000033 | ACCEPT | Summary: SYP121 contributes the Qa (syntaxin) helix to the four-helix trans-SNARE bundle that drives fusion of secretory vesicles with the plasma membrane; GO:0005484 (formerly SNAP receptor activity) is the canonical MF for syntaxins. Reason: Core molecular function. Phylogenetically placed IBA, consistent with ternary SNARE complex formation by SYP121 with SNAP33 and VAMP721/722 and loss of defense activity in SNARE-domain variants that fail to form ternary complexes. Supporting Evidence: PMID:18678865 Our findings are consistent with the hypothesis that PEN1 acts in plant defense through the formation of ternary SNARE complexes PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0005484 helical-bundle zippering fusogenic activity | IEA GO_REF:0000120 | ACCEPT | Summary: SYP121 contributes the Qa (syntaxin) helix to the four-helix trans-SNARE bundle that drives fusion of secretory vesicles with the plasma membrane; GO:0005484 (formerly SNAP receptor activity) is the canonical MF for syntaxins. Reason: Consistent with the IBA and experimental data; syntaxin/SNARE domain mapping is reliable for this canonical Qa-SNARE. Supporting Evidence: PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0005484 helical-bundle zippering fusogenic activity | TAS PMID:11115874 The Arabidopsis genome. An abundance of soluble N-ethylmalei... | ACCEPT | Summary: SYP121 contributes the Qa (syntaxin) helix to the four-helix trans-SNARE bundle that drives fusion of secretory vesicles with the plasma membrane; GO:0005484 (formerly SNAP receptor activity) is the canonical MF for syntaxins. Reason: The genome survey of Arabidopsis SNAREs classifies SYP121 as a plasma-membrane syntaxin contributing a helix to the SNARE bundle; correct, though superseded in strength by experimental evidence. Supporting Evidence: PMID:11115874 One of the helices is always derived from a member of the syntaxin family of SNAREs, whereas the other two helices come from other types of SNAREs |
| GO:0005515 protein binding | IPI PMID:18273019 Co-option of a default secretory pathway for plant immune re... | MODIFY | Summary: IPI with SNAP33 (Q9S7P9) from Kwon et al. 2008: PEN1 forms SDS-resistant SNARE complexes with the Qbc-SNARE SNAP33 and VAMP721/722. Reason: Protein binding is uninformative; the partner is a cognate SNARE, so SNARE binding (GO:0000149) captures the interaction. Proposed replacements: SNARE binding Supporting Evidence: PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0005515 protein binding | IPI PMID:21115662 A molecular framework for coupling cellular volume and osmot... | MODIFY | Summary: IPI with the K+ channel KAT1 (AT5G46240) from Honsbein et al. 2011, which reports selective interaction of SYP121 with Kv-like K+ channels. Reason: Protein binding is uninformative. SYP121 binds K+ channel subunits (KC1, KAT1) via its N-terminal FxRF motif and alters their gating; transmembrane transporter binding (GO:0044325) is the informative binding term, and the functional consequence is captured as a NEW potassium channel regulator activity annotation. Proposed replacements: transmembrane transporter binding Supporting Evidence: PMID:21115662 new evidence is provided of a wider participation among Arabidopsis Kv-like K(+) channels in selective interaction with the vesicle-trafficking protein SYP121 PMID:30850468 However, SYP121 also interacts with the K+ channels KC1 and KAT1, altering channel gating to promote K+ uptake |
| GO:0005515 protein binding | IPI PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | MODIFY | Summary: IPI with aquaporin PIP2;7 (P93004) from Hachez et al. 2014 (co-IP/BiFC). Reason: Protein binding is uninformative. PIP2;7 is a cargo water channel; transmembrane transporter binding (GO:0044325) is the more informative term. The interaction is non-core relative to SNARE fusogenic activity. Proposed replacements: transmembrane transporter binding Supporting Evidence: PMID:25082856 post-Golgi trafficking of PIP2;7 in Arabidopsis thaliana involves specific interactions with two syntaxin proteins, namely, the Qc-SNARE SYP61 and the Qa-SNARE SYP121 |
