BZR1 (BRASSINAZOLE-RESISTANT 1) is the master transcription factor of the brassinosteroid (BR) signaling pathway in Arabidopsis. It is a plant-specific, atypical bHLH-like protein of the BZR/BES1 family that binds DNA through a non-canonical N-terminal domain, recognizing the BR-response element (BRRE, CGTG(T/C)G) and E-box/G-box (CACGTG) motifs in target-gene promoters. BZR1 functions as a homodimer and regulates thousands of BR-responsive genes, acting predominantly as a transcriptional repressor (notably of feedback-regulated BR biosynthetic genes such as CPD and DWF4) but also as an activator on other promoters. The activity, stability, and nucleocytoplasmic distribution of BZR1 are controlled by phosphorylation. The GSK3-like kinase BIN2 phosphorylates BZR1 to promote its nuclear export, cytoplasmic retention (via 14-3-3 binding) and degradation, whereas BR signaling activates the PP2A/BSU1 phosphatases that dephosphorylate BZR1, allowing it to accumulate in the nucleus and bind DNA. Dephosphorylated, nuclear BZR1 drives BR-induced cell elongation and growth while also mediating negative feedback on BR biosynthesis. Through interaction with other transcription factors (e.g. PIF4, DELLAs, TCPs) BZR1 integrates BR signaling with light, temperature, and gibberellin pathways, and it contributes to developmental processes including hypocotyl elongation, ovule and seed development, and female germline specification.
Definition: A DNA-binding transcription factor activity, dependent on dephosphorylation downstream of brassinosteroid signaling, that regulates transcription of brassinosteroid-responsive genes through binding to the brassinosteroid-response element (BRRE, CGTG(T/C)G).
Justification: BZR1/BES1-family factors define a plant-specific, phosphorylation-gated class of TFs that bind the BRRE element; no existing MF term captures BRRE-element specificity.
Parent term: DNA-binding transcription factor activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | ACCEPT | Summary: BZR1 is a sequence-specific DNA-binding transcription factor of the BZR/BES1 family that recognizes the BRRE and E-box/G-box motifs. This InterPro-based electronic annotation captures the core molecular function and is corroborated by direct experimental evidence. Reason: Core molecular function, supported by IEA (InterPro IPR033264) and independently by IDA (PMID:21074725) and biochemical work (PMID:15681342). Supporting Evidence: PMID:15681342 BZR1 is a transcriptional repressor that has a previously unknown DNA binding domain and binds directly to the promoters of feedback-regulated BR biosynthetic genes. file:ARATH/BZR1/BZR1-deep-research-falcon.md It binds BRRE/E-box-associated promoters and can activate or repress BR-responsive genes controlling growth and BR homeostasis |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: BZR1 acts in the nucleus, where dephosphorylated BZR1 accumulates to bind target promoters. Nuclear localization is the functional compartment and is well-supported experimentally. Reason: Core localization; consistent with UniProt subcellular location (Nucleus) and experimental IDA evidence. Supporting Evidence: PMID:11970900 BZR1 protein accumulates in the nucleus of elongating cells of dark-grown hypocotyls and is stabilized by BR signaling and the bzr1-1D mutation. file:ARATH/BZR1/BZR1-deep-research-falcon.md phosphorylated forms are biased toward cytoplasmic sequestration, while dephosphorylated forms accumulate in the nucleus and drive transcriptional outputs |
| GO:0006351 DNA-templated transcription | IEA GO_REF:0000002 | MODIFY | Summary: This generic process term (DNA-templated transcription) is the act of transcription itself rather than the regulatory role of BZR1. BZR1 is a sequence-specific regulatory transcription factor, not a component of the basal transcription machinery; the more accurate process is regulation of transcription. Reason: BZR1 regulates transcription of target genes (acting as repressor/activator) rather than carrying out the transcription reaction. Replace with regulation of DNA-templated transcription. Proposed replacements: regulation of DNA-templated transcription Supporting Evidence: PMID:21074725 There are 450 BRBT genes activated, 462 repressed, and 41 affected in complex ways by BR, indicating BZR1 can be activator and repressor for different genes. