BRI1 (BRASSINOSTEROID INSENSITIVE 1) is a leucine-rich repeat receptor kinase that serves as the primary receptor for brassinosteroid hormones in Arabidopsis thaliana. Located predominantly in the plasma membrane, BRI1 directly binds brassinolide (BL) with highest affinity, and less effectively castasterone (CS), through its extracellular domain containing 25 leucine-rich repeats interspersed with a unique ~70 amino acid island domain that is essential for high-affinity hormone binding. Upon hormone binding, BRI1 undergoes conformational changes that enable homodimerization and/or heterodimerization with co-receptors such as BAK1/SERK3, SERK1, and TTL in a kinase-dependent manner. This dimerization facilitates reciprocal transphosphorylation between intracellular kinase domains at critical residues including Y1052, Y1057, Y956, and Y1072. BRI1 possesses dual-specificity kinase activity, phosphorylating both serine/threonine and tyrosine residues on target proteins including BSK family kinases (BSK1, BSK2, BSK3, BSK5, BSK6, BSK8, BSK11), BAK1, SERK1, TTL, and itself through autophosphorylation. These phosphorylation events initiate a signaling cascade that ultimately activates transcription factors BZR1 and BES1, regulating gene expression programs controlling cell elongation, vascular differentiation, leaf development, flowering time, stress responses, and photomorphogenesis. BRI1 undergoes dynamic trafficking between plasma membrane and endosomal compartments where it forms heterodimeric complexes with BAK1, facilitating continued signaling or receptor turnover. The receptor may also possess guanylyl cyclase activity producing cyclic GMP as a secondary messenger. Loss-of-function mutations result in severe dwarfism, dark-green curled leaves, delayed flowering, and brassinosteroid insensitivity, while also affecting stress tolerance and light responses.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0038023 signaling receptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: BRI1 functions as a receptor that perceives brassinosteroid hormones and initiates signaling cascades. The deep research and structural studies confirm BRI1 acts as a signaling receptor. Reason: BRI1 is well-established as a receptor kinase that perceives brassinosteroid hormones. This annotation correctly captures its core function as a signaling receptor. Supporting Evidence: PMID:9298904 It encodes a ubiquitously expressed putative receptor kinase PMID:21666665 Plants however perceive steroids at membranes, using the membrane-integral receptor kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1) file:ARATH/BRI1/BRI1-deep-research-falcon.md The UniProt accession **O22476** corresponds to **Arabidopsis thaliana BRI1**, a **leucine-rich repeat receptor-like kinase (LRR-RLK)** that functions as the canonical **cell-surface brassinosteroid (BR) receptor** and signals with **SERK co-receptors** (notably **BAK1/AtSERK3**). |
| GO:0004674 protein serine/threonine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: BRI1 has dual-specificity kinase activity and phosphorylates serine/threonine residues on substrate proteins including BSKs, BAK1, and itself through autophosphorylation. Reason: Extensive biochemical evidence demonstrates that BRI1 has serine/threonine kinase activity. This is a core molecular function of the receptor. Supporting Evidence: PMID:18653891 The BSKs are phosphorylated by BRI1 in vitro and interact with BRI1 in vivo file:ARATH/BRI1/BRI1-falcon-research.md BRI1 phosphorylates BSK1, BSK2 and BSK3 in vitro. BRI1 phosphorylates BSK1, BSK3, BSK5, BSK6, BSK8 and BSK11 in vitro, demonstrating extensive BSK family phosphorylation. file:ARATH/BRI1/BRI1-deep-research-falcon.md Activated BRI1 phosphorylates RLCKs including BSK1 and CDG1; BSK1 is phosphorylated at Ser230, and CDG1 at Ser44, Ser47, and Ser234, with Ser234 important for CDG1 activation. |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: BRI1 is localized predominantly to the plasma membrane where it perceives extracellular brassinosteroid hormones. This localization is essential for its function as a hormone receptor. Reason: Multiple studies demonstrate that BRI1 localizes to the plasma membrane, which is essential for its role as a receptor for extracellular brassinosteroids. Supporting Evidence: PMID:10938344 BRI1 is localized in the plasma membrane file:ARATH/BRI1/BRI1-deep-research-falcon.md A 2024 synthesis emphasizes that BR perception and key early signaling steps occur at the **cell surface**, with BRI1 functioning as a PM receptor whose abundance and activity are tightly controlled. |
| GO:0009755 hormone-mediated signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: BRI1 mediates brassinosteroid hormone signaling pathways that control plant growth and development. This is a core biological process involving BRI1. Reason: BRI1 is the primary receptor for brassinosteroid hormones and mediates hormone-dependent signaling cascades. This annotation correctly captures its role in hormone signaling. Supporting Evidence: PMID:9298904 It encodes a ubiquitously expressed putative receptor kinase PMID:19124768 brassinosteroid insensitive 1 (BRI1), which is the BR receptor file:ARATH/BRI1/BRI1-deep-research-falcon.md **Brassinosteroids** are plant steroid hormones that regulate growth and development by being perceived at the **plasma membrane (PM)** by BRI1. |