| GO:0005515 protein binding | IPI PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | MODIFY | Summary: IPI with SYP61 (Q946Y7) from Hachez et al. 2014: SYP61 and SYP121 co-immunoprecipitate and are proposed to form a SNARE complex. Reason: Protein binding is uninformative; partner is a Qc-SNARE, so SNARE binding (GO:0000149) is appropriate. Proposed replacements: SNARE binding Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0005515 protein binding | IPI PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | MODIFY | Summary: IPI with SYP61 (AT1G28490) from Hachez et al. 2014 (duplicate row with locus-code identifier). Reason: As for the UniProt-identified SYP61 row: replace protein binding with SNARE binding. Proposed replacements: SNARE binding Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0005515 protein binding | IPI PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | MODIFY | Summary: IPI with PIP2;7 (AT4G35100) from Hachez et al. 2014 (duplicate row with locus-code identifier). Reason: As for the UniProt-identified PIP2;7 row: replace protein binding with transmembrane transporter binding. Proposed replacements: transmembrane transporter binding Supporting Evidence: PMID:25082856 post-Golgi trafficking of PIP2;7 in Arabidopsis thaliana involves specific interactions with two syntaxin proteins, namely, the Qc-SNARE SYP61 and the Qa-SNARE SYP121 |
| GO:0005515 protein binding | IPI PMID:30850468 Dual Sites for SEC11 on the SNARE SYP121 Implicate a Binding... | REMOVE | Summary: IPI with the SM protein SEC11/KEULE (AT1G12360) from Karnik et al. 2015/Waghmare-Blatt group: SEC11 binds SYP121 at two sites, regulating SNARE assembly. Reason: Protein binding is uninformative, but there is no specific GO MF for binding an SM protein from the syntaxin side (syntaxin binding describes SEC11, not SYP121). The interaction is genuine and regulatory, but a bare protein-binding row carries no functional information, so it is removed; removal does not mean the interaction is false. Supporting Evidence: PMID:30850468 Notably, SEC11 binds preferentially with SYP121 and rescues traffic block by dominant-negative fragments of the SNAREs when these fragments are expressed, but only in plants that also express the native SYP121 |
| GO:0005515 protein binding | IPI PMID:32699172 Synergy among Exocyst and SNARE Interactions Identifies a Fu... | MODIFY | Summary: IPI with VAMP721 (AT1G04750) from Larson et al. 2020 (split-ubiquitin/FRET); VAMP721 is the cognate R-SNARE of SYP121. Reason: Protein binding is uninformative; partner is an R-SNARE, so SNARE binding (GO:0000149). Proposed replacements: SNARE binding Supporting Evidence: PMID:32699172 exocyst EXO70 subunits bind preferentially to cognate plasma membrane SNAREs, notably SYP121 and VAMP721 |
| GO:0005515 protein binding | IPI PMID:32699172 Synergy among Exocyst and SNARE Interactions Identifies a Fu... | REMOVE | Summary: IPI with the exocyst subunit EXO70A1 (AT5G03540) from Larson et al. 2020. Reason: Protein binding is uninformative but no exocyst-binding MF term exists in GO; the tethering-complex interaction is genuine and functionally supported by genetics, but a bare protein-binding row carries no functional information, so it is removed; removal does not mean the interaction is false. Supporting Evidence: PMID:32699172 exocyst EXO70 subunits bind preferentially to cognate plasma membrane SNAREs, notably SYP121 and VAMP721 |
| GO:0005794 Golgi apparatus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Golgi apparatus by UniProt subcellular-location mapping (from trans-Golgi network membrane). Reason: SYP121 is principally plasma-membrane resident but transits/recycles through TGN/early endosome compartments; the Golgi term derives from TGN localization and is not where SYP121 acts. Supporting Evidence: PMID:25082856 Among the plasma membrane-resident syntaxins, SYNTAXIN OF PLANTS121 (SYP121) is known to mediate the trafficking of vesicles between the Golgi complex and the plasma membrane PMID:21707889 syntaxin in innate immunity does not need upregulation of expression but instead requires pathogen-induced and endocytosis-dependent retargeting to the infection site. |
| GO:0005802 trans-Golgi network | IDA PMID:21707889 Mechanisms of functional specificity among plasma-membrane s... | KEEP AS NON CORE | Summary: TGN localization from Reichardt et al. 2011, consistent with endocytosis-dependent recycling of PEN1 through TGN/early endosomes. Reason: Supported but represents a trafficking/recycling pool rather than the site of SYP121 fusogenic activity (the plasma membrane). Supporting Evidence: PMID:21707889 syntaxin in innate immunity does not need upregulation of expression but instead requires pathogen-induced and endocytosis-dependent retargeting to the infection site. |