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000117 | ACCEPT | Summary: BZR1 regulates transcription of thousands of BR-responsive target genes, acting as both repressor and activator. This ARBA electronic annotation correctly captures the regulatory process. Reason: Accurate, well-supported process term for a transcriptional regulator. Supporting Evidence: PMID:21074725 There are 450 BRBT genes activated, 462 repressed, and 41 affected in complex ways by BR, indicating BZR1 can be activator and repressor for different genes. file:ARATH/BZR1/BZR1-deep-research-falcon.md It regulates BR-responsive gene expression (activation and repression depending on partners/context), thereby controlling growth programs and BR homeostasis |
| GO:0009742 brassinosteroid mediated signaling pathway | IEA GO_REF:0000002 | ACCEPT | Summary: BZR1 is the master nuclear effector of the BR signaling pathway, transducing the dephosphorylation signal into BR-responsive gene expression. This is a core process for BZR1. Reason: Core biological process; matches strong experimental evidence (also annotated IMP from PMID:11970900). Supporting Evidence: PMID:11970900 BZR1 is a positive regulator of the BR signaling pathway that mediates both downstream BR responses and feedback regulation of BR biosynthesis. file:ARATH/BZR1/BZR1-deep-research-falcon.md acts as a principal nuclear effector of the BR receptor-initiated signaling cascade |
| GO:0005515 protein binding | IPI PMID:17681130 An essential role for 14-3-3 proteins in brassinosteroid sig... | REMOVE | Summary: This IPI annotation records interaction of BZR1 with 14-3-3 (GRF6) and a GSK3-like kinase (ASK7), regulators of BZR1 stability/localization. The generic protein binding term is uninformative about molecular function. Reason: GO:0005515 protein binding is non-informative and should be replaced by informative MF terms (DNA binding, repressor activity, TF binding, dimerization) captured elsewhere in this review. The 14-3-3 interaction itself is a regulatory PTM readout, not a defining molecular function of BZR1. Supporting Evidence: PMID:17873094 GSK3-like kinases induce the nuclear export of BZR1 by modulating BZR1 interaction with the 14-3-3 proteins. |
| GO:0005515 protein binding | IPI PMID:22307275 Brassinosteroid regulates stomatal development by GSK3-media... | REMOVE | Summary: Interaction with the GSK3-like kinase BIN2 (ASK7) in the context of BR regulation of stomatal development. Generic protein binding term is uninformative. Reason: Non-informative MF term. The BIN2-BZR1 relationship is a kinase-substrate regulatory interaction, not a core molecular function descriptor. Supporting Evidence: PMID:17873094 GSK3-like kinases induce the nuclear export of BZR1 by modulating BZR1 interaction with the 14-3-3 proteins. |
| GO:0005515 protein binding | IPI PMID:22820377 Brassinosteroid, gibberellin and phytochrome impinge on a co... | REMOVE | Summary: Records interactions of BZR1 with DELLA proteins (RGL1, GAI, RGA) in a common BR/GA/phytochrome transcription module. Generic protein binding term is uninformative. Reason: Non-informative MF term. The biologically meaningful aspect (integration with GA signaling via DELLA/TF interactions) is better captured by DNA-binding transcription factor binding (proposed as a NEW term) and the BR signaling process term. Supporting Evidence: PMID:22820377 DELLAs directly interacted with BZR1 and inhibited BZR1-DNA binding both in vitro and in vivo. |
| GO:0005515 protein binding | IPI PMID:22820378 Interaction between BZR1 and PIF4 integrates brassinosteroid... | REMOVE | Summary: Records the well-characterized BZR1-PIF4 (and PIF1) interaction that integrates BR with light/temperature signaling; the two TFs co-bind ~2000 common targets. Although biologically important, the generic protein binding term is uninformative. Reason: Non-informative MF term. The informative molecular function is BZR1 binding a DNA-binding transcription factor (PIF4); proposed as a NEW GO:0140297 annotation. Supporting Evidence: PMID:22820378 BZR1 and PIF4 interact with each other in vitro and in vivo, bind to nearly 2,000 common target genes, and synergistically regulate many of these target genes. |