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | MODIFY | Summary: As a protein kinase, BRI1 requires ATP binding for its catalytic activity. However, this term is quite general compared to the more specific ATP binding term. Reason: While BRI1 does bind nucleotides (specifically ATP), the more specific term ATP binding (GO:0005524) is more appropriate for a protein kinase. Proposed replacements: ATP binding Supporting Evidence: PMID:15935775 BRI1 is a ligand-independent homo-oligomer, as evidenced by the transphosphorylation of BRI1 kinase in vitro |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | ACCEPT | Summary: BRI1 has well-documented protein kinase activity. This is a core molecular function confirmed by extensive biochemical studies. Reason: BRI1 has dual-specificity protein kinase activity that phosphorylates both serine/threonine and tyrosine residues. This is a fundamental molecular function. Supporting Evidence: PMID:15935775 The leucine-rich-repeat receptor serine/threonine kinase, BRI1, is a cell-surface receptor for brassinosteroids |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is a duplicate of the IBA annotation above for the same GO term. BRI1 has confirmed serine/threonine kinase activity. Reason: BRI1 phosphorylates serine and threonine residues on target proteins. This annotation is supported by experimental evidence even though this instance is IEA. Supporting Evidence: PMID:15935775 leucine-rich-repeat receptor serine/threonine kinase PMID:18653891 The BSKs are phosphorylated by BRI1 in vitro |
| GO:0004713 protein tyrosine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: BRI1 has dual-specificity kinase activity and can phosphorylate tyrosine residues in addition to serine/threonine residues. Reason: Studies have shown that BRI1 has tyrosine kinase activity as part of its dual-specificity kinase function. It phosphorylates tyrosine residues on target proteins. Supporting Evidence: PMID:19124768 Tyrosine phosphorylation of the BRI1 receptor kinase emerges as a component of brassinosteroid signaling file:ARATH/BRI1/BRI1-falcon-research.md BRI1 has dual-specificity kinase activity acting on both serine/threonine- and tyrosine-containing substrates. Critical phosphorylation sites (Y1052, Y1057, Y956, and Y1072) have been identified within the catalytic domain. |
| GO:0004714 transmembrane receptor protein tyrosine kinase activity | IEA GO_REF:0000003 | MODIFY | Summary: While BRI1 is a transmembrane receptor with some tyrosine kinase activity, this term is primarily used for animal receptor tyrosine kinases. BRI1 is better described as a transmembrane receptor serine/threonine kinase with dual specificity. The precise term transmembrane receptor protein serine/threonine kinase activity (GO:0004675) captures both the receptor and the predominant Ser/Thr kinase character. Reason: This term is typically applied to animal receptor tyrosine kinases. BRI1 is primarily a serine/threonine kinase with some tyrosine kinase activity, making the transmembrane receptor protein serine/threonine kinase term (GO:0004675) the most appropriate single replacement, with protein serine/threonine kinase activity (GO:0004674) as a more general alternative. Proposed replacements: transmembrane receptor protein serine/threonine kinase activity protein serine/threonine kinase activity Supporting Evidence: PMID:19124768 Both proteins are classified as serine/threonine protein kinases, but [...] recombinant cytoplasmic domains of BRI1 and BAK1 also autophosphorylate on tyrosine residues and thus are dual-specificity kinases file:ARATH/BRI1/BRI1-deep-research-falcon.md BRI1 is a receptor kinase primarily classified as a Ser/Thr kinase, but it also displays **tyrosine phosphorylation** (dual-specificity behavior) as part of BR signaling regulatory logic. |
| GO:0005496 steroid binding | IEA GO_REF:0000043 | MODIFY | Summary: BRI1 directly binds brassinosteroids (steroid hormones) through its extracellular island domain. The more specific child term brassinosteroid binding (GO:0090411) precisely captures the bound ligand and is preferred over the generic steroid binding term. Reason: BRI1 binds brassinolide and other brassinosteroids with high affinity via the island domain/LRR22 pocket. The substrate-specific term brassinosteroid binding (GO:0090411) is more informative than the generic steroid binding (GO:0005496), which would also encompass animal steroids that BRI1 does not bind (e.g., ecdysone). Proposed replacements: brassinosteroid binding Supporting Evidence: PMID:15650741 first evidence for direct binding of active brassinosteroids to BRI1 using a biotin-tagged photoaffinity castasterone PMID:21666665 A 70 amino-acid island domain between LRRs 21 and 22 folds back into the interior of the superhelix to create a surface pocket for binding the plant hormone brassinolide file:ARATH/BRI1/BRI1-falcon-research.md BRI1 binds brassinolide (BL), and less effectively castasterone (CS), but not 2,3,22,23-O-tetramethylbrassinolide or ecdysone. The extracellular region contains numerous leucine-rich repeats interspersed with a unique island domain essential for high-affinity BL binding. file:ARATH/BRI1/BRI1-deep-research-falcon.md BRI1 is a **cell-surface LRR-RLK** whose ectodomain contains an **island domain** that participates directly in steroid binding; work on early BR signaling established that the **island domain together with LRR22** forms the steroid-binding motif. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: As a protein kinase, BRI1 requires ATP binding for its phosphorylation activity. This is an essential molecular function for kinase activity. Reason: Protein kinases require ATP binding for their catalytic activity. BRI1's kinase function depends on ATP as a phosphate donor. Supporting Evidence: PMID:16857903 BKI1 is a substrate of BRI1 kinase |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: This is another annotation for plasma membrane localization (duplicate of IBA annotation above). BRI1 localizes to the plasma membrane. Reason: BRI1 is well-documented to localize to the plasma membrane where it functions as a hormone receptor. This annotation is correct. Supporting Evidence: PMID:10938344 BRI1 is localized in the plasma membrane |
| GO:0008289 lipid binding | IEA GO_REF:0000043 | REMOVE | Summary: While brassinosteroids have steroid backbone structures, they are classified as steroid hormones rather than lipids. The steroid binding term is more specific and appropriate. Reason: This annotation is likely an over-annotation. BRI1 binds steroid hormones (brassinosteroids), not general lipids. The more specific steroid binding annotation is appropriate. Supporting Evidence: PMID:21666665 A 70-amino-acid island domain between LRRs 21 and 22 folds back into the interior of the superhelix to create a surface pocket for binding the plant hormone brassinolide |