| GO:0005829 cytosol | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | MARK AS OVER ANNOTATED | Summary: Cytosol from a high-throughput protein correlation profiling study. Reason: SYP121 is a C-terminally tail-anchored integral membrane protein; its N-terminal domain faces the cytosol, but the protein is not a soluble cytosolic protein. The HDA detection in a cytosolic fraction most likely reflects fractionation behaviour. Supporting Evidence: PMID:28887381 Profiling of a sucrose velocity gradient of microsomal membranes was used to determine which of proteins identified in both the cholate-soluble fraction and cytosol fraction were βtrueβ membrane-associated versus cytosolic contaminants based on penetration depth into the sucrose gradient. file:ARATH/SYP121/SYP121-deep-research-falcon.md SYP121 is principally **resident at the plasma membrane** |
| GO:0005886 plasma membrane | EXP PMID:15342965 Systematic analysis of SNARE molecules in Arabidopsis: disse... | ACCEPT | Summary: Plasma membrane localization of GFP-SYP121 in the systematic SNARE localization survey of Uemura et al. 2004. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:15342965 17 on the plasma membrane |
| GO:0005886 plasma membrane | EXP PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | ACCEPT | Summary: Plasma membrane localization from Hachez et al. 2014. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:25082856 Among the plasma membrane-resident syntaxins, SYNTAXIN OF PLANTS121 (SYP121) is known to mediate the trafficking of vesicles between the Golgi complex and the plasma membrane |
| GO:0005886 plasma membrane | HDA PMID:15060130 Identification of new intrinsic proteins in Arabidopsis plas... | ACCEPT | Summary: Detected in a purified plasma membrane proteome. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:15060130 We produced from Arabidopsis cell suspensions a highly purified plasma membrane fraction and characterized it in detail by immunological and enzymatic tests. |
| GO:0005886 plasma membrane | HDA PMID:17644812 A high content in lipid-modified peripheral proteins and int... | ACCEPT | Summary: Detected in a purified plasma membrane proteome. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:17644812 A highly purified plasma membrane fraction was washed by NaCl and Na2CO3 salts, and the insoluble fractions were further analyzed by nano-LC-MS/MS. |
| GO:0005886 plasma membrane | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | ACCEPT | Summary: Assigned to plasma membrane by LOPIT organelle proteomics. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:22923678 as well as the localization of 304 endoplasmic reticulum and 208 plasma membrane proteins |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA: plasma-membrane syntaxins are active at the plasma membrane. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: file:ARATH/SYP121/SYP121-deep-research-falcon.md SYP121 is principally **resident at the plasma membrane** PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0005886 plasma membrane | IDA PMID:14586469 SNARE-protein-mediated disease resistance at the plant cell ... | ACCEPT | Summary: Plasma membrane location of PEN1 from Collins et al. 2003. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:14586469 Genetic control of vesicle behaviour at penetration sites, and plasma membrane location of PEN1/ROR2, is consistent with a proposed involvement of SNARE-complex-mediated exocytosis and/or homotypic vesicle fusion events in resistance. |
| GO:0005886 plasma membrane | IDA PMID:16935987 Overexpression of the Arabidopsis syntaxin PEP12/SYP21 inhib... | ACCEPT | Summary: YFP-SYP121 used as plasma membrane marker in the SYP21 overexpression study. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:16935987 the syntaxin YFP-SYP121 strongly labels the plasma membrane when expressed in protoplasts, giving a characteristic ring pattern |
| GO:0005886 plasma membrane | IDA PMID:21707889 Mechanisms of functional specificity among plasma-membrane s... | ACCEPT | Summary: Plasma membrane localization from Reichardt et al. 2011. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:21707889 The Arabidopsis SYP1 family of plasma membrane-localized syntaxins comprises nine members, of which KNOLLE and PEN1 play specific roles in cytokinesis and innate immunity, respectively. |