| GO:0005515 protein binding | IPI PMID:28650476 CrY2H-seq: a massively multiplexed assay for deep-coverage i... | REMOVE | Summary: High-throughput CrY2H-seq interactome data recording BZR1 interactions with several transcription factors (DELLAs, TCP15/21, TCP13). Generic protein binding term is uninformative. Reason: Non-informative MF term from a large-scale interactome screen; informative partner-class function (TF binding) captured by proposed GO:0140297. Supporting Evidence: PMID:28650476 CrY2H-seq: a massively multiplexed assay for deep-coverage interactome mapping. |
| GO:0005515 protein binding | IPI PMID:32612234 Extensive signal integration by the phytohormone protein net... | REMOVE | Summary: Large-scale phytohormone protein-protein interaction network recording many BZR1 partners, including numerous TCP transcription factors and DELLAs. Generic protein binding term is uninformative. Reason: Non-informative MF term from a high-throughput network; informative function (binding DNA-binding TFs) captured by proposed GO:0140297. Supporting Evidence: PMID:32612234 Extensive signal integration by the phytohormone protein network. |
| GO:0005515 protein binding | IPI PMID:37335918 Plant-specific BLISTER interacts with kinase BIN2 and BRASSI... | REMOVE | Summary: Records interaction of BZR1 with the plant-specific BLISTER (BLI) protein, which cooperates with BZR1 to activate BR-responsive genes during skotomorphogenesis. Generic protein binding term is uninformative. Reason: Non-informative MF term. The cooperative transcriptional activation function is better represented by BZR1's DNA-binding/TF activity terms. Supporting Evidence: PMID:37335918 BLI cooperates with the BRASSINAZOLE RESISTANT1 (BZR1) transcription factor to facilitate the transcriptional activation of BR-responsive genes. |
| GO:0000987 cis-regulatory region sequence-specific DNA binding | IPI PMID:36748257 Signaling by the EPFL-ERECTA family coordinates female germl... | ACCEPT | Summary: BZR1 directly binds the cis-regulatory region (promoter) of NSN1 to activate its expression during female germline specification, demonstrating sequence-specific cis-regulatory DNA binding. This is an informative molecular function consistent with BZR1's role as a sequence-specific TF binding BRRE/E-box motifs. Reason: Informative, experimentally supported MF term for a sequence-specific DNA-binding TF. The binding/activation of the NSN1 promoter is direct. Supporting Evidence: PMID:36748257 BZR1 coordinates female germline specification by directly activating the expression of a nucleolar GTP-binding protein, NUCLEOSTEMIN-LIKE 1 (NSN1). |
| GO:0009414 response to water deprivation | IMP PMID:36508461 A role for brassinosteroid signalling in decision-making pro... | KEEP AS NON CORE | Summary: This annotation derives from a forward-genetic screen combining light and water withdrawal that identified BR-pathway (primarily BIN2) decision-making mutants. BZR1 acts downstream within the BR pathway; a role in differential growth under water deprivation is a peripheral, pathway-level developmental output rather than a core BZR1 function. Reason: Peripheral physiological/developmental output of BR signaling; the screen centered on BIN2 alleles, with BZR1 acting within the same pathway. Retain as non-core context. Supporting Evidence: PMID:36508461 This identified BRASSINOSTEROID INSENSITIVE 2 (BIN2) alleles as decision mutants with "confused" phenotypes. |
| GO:0009416 response to light stimulus | IMP PMID:36508461 A role for brassinosteroid signalling in decision-making pro... | KEEP AS NON CORE | Summary: BZR1 contributes to light-modulated differential growth (photomorphogenesis, hypocotyl-versus-root decisions) within the BR pathway, integrating with light signaling (e.g. via PIF4 and HY5 target overlap). This is a peripheral developmental output rather than a core molecular function. Reason: BR/BZR1 crosstalk with light signaling is well-documented, but light response is a downstream pathway output; retain as non-core. Supporting Evidence: PMID:21074725 These results demonstrate that phytochrome and BR pathways antagonistically regulate seedling photomorphogenesis largely by regulating common downstream genes. |