| GO:0009416 response to light stimulus | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: BRI1 is involved in light responses indirectly through its role in brassinosteroid signaling which affects photomorphogenesis and light-regulated gene expression. Reason: While BRI1 is involved in light responses, this is not a core function but rather a downstream consequence of brassinosteroid signaling affecting light-regulated developmental processes. |
| GO:0009742 brassinosteroid mediated signaling pathway | IEA GO_REF:0000120 | ACCEPT | Summary: This is the most specific and accurate biological process annotation for BRI1. It is the central receptor for brassinosteroid signaling. Reason: BRI1 is the primary receptor that mediates brassinosteroid signaling pathways. This is its core biological process function. Supporting Evidence: PMID:9298904 It encodes a ubiquitously expressed putative receptor kinase PMID:19124768 brassinosteroid insensitive 1 (BRI1), which is the BR receptor file:ARATH/BRI1/BRI1-deep-research-falcon.md In Arabidopsis, BRI1 forms a complex with a **SERK family co-receptor**, especially **BAK1/AtSERK3**, and the complex becomes active through **sequential transphosphorylation** between the two kinase domains. |
| GO:0009791 post-embryonic development | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: BRI1 is involved in post-embryonic development through its role in controlling cell elongation, leaf development, and flowering. However, this is quite broad. Reason: While BRI1 affects post-embryonic development, this is a very general term. BRI1's role is more specifically in brassinosteroid-mediated developmental processes. |
| GO:0010008 endosome membrane | IEA GO_REF:0000044 | ACCEPT | Summary: BRI1 traffics from the plasma membrane to endosomes after ligand binding and activation. This is part of its dynamic localization. Reason: Studies show that BRI1 undergoes endocytosis and localizes to endosomal compartments after brassinosteroid binding, where it continues signaling. Supporting Evidence: PMID:15548744 BRI1 and AtSERK3 preferentially heterodimerize in the endosomes [...] Coexpression of BRI1 and AtSERK3 results in [...] accelerated endocytosis |
| GO:0016301 kinase activity | IEA GO_REF:0000043 | MODIFY | Summary: BRI1 has kinase activity. However, the more specific protein kinase activity term is more appropriate since BRI1 phosphorylates proteins. Reason: While BRI1 has kinase activity, the more specific term 'protein kinase activity' (GO:0004672) better describes its function as it specifically phosphorylates proteins. Proposed replacements: protein kinase activity |
| GO:0016740 transferase activity | IEA GO_REF:0000043 | MODIFY | Summary: Kinases are transferases that transfer phosphate groups from ATP to target proteins. However, this term is too general compared to the specific kinase activity terms. Reason: While technically correct (kinases are transferases), this term is too general. The more specific protein kinase activity terms better describe BRI1's function. Proposed replacements: protein kinase activity |
| GO:0106310 protein serine kinase activity | IEA GO_REF:0000116 | ACCEPT | Summary: BRI1 phosphorylates serine residues on target proteins. This is a specific component of its dual-specificity kinase activity. Reason: BRI1 has serine kinase activity as part of its dual-specificity kinase function. It phosphorylates serine residues on various substrate proteins. Supporting Evidence: PMID:15935775 Autoregulation and homodimerization are involved in the activation of the plant steroid receptor BRI1 PMID:18653891 The BSKs are phosphorylated by BRI1 in vitro |
| GO:0005515 protein binding | IPI PMID:12150928 BRI1/BAK1, a receptor kinase pair mediating brassinosteroid ... | MARK AS OVER ANNOTATED | Summary: This study demonstrates BRI1 interaction with BAK1, a key co-receptor. While protein binding is general, the IPI evidence supports specific protein-protein interactions. Reason: This is based on experimental evidence (IPI) showing BRI1 interactions with specific binding partners like BAK1. The protein binding annotation is appropriate for documented protein-protein interactions. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:12150928 BRI1/BAK1, a receptor kinase pair mediating brassinosteroid signaling |
| GO:0005515 protein binding | IPI PMID:15319482 The Arabidopsis transthyretin-like protein is a potential su... | MARK AS OVER ANNOTATED | Summary: This study shows BRI1 interaction with TTL (Transthyretin-Like protein), a potential substrate. IPI evidence supports protein binding annotation. Reason: Experimental evidence shows BRI1 binds to and phosphorylates TTL protein. The protein binding annotation is supported by direct interaction studies. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:15319482 The Arabidopsis transthyretin-like protein is a potential substrate of BRASSINOSTEROID-INSENSITIVE 1 |
| GO:0005515 protein binding | IPI PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 ... | MARK AS OVER ANNOTATED | Summary: This study demonstrates BRI1 is part of the SERK1 protein complex. IPI evidence supports protein binding annotation. Reason: Experimental evidence shows BRI1 forms protein complexes with SERK family proteins. The protein binding annotation is supported by complex formation studies. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 protein complex includes BRASSINOSTEROID-INSENSITIVE1 |
| GO:0005515 protein binding | IPI PMID:18653891 BSKs mediate signal transduction from the receptor kinase BR... | MARK AS OVER ANNOTATED | Summary: This study shows BRI1 interactions with BSK proteins (BSK1, BSK2, BSK3) which mediate signal transduction. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 binds to and phosphorylates BSK proteins as part of the signaling cascade. Direct protein interactions are documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:18653891 The BSKs are phosphorylated by BRI1 in vitro and interact with BRI1 in vivo |