| GO:0005886 plasma membrane | IDA PMID:32699172 Synergy among Exocyst and SNARE Interactions Identifies a Fu... | ACCEPT | Summary: Plasma membrane localization from Larson et al. 2020. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:32699172 exocyst EXO70 subunits bind preferentially to cognate plasma membrane SNAREs, notably SYP121 and VAMP721 |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Plasma membrane by UniProt subcellular-location mapping. Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:25082856 Among the plasma membrane-resident syntaxins, SYNTAXIN OF PLANTS121 (SYP121) is known to mediate the trafficking of vesicles between the Golgi complex and the plasma membrane |
| GO:0005886 plasma membrane | TAS PMID:11115874 The Arabidopsis genome. An abundance of soluble N-ethylmalei... | ACCEPT | Summary: Plasma membrane from the Arabidopsis SNARE genome survey (Sanderfoot et al. 2000). Reason: Plasma membrane is the principal residence and site of action of SYP121, established by fluorescent fusions, fractionation and proteomics. Supporting Evidence: PMID:11115874 AtSYP121 (AtSYR1) is found on the PM of guard cells and may play a role in abscisic acid signaling |
| GO:0005886 plasma membrane | TAS PMID:11591731 Functional characterization of the KNOLLE-interacting t-SNAR... | ACCEPT | Summary: TAS to the AtSNAP33 paper (Heese et al. 2001), which proposes SNAP33 as a component of a general plasma-membrane SNARE complex but does not itself characterize SYP121. Reason: The location is correct; the cited paper is only indirectly relevant (it refers to candidate plasma membrane syntaxins and never names SYP121), so the support is the SYP121-specific statement from the SNARE genome survey. Supporting Evidence: PMID:11115874 AtSYP121 (AtSYR1) is found on the PM of guard cells and may play a role in abscisic acid signaling |
| GO:0006612 protein targeting to membrane | IDA PMID:17662029 Selective targeting of plasma membrane and tonoplast traffic... | MODIFY | Summary: From Tyrrell et al. 2007: dominant-negative Sp2 fragments of SYP121 selectively suppress secretion of secGFP to the plasma membrane. Reason: The experiment measures secretory traffic of a soluble marker to the plasma membrane, i.e. exocytosis, rather than targeting of a protein to a membrane. Exocytosis (GO:0006887) better describes the process in which SYP121 acts. Proposed replacements: exocytosis Supporting Evidence: PMID:17662029 we report here that traffic to the plasma membrane is suppressed selectively by Sp2 fragments of plasma membrane SNAREs AtSYP121 and AtSYP122 |
| GO:0006886 intracellular protein transport | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: SYP121 mediates post-Golgi delivery of membrane protein cargo (PIP aquaporins, KAT1 channels) to the plasma membrane. Reason: Correct at a general level (syntaxin family IBA), but intracellular protein transport is a consequence of vesicle fusion; the core process is exocytosis/vesicle fusion. Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0006886 intracellular protein transport | IDA PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | KEEP AS NON CORE | Summary: SYP121 mediates post-Golgi delivery of membrane protein cargo (PIP aquaporins, KAT1 channels) to the plasma membrane. Hachez et al. 2014 show PIP2;7 delivery depends on SYP121. Reason: Supported experimentally for PIP2;7 cargo; non-core relative to exocytosis. Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0006886 intracellular protein transport | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: SYP121 mediates post-Golgi delivery of membrane protein cargo (PIP aquaporins, KAT1 channels) to the plasma membrane. Reason: General family-level electronic inference; correct but non-core. Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0006886 intracellular protein transport | TAS PMID:11115874 The Arabidopsis genome. An abundance of soluble N-ethylmalei... | KEEP AS NON CORE | Summary: SYP121 mediates post-Golgi delivery of membrane protein cargo (PIP aquaporins, KAT1 channels) to the plasma membrane. Reason: Genome survey statement; correct but general. Supporting Evidence: PMID:11115874 One of the helices is always derived from a member of the syntaxin family of SNAREs, whereas the other two helices come from other types of SNAREs |