| GO:0005515 protein binding | IPI PMID:22087006 Brassinosteroids inhibit pathogen-associated molecular patte... | MARK AS OVER ANNOTATED | Summary: This study examines BRI1 interactions in the context of immune signaling. IPI evidence supports protein binding. Reason: Experimental evidence of BRI1 protein interactions in immune signaling pathways. The protein binding annotation is supported by interaction studies. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:22087006 the LRR-RLK BRI1 in brassinosteroid (BR)-mediated growth |
| GO:0005515 protein binding | IPI PMID:22184234 Deactivation of the Arabidopsis BRASSINOSTEROID INSENSITIVE ... | MARK AS OVER ANNOTATED | Summary: This study focuses on BRI1 autophosphorylation and protein interactions within the glycine-rich loop. IPI evidence supports protein binding. Reason: Study demonstrates protein binding interactions related to BRI1 autophosphorylation and receptor regulation. Direct protein interactions documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:22184234 Deactivation of the Arabidopsis BRASSINOSTEROID INSENSITIVE 1 (BRI1) receptor kinase by autophosphorylation within the glycine-rich loop |
| GO:0005515 protein binding | IPI PMID:23929946 Molecular mechanism for plant steroid receptor activation by... | MARK AS OVER ANNOTATED | Summary: This study examines molecular mechanisms of plant steroid receptor activation by co-receptor kinases. IPI evidence supports protein binding. Reason: Study demonstrates protein binding interactions between BRI1 and co-receptor kinases essential for receptor activation. Direct experimental evidence. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:23929946 Molecular mechanism for plant steroid receptor activation by somatic embryogenesis co-receptor kinases |
| GO:0005515 protein binding | IPI PMID:29320478 An extracellular network of Arabidopsis leucine-rich repeat ... | MARK AS OVER ANNOTATED | Summary: This study describes an extracellular network of Arabidopsis leucine-rich repeat receptor kinases. IPI evidence supports protein binding. Reason: Study demonstrates BRI1 participation in protein interaction networks with other receptor kinases. Experimental evidence of protein binding. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:29320478 An extracellular network of Arabidopsis leucine-rich repeat receptor kinases |
| GO:0042802 identical protein binding | IPI PMID:15935775 Autoregulation and homodimerization are involved in the acti... | ACCEPT | Summary: This study demonstrates BRI1 homodimerization, showing that BRI1 can bind to itself (identical protein binding). This is important for receptor activation. Reason: Experimental evidence shows BRI1 can form homodimers, which is essential for receptor activation. The identical protein binding annotation accurately describes this interaction. Supporting Evidence: PMID:15935775 Autoregulation and homodimerization are involved in the activation of the plant steroid receptor BRI1 |
| GO:0042802 identical protein binding | IPI PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 ... | ACCEPT | Summary: This study also demonstrates BRI1's ability to bind to identical copies of itself as part of complex formation. IPI evidence supports identical protein binding. Reason: Experimental evidence confirms BRI1 homodimerization as part of its activation mechanism. Multiple studies support this identical protein binding activity. Supporting Evidence: PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 protein complex includes BRASSINOSTEROID-INSENSITIVE1. |
| GO:0042802 identical protein binding | IPI PMID:22184234 Deactivation of the Arabidopsis BRASSINOSTEROID INSENSITIVE ... | ACCEPT | Summary: This study examines BRI1 autophosphorylation which involves homodimerization and identical protein binding. IPI evidence supports this annotation. Reason: Study shows BRI1 homodimerization is involved in autophosphorylation and receptor regulation. Experimental evidence supports identical protein binding. Supporting Evidence: PMID:22184234 Deactivation of the Arabidopsis BRASSINOSTEROID INSENSITIVE 1 (BRI1) receptor kinase by autophosphorylation within the glycine-rich loop |
| GO:0001578 microtubule bundle formation | IEA GO_REF:0000107 | REMOVE | Summary: This annotation appears to be an over-annotation. BRI1 is not directly involved in microtubule bundle formation but rather in brassinosteroid signaling. Reason: There is no evidence that BRI1 is directly involved in microtubule bundle formation. This appears to be an incorrect computational annotation that should be removed. |
| GO:0009647 skotomorphogenesis | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: BRI1 affects skotomorphogenesis (dark growth) through brassinosteroid signaling that regulates hypocotyl elongation and other dark-growth responses. Reason: While BRI1 influences skotomorphogenesis through brassinosteroid signaling affecting hypocotyl elongation, this is not a core function but a downstream developmental consequence. |
| GO:0009729 detection of brassinosteroid stimulus | IEA GO_REF:0000120 | ACCEPT | Summary: This is a duplicate of the IMP annotation above for the same term. BRI1's primary function is to detect brassinosteroid stimuli. Reason: This annotation correctly describes BRI1's core function - detecting brassinosteroid stimuli. Even though this is IEA evidence, the annotation is accurate and supported by experimental data. Supporting Evidence: PMID:9298904 A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction |
| GO:0000149 SNARE binding | IPI PMID:38036295 R-SNARE protein YKT61 mediates root apical meristem cell div... | ACCEPT | Summary: This recent study shows BRI1 interaction with SNARE protein YKT61 involved in receptor recycling. This is a specific protein binding function. Reason: Experimental evidence demonstrates BRI1 binds to YKT61 SNARE protein as part of receptor recycling mechanisms. This is a specific and well-documented interaction. Supporting Evidence: PMID:38036295 R-SNARE protein YKT61 mediates root apical meristem cell division via BRASSINOSTEROID-INSENSITIVE1 recycling |
| GO:0009414 response to water deprivation | IMP PMID:36508461 A role for brassinosteroid signalling in decision-making pro... | KEEP AS NON CORE | Summary: This study shows BRI1's role in water deprivation responses through brassinosteroid signaling. However, this is not a core function but a downstream consequence. Reason: While BRI1 is involved in stress responses including water deprivation through brassinosteroid signaling, this is not its primary function but rather a downstream consequence of BR signaling affecting stress tolerance. Supporting Evidence: PMID:36508461 A role for brassinosteroid signalling in decision-making processes in the Arabidopsis seedling |
| GO:0009416 response to light stimulus | IMP PMID:36508461 A role for brassinosteroid signalling in decision-making pro... | KEEP AS NON CORE | Summary: This is a duplicate of the IEA annotation above. BRI1 affects light responses through brassinosteroid signaling but this is not a core function. Reason: BRI1 influences light responses through brassinosteroid signaling pathways that affect photomorphogenesis, but this is not its primary molecular function. Supporting Evidence: PMID:36508461 eCollection 2022 Dec. |
| GO:0090351 seedling development | IMP PMID:17600708 BAK1 and BKK1 regulate brassinosteroid-dependent growth and ... | KEEP AS NON CORE | Summary: BRI1 plays a role in seedling development through brassinosteroid signaling. This is one of many pleiotropic developmental outcomes downstream of BR signaling rather than a core molecular function. Reason: BRI1 influences seedling development through brassinosteroid-mediated control of cell elongation and growth, but this is a downstream developmental consequence of its core role as the plasma-membrane BR receptor kinase, not a core function in itself. BRI1 is highly pleiotropic, so broad developmental terms are best retained as non-core. Supporting Evidence: PMID:17600708 BAK1 and BKK1 regulate brassinosteroid-dependent growth and brassinosteroid-independent cell-death pathways |
| GO:0042803 protein homodimerization activity | IPI PMID:15650741 Binding of brassinosteroids to the extracellular domain of p... | ACCEPT | Summary: This study demonstrates BRI1's ability to homodimerize, which is essential for receptor activation after brassinosteroid binding. Reason: Experimental evidence shows BRI1 homodimerization is critical for receptor activation. This molecular function is well-documented and essential for BRI1's activity. Supporting Evidence: PMID:15650741 Binding of brassinosteroids to the extracellular domain of plant receptor kinase BRI1 |
| GO:0032991 protein-containing complex | IPI PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 ... | ACCEPT | Summary: BRI1 forms multiprotein complexes with SERK proteins, BAK1, and other signaling components. This is a cellular component annotation. Reason: Experimental evidence demonstrates BRI1 is part of larger protein complexes essential for brassinosteroid signaling. Complex formation is well-documented. Supporting Evidence: PMID:16473966 The Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 protein complex includes BRASSINOSTEROID-INSENSITIVE1 |
| GO:0005886 plasma membrane | HDA PMID:16618929 Mapping the Arabidopsis organelle proteome. | ACCEPT | Summary: This annotation comes from high-throughput organelle proteomics mapping studies. It provides additional evidence for BRI1's plasma membrane localization. Reason: High-throughput direct assay (HDA) evidence supports BRI1's plasma membrane localization from organelle proteome mapping. This confirms other localization studies. Supporting Evidence: PMID:16618929 Mapping the Arabidopsis organelle proteome |
| GO:0005886 plasma membrane | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | ACCEPT | Summary: This annotation comes from LOPIT proteomics studies of plant Golgi apparatus proteins, providing additional high-throughput evidence for subcellular localization. Reason: High-throughput proteomics evidence (HDA) from LOPIT studies supports BRI1's membrane localization. Multiple independent studies confirm plasma membrane localization. Supporting Evidence: PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatus proteins are revealed by LOPIT proteomics |
| GO:0005515 protein binding | IPI PMID:32176351 Putrescine metabolism modulates the biphasic effects of bras... | MARK AS OVER ANNOTATED | Summary: This study examines protein interactions in the context of putrescine metabolism and brassinosteroid effects on salt tolerance. IPI evidence supports protein binding. Reason: Experimental evidence of protein interactions involving BRI1 in stress response pathways. The protein binding annotation is supported. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:32176351 Putrescine metabolism modulates the biphasic effects of brassinosteroids on canola and Arabidopsis salt tolerance. |
| GO:0005886 plasma membrane | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | ACCEPT | Summary: This annotation comes from protein correlation profiling studies analyzing membrane-associated protein oligomerization. Reason: High-throughput correlation profiling (HDA) provides additional evidence for BRI1's membrane association and oligomerization behavior. Supports plasma membrane localization. Supporting Evidence: PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerization Using Protein Correlation Profiling |
| GO:0005515 protein binding | IPI PMID:23496207 BSKs are partially redundant positive regulators of brassino... | MARK AS OVER ANNOTATED | Summary: This study shows BSKs are positive regulators of brassinosteroid signaling and interact with BRI1. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 binds to BSK proteins as part of brassinosteroid signaling cascade. Direct protein interactions documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:23496207 BSKs are partially redundant positive regulators of brassinosteroid signaling in Arabidopsis |