| GO:0006887 exocytosis | IBA GO_REF:0000033 | ACCEPT | Summary: SYP121 is the plasma-membrane Qa-SNARE for secretory vesicle fusion (exocytosis) in both constitutive secretion and focal immune secretion. Reason: Core process; IBA from plasma-membrane syntaxin clade and directly supported for SYP121 by secretion block with SYP121 dominant-negative fragments and by the PEN1-SNAP33-VAMP721/722 secretory complex. Supporting Evidence: PMID:32699172 The exo70A1 mutant affected SNARE distribution and suppressed vesicle traffic similarly to the dominant-negative truncated protein SYP121ΞC, which blocks secretion at the plasma membrane. PMID:18273019 The disease resistance function of the secretory PEN1-SNAP33-VAMP721/722 complex PMID:17662029 we report here that traffic to the plasma membrane is suppressed selectively by Sp2 fragments of plasma membrane SNAREs AtSYP121 and AtSYP122 |
| GO:0006906 vesicle fusion | IBA GO_REF:0000033 | ACCEPT | Summary: Vesicle fusion is the conserved process mediated by syntaxins. Reason: Core process consistent with the fusogenic MF; phylogenetically placed IBA. Supporting Evidence: PMID:11115874 One of the helices is always derived from a member of the syntaxin family of SNAREs, whereas the other two helices come from other types of SNAREs PMID:18678865 Our findings are consistent with the hypothesis that PEN1 acts in plant defense through the formation of ternary SNARE complexes |
| GO:0006952 defense response | TAS PMID:16255250 Potato homologs of Arabidopsis thaliana genes functional in ... | KEEP AS NON CORE | Summary: TAS from a potato study that selected Arabidopsis defense signaling genes for homolog mapping. Reason: PEN1 does contribute to antifungal defense (penetration resistance), so the broad term is not wrong, but the cited paper is a mapping study, and the more specific defense response to fungus annotation already captures this. Supporting Evidence: PMID:16255250 Nineteen Arabidopsis genes operating in defense signaling cascades were selected. PMID:15342780 PEN1 appears to have a basal function in secretion and a specialized defense-related function, being required for the polarized secretion events that give rise to papilla formation. |
| GO:0009504 cell plate | IDA PMID:21707889 Mechanisms of functional specificity among plasma-membrane s... | KEEP AS NON CORE | Summary: Cell plate localization from Reichardt et al. 2011, a promoter-swap study expressing PEN1 and other SYP1 syntaxins from the KNOLLE promoter. Reason: Likely reflects PEN1 expressed in dividing cells (possibly from the KNOLLE promoter); PEN1 could not substitute for KNOLLE in cytokinesis. Retained as a valid but non-core observation; the full text was not available to confirm the expression context. Supporting Evidence: PMID:21707889 Additionally, PEN1 could not substitute for KNOLLE because of SNARE domain differences, as revealed by protein chimeras. |
| GO:0009506 plasmodesma | HDA PMID:21533090 Arabidopsis plasmodesmal proteome. | KEEP AS NON CORE | Summary: Detected in a plasmodesmal-enriched proteome. Reason: Plasmodesmata are lined by plasma membrane, so detection of an abundant PM syntaxin is expected; no functional plasmodesmal role is known. Supporting Evidence: PMID:21533090 Arabidopsis plasmodesmal proteome. |
| GO:0009620 response to fungus | IMP PMID:15342780 The PEN1 syntaxin defines a novel cellular compartment upon ... | KEEP AS NON CORE | Summary: pen1 mutants allow increased penetration by non-adapted powdery mildew and show delayed papilla formation. Reason: Correct but less specific than defense response to fungus, which is retained as the defense-process annotation. Supporting Evidence: PMID:15342780 PEN1 appears to have a basal function in secretion and a specialized defense-related function, being required for the polarized secretion events that give rise to papilla formation. |