| GO:0005515 protein binding | IPI PMID:26517938 The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switch... | MARK AS OVER ANNOTATED | Summary: This study shows BRI1 is switched off by PP2A phosphatases, demonstrating protein interactions with regulatory phosphatases. IPI evidence supports protein binding. Reason: Experimental evidence shows BRI1 interacts with PP2A phosphatase subunits for receptor regulation. Direct protein binding demonstrated. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:26517938 The Brassinosteroid-Activated BRI1 Receptor Kinase Is Switched off by Dephosphorylation Mediated by Cytoplasm-Localized PP2A B' Subunits |
| GO:0005515 protein binding | IPI PMID:21855796 The CDG1 kinase mediates brassinosteroid signal transduction... | MARK AS OVER ANNOTATED | Summary: This study shows CDG1 kinase mediates signal transduction from BRI1, demonstrating protein interactions in the signaling cascade. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 interacts with CDG1 kinase as part of the brassinosteroid signaling pathway. Direct protein interactions documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:21855796 The CDG1 kinase mediates brassinosteroid signal transduction from BRI1 receptor kinase to BSU1 phosphatase and GSK3-like kinase BIN2 |
| GO:0005515 protein binding | IPI PMID:23818580 Inverse modulation of plant immune and brassinosteroid signa... | MARK AS OVER ANNOTATED | Summary: This study shows BIK1 inverse modulation of plant immune and brassinosteroid signaling, demonstrating BRI1-BIK1 protein interactions. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 interacts with BIK1 kinase in both immune and brassinosteroid signaling pathways. Direct protein interactions documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:23818580 Inverse modulation of plant immune and brassinosteroid signaling pathways by the receptor-like cytoplasmic kinase BIK1 |
| GO:0005496 steroid binding | IDA PMID:21666665 Structural basis of steroid hormone perception by the recept... | MODIFY | Summary: This is a duplicate of the IEA annotation above but with IDA evidence. The structural study provides direct evidence for brassinosteroid binding to BRI1. As with the IEA instance, the more specific child term brassinosteroid binding (GO:0090411) is preferred over the generic steroid binding term. Reason: Supported by direct structural evidence (IDA) of brassinolide binding in the island-domain pocket. The substrate-specific term brassinosteroid binding (GO:0090411) better reflects the demonstrated ligand specificity than the generic steroid binding (GO:0005496). Proposed replacements: brassinosteroid binding Supporting Evidence: PMID:21666665 Structural basis of steroid hormone perception by the receptor kinase BRI1 |
| GO:0048366 leaf development | IMP PMID:20460583 Increased leaf size: different means to an end. | KEEP AS NON CORE | Summary: BRI1 influences leaf development through brassinosteroid-mediated regulation of cell expansion and leaf morphology. This is a pleiotropic downstream developmental outcome rather than a core function. Reason: BRI1 affects leaf development through brassinosteroid signaling that controls cell elongation and leaf size, but this is one of many downstream developmental consequences of its core role as the BR receptor kinase. For a highly pleiotropic receptor, such broad developmental terms are best retained as non-core. Supporting Evidence: PMID:20460583 Increased leaf size: different means to an end |
| GO:0010584 pollen exine formation | IMP PMID:20231470 Brassinosteroids control male fertility by regulating the ex... | KEEP AS NON CORE | Summary: BRI1 regulates male fertility and pollen development including exine formation through brassinosteroid signaling. This is a specific developmental process. Reason: While BRI1 affects pollen exine formation through brassinosteroid signaling in reproductive development, this is a specialized developmental process rather than a core function. Supporting Evidence: PMID:20231470 brassinosteroids control male fertility at least in part via directly regulating key genes for anther and pollen development in Arabidopsis |
| GO:0048657 anther wall tapetum cell differentiation | IMP PMID:20231470 Brassinosteroids control male fertility by regulating the ex... | KEEP AS NON CORE | Summary: BRI1 regulates anther development and tapetum cell differentiation through brassinosteroid signaling in male reproductive development. Reason: While BRI1 affects anther wall tapetum cell differentiation through brassinosteroid signaling, this is a very specialized reproductive developmental process rather than a core function. Supporting Evidence: PMID:20231470 Brassinosteroids control male fertility by regulating the expression of key genes involved in Arabidopsis anther and pollen development |
| GO:0005515 protein binding | IPI PMID:19452453 Proteomic profiling of tandem affinity purified 14-3-3 prote... | MARK AS OVER ANNOTATED | Summary: This study involves proteomic profiling of 14-3-3 protein complexes, showing BRI1 interactions with 14-3-3 proteins. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 interacts with 14-3-3 proteins as part of regulatory complexes. Direct protein binding documented through proteomic approaches. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:19452453 Proteomic profiling of tandem affinity purified 14-3-3 protein complexes in Arabidopsis thaliana |
| GO:0009742 brassinosteroid mediated signaling pathway | IMP PMID:19124768 Tyrosine phosphorylation of the BRI1 receptor kinase emerges... | ACCEPT | Summary: This is another annotation for the same term as the IEA annotation above, but with IMP evidence. BRI1 is the central receptor for brassinosteroid signaling. Reason: This annotation has experimental evidence (IMP) supporting BRI1's core function as the receptor mediating brassinosteroid signaling pathways. This is the most accurate biological process term for BRI1. Supporting Evidence: PMID:19124768 Tyrosine phosphorylation of the BRI1 receptor kinase emerges as a component of brassinosteroid signaling in Arabidopsis |