| GO:0009737 response to abscisic acid | IEP PMID:9915701 A tobacco syntaxin with a role in hormonal control of guard ... | KEEP AS NON CORE | Summary: Leyman et al. 1999 showed the tobacco ortholog Nt-SYR1 is needed for ABA control of guard-cell ion channels; the Arabidopsis transcript is ABA-inducible (UniProt induction note). Reason: IEP (expression response) for ABA is plausible; the cited abstract centers on the tobacco ortholog but the curator had the full text. Non-core; syp121 stomata close normally in ABA. Supporting Evidence: PMID:9915701 Disrupting Nt-Syr1 function by cleavage with Clostridium botulinum type C toxin or competition with a soluble fragment of Nt-Syr1 prevents potassium and chloride ion channel response to ABA in guard cells PMID:21914010 although stomata of the Arabidopsis syp121 loss-of-function mutant close normally in ABA and high CaΒ²βΊ |
| GO:0010119 regulation of stomatal movement | IMP PMID:21914010 The trafficking protein SYP121 of Arabidopsis connects progr... | KEEP AS NON CORE | Summary: syp121 mutants show delayed stomatal reopening after closure, linked to slowed K+ channel recycling. Reason: Physiological consequence of SYP121-dependent K+ channel traffic in guard cells; valid but non-core. Supporting Evidence: PMID:21914010 Our findings indicate that SYP121 facilitates stomatal reopening and they suggest that KβΊ channel traffic and recycling to the plasma membrane underpins the stress memory phenomenon of programmed closure in stomata. |
| GO:0010148 transpiration | IMP PMID:21914010 The trafficking protein SYP121 of Arabidopsis connects progr... | KEEP AS NON CORE | Summary: syp121 mutants show delayed rise in stomatal transpiration in the light. Reason: Whole-plant physiological outcome downstream of guard-cell membrane traffic; non-core. Supporting Evidence: PMID:21914010 Stomatal opening and the rise in stomatal transpiration of the mutant was delayed in the light and following CaΒ²βΊ-evoked closure |
| GO:0012505 endomembrane system | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA: syntaxins act in the endomembrane system. Reason: True but very general; SYP121 acts at the plasma membrane with a recycling endosomal pool. Supporting Evidence: PMID:21707889 syntaxin in innate immunity does not need upregulation of expression but instead requires pathogen-induced and endocytosis-dependent retargeting to the infection site. |
| GO:0016020 membrane | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Membrane from InterPro mapping. Reason: Correct but uninformative; plasma membrane is the specific location. Supporting Evidence: PMID:25082856 Among the plasma membrane-resident syntaxins, SYNTAXIN OF PLANTS121 (SYP121) is known to mediate the trafficking of vesicles between the Golgi complex and the plasma membrane |
| GO:0016192 vesicle-mediated transport | IEA GO_REF:0000002 | ACCEPT | Summary: Vesicle-mediated transport from InterPro SNARE domain mapping. Reason: Correct general process for a SNARE; exocytosis is the more specific core term. Supporting Evidence: PMID:25082856 Among the plasma membrane-resident syntaxins, SYNTAXIN OF PLANTS121 (SYP121) is known to mediate the trafficking of vesicles between the Golgi complex and the plasma membrane |
| GO:0016192 vesicle-mediated transport | IMP PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | ACCEPT | Summary: Hachez et al. 2014: SYP121 dominant-negative fragment and mutants impair vesicular delivery of PIPs to the plasma membrane. Reason: Experimentally supported for SYP121. Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0031201 SNARE complex | IBA GO_REF:0000033 | ACCEPT | Summary: SYP121 forms ternary SNARE complexes with SNAP33 and VAMP721/722 (and is associated with SYP61). Reason: Phylogenetic inference confirmed experimentally for SYP121. Supporting Evidence: PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0031201 SNARE complex | IDA PMID:25082856 Arabidopsis SNAREs SYP61 and SYP121 coordinate the trafficki... | ACCEPT | Summary: SYP121 forms ternary SNARE complexes with SNAP33 and VAMP721/722 (and is associated with SYP61). Hachez et al. 2014 propose a SYP61/SYP121 complex. Reason: Co-IP evidence supports SNARE complex membership. Supporting Evidence: PMID:25082856 Our results show that the post-Golgi traffic of PIP2;7 is mediated by both SYP61 and SYP121, which, together, form a previously unknown SNARE complex. |
| GO:0031201 SNARE complex | IDA PMID:32699172 Synergy among Exocyst and SNARE Interactions Identifies a Fu... | ACCEPT | Summary: SYP121 forms ternary SNARE complexes with SNAP33 and VAMP721/722 (and is associated with SYP61). Larson et al. 2020 show SYP121 in SNARE assemblies recruited to the exocyst. Reason: Consistent with extensive SNARE complex evidence. Supporting Evidence: PMID:32699172 exocyst EXO70 subunits bind preferentially to cognate plasma membrane SNAREs, notably SYP121 and VAMP721 |