| GO:0005886 plasma membrane | IDA PMID:19004783 Differential degradation of PIN2 auxin efflux carrier by ret... | ACCEPT | Summary: This is another annotation for plasma membrane localization with IDA evidence. BRI1 localizes to the plasma membrane where it functions as a hormone receptor. Reason: Direct experimental evidence (IDA) confirms BRI1's plasma membrane localization, which is essential for its function as a brassinosteroid receptor. This is correct. Supporting Evidence: PMID:19004783 Differential degradation of PIN2 auxin efflux carrier by retromer-dependent vacuolar targeting. |
| GO:0010224 response to UV-B | IGI PMID:15474373 Ultraviolet-B signalling: Arabidopsis brassinosteroid mutant... | KEEP AS NON CORE | Summary: This study shows brassinosteroid mutants are defective in UV-B regulated defence gene expression, indicating BRI1's role in UV-B responses. Reason: While BRI1 affects UV-B responses through brassinosteroid signaling pathways, this is not a core function but rather a consequence of BR signaling affecting stress responses. Supporting Evidence: PMID:15474373 Ultraviolet-B signalling: Arabidopsis brassinosteroid mutants are defective in UV-B regulated defence gene expression |
| GO:0005515 protein binding | IPI PMID:12150929 BAK1, an Arabidopsis LRR receptor-like protein kinase, inter... | MARK AS OVER ANNOTATED | Summary: This study demonstrates BAK1 LRR receptor-like protein kinase interacts with BRI1 and modulates brassinosteroid signaling. IPI evidence supports protein binding. Reason: Experimental evidence shows direct interaction between BRI1 and BAK1, which is essential for brassinosteroid signaling. Well-documented protein binding. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:12150929 BAK1, an Arabidopsis LRR receptor-like protein kinase, interacts with BRI1 and modulates brassinosteroid signaling |
| GO:0005515 protein binding | IPI PMID:15935775 Autoregulation and homodimerization are involved in the acti... | MARK AS OVER ANNOTATED | Summary: This study demonstrates autoregulation and homodimerization of BRI1, showing protein binding through self-interaction. IPI evidence supports protein binding. Reason: Experimental evidence shows BRI1 self-association and homodimerization as part of receptor activation. Direct protein binding demonstrated. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:15935775 Autoregulation and homodimerization are involved in the activation of the plant steroid receptor BRI1 |
| GO:0005515 protein binding | IPI PMID:15998311 Interaction of Arabidopsis BRASSINOSTEROID-INSENSITIVE 1 rec... | MARK AS OVER ANNOTATED | Summary: This study shows BRI1 interaction with a homolog of mammalian TGF-beta receptor interacting protein. IPI evidence supports protein binding. Reason: Experimental evidence demonstrates BRI1 binds to TGF-beta receptor-like interacting proteins, expanding the interaction network. Direct protein binding documented. However, GO:0005515 protein binding is an uninformative parent molecular function term; the specific, informative aspects of this interaction (co-receptor/homodimer binding, complex membership, and substrate phosphorylation) are captured by the dedicated kinase, identical/heterodimerization, and protein-containing complex annotations already in this review, so the generic protein binding annotation is marked as over-annotated. Supporting Evidence: PMID:15998311 Interaction of Arabidopsis BRASSINOSTEROID-INSENSITIVE 1 receptor kinase with a homolog of mammalian TGF-beta receptor interacting protein |
| GO:0009911 positive regulation of flower development | IGI PMID:17611230 Attenuation of brassinosteroid signaling enhances FLC expres... | KEEP AS NON CORE | Summary: This study shows attenuation of brassinosteroid signaling enhances FLC expression and delays flowering, indicating BRI1 indirectly promotes flowering through BR signaling. This is a pleiotropic downstream outcome. Reason: Genetic evidence (IGI) links reduced BR signaling to delayed flowering, but BRI1's effect on flower development is an indirect, downstream consequence of its core role as the BR receptor kinase rather than a core function. For this pleiotropic receptor such developmental terms are best retained as non-core. Supporting Evidence: PMID:17611230 Attenuation of brassinosteroid signaling enhances FLC expression and delays flowering |
| GO:0004672 protein kinase activity | IDA PMID:16857903 Brassinosteroids regulate dissociation of BKI1, a negative r... | ACCEPT | Summary: This is another annotation for protein kinase activity with direct experimental evidence (IDA). BRI1 has well-documented kinase activity. Reason: Direct experimental evidence (IDA) confirms BRI1's protein kinase activity, which is a core molecular function essential for brassinosteroid signaling. Supporting Evidence: PMID:16857903 Brassinosteroids regulate dissociation of BKI1, a negative regulator of BRI1 signaling, from the plasma membrane |
| GO:0010268 brassinosteroid homeostasis | IEP PMID:15908602 Brassinosteroid homeostasis in Arabidopsis is ensured by fee... | KEEP AS NON CORE | Summary: BRI1 is indirectly involved in brassinosteroid homeostasis through feedback regulation. When BR signaling is impaired, BR biosynthesis is upregulated. This is an emergent feedback property, not a core function. Reason: BR homeostasis arises as a transcriptional feedback consequence of BRI1 signaling output (BR biosynthesis genes are upregulated when signaling is impaired) rather than being a direct activity of BRI1. The IEP evidence reflects an expression/correlation pattern, so this is best retained as a non-core downstream regulatory role. Supporting Evidence: PMID:15908602 Brassinosteroid homeostasis in Arabidopsis is ensured by feedback expressions of multiple genes involved in its metabolism |