| GO:0031201 SNARE complex | ISS PMID:14586469 SNARE-protein-mediated disease resistance at the plant cell ... | ACCEPT | Summary: SYP121 forms ternary SNARE complexes with SNAP33 and VAMP721/722 (and is associated with SYP61). ISS from barley ROR2, which forms a binary SNARE complex with SNAP34. Reason: Inference from a functional ortholog later confirmed directly for PEN1. Supporting Evidence: PMID:14586469 We show that resistance in barley requires a SNAP-25 (synaptosome-associated protein, molecular mass 25 kDa) homologue capable of forming a binary SNAP receptor (SNARE) complex with ROR2. PMID:18273019 plasma-membrane-resident PEN1 promiscuously forms SDS-resistant soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes together with the SNAP33 adaptor and a subset of vesicle-associated membrane proteins (VAMPs) |
| GO:0031348 negative regulation of defense response | IMP PMID:16732289 Conserved requirement for a plant host cell protein in powde... | KEEP AS NON CORE | Summary: Consonni et al. 2006 showed mlo2 resistance requires PEN1; Zhang et al. 2007 showed SYP121 with SYP122 negatively regulates SA, JA/ET and cell-death pathways (syp121 syp122 double mutants are necrotic with elevated SA). Reason: Genetic evidence for a negative regulatory effect on induced defenses exists, but it is described as distinct from the SNARE secretory function and is likely an indirect consequence of perturbed secretion/membrane homeostasis. Retained as non-core; the curator had the full text of the Consonni paper. Supporting Evidence: PMID:17241452 Thus SYP121 and SYP122 are negative regulators of PCD, SA, JA and ET pathways through a molecular function distinct from that of SYP121 in penetration resistance. |
| GO:0032940 secretion by cell | IDA PMID:32699172 Synergy among Exocyst and SNARE Interactions Identifies a Fu... | ACCEPT | Summary: Larson et al. 2020: SYP121ΞC blocks secretion at the plasma membrane. Reason: Correct; exocytosis is the more specific child term already accepted. Supporting Evidence: PMID:32699172 The exo70A1 mutant affected SNARE distribution and suppressed vesicle traffic similarly to the dominant-negative truncated protein SYP121ΞC, which blocks secretion at the plasma membrane. |
| GO:0043495 protein-membrane adaptor activity | IDA PMID:16531497 Selective mobility and sensitivity to SNAREs is exhibited by... | REMOVE | Summary: Sutter et al. 2006 report that SYP121 Sp2 fragments alter KAT1 delivery and mobility, and suggest SNAREs may contribute to positional anchoring of the channel. Reason: The authors explicitly state that their observations do not confirm a direct anchoring role or a direct SNARE-channel interaction, and the experiments relied mainly on the tobacco Sp2 fragment. SYP121 is a fusogenic SNARE, not a protein-membrane adaptor; its later-demonstrated direct K+ channel interaction regulates gating (captured by a NEW potassium channel regulator activity annotation). Supporting Evidence: PMID:16531497 These observations do not necessarily confirm an immediate role for the SNAREs in K + channel anchoring, nor do they imply direct proteinβprotein interaction between the SNARE and K + channel. PMID:19794113 SYP121 promoted gating of the inward-rectifying K + channel AKT1 but only when heterologously coexpressed with KC1. |
| GO:0050832 defense response to fungus | IGI PMID:15342780 The PEN1 syntaxin defines a novel cellular compartment upon ... | ACCEPT | Summary: Genetic interaction data (Assaad et al. 2004): pen1 syp122 double mutants and pen1 penetration resistance; PEN1 is recruited to papillae and drives polarized secretion at fungal penetration sites. Reason: PEN1 participates mechanistically, not merely by necessity: it is focally recruited beneath appressoria and, with SNAP33 and VAMP721/722, executes the secretory step of pre-invasive (penetration) resistance; SNARE-domain variants defective in ternary complex formation lose defense activity. Supporting Evidence: PMID:15342780 PEN1 appears to have a basal function in secretion and a specialized defense-related function, being required for the polarized secretion events that give rise to papilla formation. PMID:18273019 The disease resistance function of the secretory PEN1-SNAP33-VAMP721/722 complex PMID:18678865 Our findings are consistent with the hypothesis that PEN1 acts in plant defense through the formation of ternary SNARE complexes |
| GO:0061025 membrane fusion | TAS PMID:11115874 The Arabidopsis genome. An abundance of soluble N-ethylmalei... | ACCEPT | Summary: Membrane fusion is the general process driven by SNARE assembly. Reason: Correct; vesicle fusion is the more specific term. Supporting Evidence: PMID:11115874 One of the helices is always derived from a member of the syntaxin family of SNAREs, whereas the other two helices come from other types of SNAREs |
| GO:0072659 protein localization to plasma membrane | IMP PMID:21914010 The trafficking protein SYP121 of Arabidopsis connects progr... | KEEP AS NON CORE | Summary: Eisenach et al. 2012: KAT1 recycling to the plasma membrane after closure is slowed in syp121. Reason: Supported (K+ channel recycling to PM depends on SYP121) but a cargo-level consequence of exocytosis; non-core. Supporting Evidence: PMID:21914010 Our findings indicate that SYP121 facilitates stomatal reopening and they suggest that KβΊ channel traffic and recycling to the plasma membrane underpins the stress memory phenomenon of programmed closure in stomata. |
| GO:0072660 maintenance of protein location in plasma membrane | IMP PMID:21914010 The trafficking protein SYP121 of Arabidopsis connects progr... | KEEP AS NON CORE | Summary: Eisenach et al. 2012 (IMP) on KAT1 behaviour in syp121 guard cells. Reason: The abstract describes slowed KAT1 recycling rather than a defect in retaining KAT1 at the membrane; the full text may justify the term, so it is kept as non-core rather than removed. Supporting Evidence: PMID:21914010 Evoked stomatal closure was accompanied by internalisation of GFP-tagged KAT1 KβΊ channels in both wild-type and syp121 mutant guard cells, but their subsequently recycling was slowed in the mutant. |
| GO:0015459 potassium channel regulator activity | IDA PMID:19794113 A tripartite SNARE-K+ channel complex mediates in channel-de... | NEW | Summary: SYP121 binds the regulatory K+ channel subunit KC1 via its N-terminal FxRF motif, forms a tripartite complex with AKT1 and promotes AKT1/KC1 channel gating; syp121 roots lose KC1-associated inward K+ current. Reason: Direct binding plus electrophysiology in heterologous systems and Arabidopsis root epidermis show SYP121 itself modulates channel gating, separable from vesicle traffic (motif mutants). This is an activity of SYP121, not an indirect effect, and is not captured by any existing annotation (protein-membrane adaptor activity is removed). Supporting Evidence: PMID:19794113 SYP121 promoted gating of the inward-rectifying K + channel AKT1 but only when heterologously coexpressed with KC1. PMID:19794113 Here, we report that the Arabidopsis thaliana SNARE SYP121 binds to KC1, a regulatory K + channel subunit that assembles with different inward-rectifying K + channels to affect their activities. PMID:20884800 Analysis of channel gating thus showed the functional requirement for the FxRF motif of SYP121 to alter the gating of the K + channels. |
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Download this section (compressed HTML)Q: What cargo is delivered by PEN1-dependent focal secretion at papillae (callose synthase PMR4, cell-wall material, antimicrobial compounds, extracellular vesicles), and is any of it uniquely PEN1-dependent rather than shared with the PEN3/PEN2 pathway?
Q: Is the negative regulation of SA/JA/cell-death pathways seen in syp121 syp122 double mutants a direct signalling function or an indirect consequence of impaired secretion/membrane homeostasis?
Q: Should the SYP121 K+ channel interaction be modelled as potassium channel regulator activity at the plasma membrane, and does the SEC11-K+ channel binding exchange link it causally to SNARE assembly in planta?
Experiment: Proteomic profiling of PEN1-positive secretory vesicles/extracellular vesicles isolated from Bgh-challenged wild-type versus pen1 leaves to identify the defense cargo delivered by PEN1-dependent exocytosis.
Experiment: Express SNARE-motif or FxRF-motif SYP121 variants in syp121 syp122 backgrounds to separate fusion-dependent secretion, K+ channel gating and suppression of SA-dependent cell death.
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