| GO:0004674 protein serine/threonine kinase activity | IDA PMID:15935775 Autoregulation and homodimerization are involved in the acti... | ACCEPT | Summary: This is another annotation for protein serine/threonine kinase activity with direct experimental evidence (IDA). BRI1 has confirmed dual-specificity kinase activity. Reason: Direct experimental evidence (IDA) confirms BRI1's serine/threonine kinase activity, which is a core molecular function essential for phosphorylating substrate proteins. Supporting Evidence: PMID:15935775 The leucine-rich-repeat receptor serine/threonine kinase, BRI1, is a cell-surface receptor for brassinosteroids |
| GO:0005768 endosome | IDA PMID:15548744 Heterodimerization and endocytosis of Arabidopsis brassinost... | ACCEPT | Summary: BRI1 undergoes endocytosis and localizes to endosomes after ligand binding. This is part of its dynamic trafficking and signaling regulation. Reason: Direct experimental evidence (IDA) shows BRI1 localizes to endosomes after internalization. This is an important aspect of receptor trafficking and signaling regulation. Supporting Evidence: PMID:15548744 Heterodimerization and endocytosis of Arabidopsis brassinosteroid receptors BRI1 and AtSERK3 (BAK1) |
| GO:0005886 plasma membrane | IDA PMID:10938344 Brassinosteroid-insensitive-1 is a ubiquitously expressed le... | ACCEPT | Summary: This is another annotation for plasma membrane localization with IDA evidence from the original BRI1 characterization study. Reason: Direct experimental evidence (IDA) from the foundational BRI1 study confirms plasma membrane localization, which is essential for its receptor function. Supporting Evidence: PMID:10938344 Brassinosteroid-insensitive-1 is a ubiquitously expressed leucine-rich repeat receptor serine/threonine kinase |
| GO:0009729 detection of brassinosteroid stimulus | IMP PMID:9298904 A putative leucine-rich repeat receptor kinase involved in b... | ACCEPT | Summary: This annotation describes BRI1's most fundamental biological process - detecting brassinosteroid hormones. This is from the original BRI1 characterization study. Reason: BRI1's primary function is to detect brassinosteroid stimuli through direct hormone binding. This is the most specific and accurate biological process term for BRI1's core function. Supporting Evidence: PMID:9298904 A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction |
| GO:0046982 protein heterodimerization activity | IPI PMID:15548744 Heterodimerization and endocytosis of Arabidopsis brassinost... | ACCEPT | Summary: This study demonstrates heterodimerization between BRI1 and BAK1/AtSERK3, which is essential for receptor activation and signaling. Reason: Experimental evidence shows BRI1 forms heterodimers with co-receptors like BAK1. This heterodimerization activity is crucial for brassinosteroid signaling. Supporting Evidence: PMID:15548744 Heterodimerization and endocytosis of Arabidopsis brassinosteroid receptors BRI1 and AtSERK3 (BAK1) |
| GO:0009742 brassinosteroid mediated signaling pathway | IEP PMID:9298904 A putative leucine-rich repeat receptor kinase involved in b... | ACCEPT | Summary: This is another annotation for brassinosteroid signaling pathway with IEP evidence from the original BRI1 study. BRI1 mediates BR signaling. Reason: Expression pattern evidence (IEP) from the original study supports BRI1's role in brassinosteroid signaling pathways. This is a core biological process for BRI1. Supporting Evidence: PMID:9298904 A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction |
| GO:0006468 protein phosphorylation | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. |
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Download this section (compressed HTML)Q: What are the structural determinants in the island domain that confer brassinosteroid binding specificity and how do they differ between plant species?
Suggested experts: Plant hormone receptor specialists, Structural biologists working on LRR domains
Q: How does the kinase domain dual-specificity mechanism distinguish between serine/threonine and tyrosine phosphorylation targets?
Suggested experts: Protein kinase specialists, Plant signal transduction researchers
Q: What governs the temporal and spatial dynamics of BRI1 trafficking between plasma membrane and endosomal compartments?
Suggested experts: Plant cell biology researchers, Receptor trafficking specialists
Q: How does BRI1 coordinate with other receptor kinases to integrate brassinosteroid signaling with other hormonal pathways?
Suggested experts: Plant hormone crosstalk researchers, Systems biology specialists
Experiment: Use hydrogen-deuterium exchange mass spectrometry and cross-linking mass spectrometry to map conformational changes in the island domain before and after brassinolide binding. Generate island domain deletion/substitution mutants and test co-receptor interaction using co-immunoprecipitation and proximity ligation assays.
Hypothesis: The island domain undergoes conformational changes upon brassinosteroid binding that are essential for co-receptor recruitment
Experiment: Perform quantitative phosphoproteomics on BRI1 complexes with different co-receptors (BAK1, SERK1, TTL) using stable isotope labeling. Use kinase assays with recombinant proteins to map substrate specificity changes in different receptor complexes.
Hypothesis: BRI1 dual-specificity kinase activity is regulated by differential co-receptor binding and creates distinct phosphorylation signatures
Experiment: Generate phosphomimetic and phosphodeficient mutants of BRI1 cytoplasmic domain residues and analyze receptor trafficking using live-cell imaging with fluorescently-tagged BRI1. Combine with proximity biotinylation to identify trafficking machinery components.
Hypothesis: BRI1 endosomal trafficking is required for sustained signaling and involves specific phosphorylation-dependent internalization signals
Experiment: Use cyclic nucleotide biosensors and cGMP measurements to test guanylyl cyclase activity in BRI1 complexes. Generate putative cyclase domain mutants and test their ability to rescue brassinosteroid responses in bri1 mutants using complementation analysis and early response gene expression.
Hypothesis: BRI1 guanylyl cyclase activity contributes to rapid brassinosteroid responses independent of the canonical phosphorylation cascade
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