| GO:0005634 nucleus | ISM GO_REF:0000122 | ACCEPT | Summary: Computational (AtSubP) prediction of nuclear localization, consistent with the functional nuclear localization of BZR1 established experimentally. Reason: Correct core localization; redundant with experimental IDA nucleus annotation but acceptable. Supporting Evidence: PMID:11970900 BZR1 protein accumulates in the nucleus of elongating cells of dark-grown hypocotyls and is stabilized by BR signaling and the bzr1-1D mutation. |
| GO:0005515 protein binding | IPI PMID:21258370 PP2A activates brassinosteroid-responsive gene expression an... | REMOVE | Summary: Records interaction of BZR1 with PP2A B' regulatory subunits, which dephosphorylate and thereby activate BZR1. Generic protein binding term is uninformative about molecular function. Reason: Non-informative MF term. The PP2A-BZR1 interaction is a phosphatase-substrate regulatory event, not a defining molecular function of BZR1. Supporting Evidence: PMID:17873094 BR-activated phosphatase mediates rapid nuclear localization of BZR1. |
| GO:0005515 protein binding | IPI PMID:25663622 Formation and dissociation of the BSS1 protein complex regul... | REMOVE | Summary: Records interaction of BZR1 with the BSS1/BOP1 complex, which sequesters BZR1 and regulates BR signaling. Generic protein binding term is uninformative. Reason: Non-informative MF term; regulatory sequestration interaction, not a core molecular function descriptor. Supporting Evidence: PMID:25663622 Formation and dissociation of the BSS1 protein complex regulates plant development via brassinosteroid signaling. |
| GO:0003700 DNA-binding transcription factor activity | IDA PMID:21074725 Integration of brassinosteroid signal transduction with the ... | ACCEPT | Summary: Direct experimental demonstration (genome-wide ChIP-chip plus binding assays) that BZR1 is a sequence-specific DNA-binding transcription factor regulating hundreds of BR-responsive target genes via BRRE and E-box/G-box motifs. This is the core molecular function. Reason: Strong IDA support for the core MF; BZR1 binds DNA and regulates transcription of target genes. Supporting Evidence: PMID:21074725 BZR1 binds to the BR-response element (BRRE, CGTGT/CG) of BR-repressed genes. |
| GO:0048316 seed development | IMP PMID:22914576 BR signal influences Arabidopsis ovule and seed number throu... | KEEP AS NON CORE | Summary: BR signaling through BZR1 influences seed number; dephospho-BZR1 level correlates with ovule and seed number, and BZR1 regulates ovule-development genes. This is a downstream developmental output of BZR1's transcriptional activity. Reason: Developmental output (one of many BR-regulated processes), not the core molecular/biological function; retain as non-core. Supporting Evidence: PMID:22914576 the dephosphorylation level of BZR1 is consistent with ovule and seed number. |
| GO:0048481 plant ovule development | IMP PMID:22914576 BR signal influences Arabidopsis ovule and seed number throu... | KEEP AS NON CORE | Summary: BZR1 modulates ovule initiation and development by regulating expression of ovule-development genes (HLL, ANT, AP2), acting antagonistically with AP2. A downstream developmental output of BZR1. Reason: Developmental output of BR/BZR1 transcriptional control; retain as non-core. Supporting Evidence: PMID:22914576 BR regulates the expression level of genes related to ovule development, including HLL, ANT, and AP2, either directly by targeting the promoter sequences or indirectly via regulation by BR-induced transcription factor BZR1. |
| GO:0045892 negative regulation of DNA-templated transcription | IDA PMID:15681342 BZR1 is a transcriptional repressor with dual roles in brass... | ACCEPT | Summary: BZR1 is a transcriptional repressor that binds directly to promoters (BRRE) of feedback-regulated BR biosynthetic genes and represses their expression. This is a core, experimentally demonstrated function. Reason: Core repressor activity directly demonstrated; defining feature of BZR1 (cf. activator BES1). Supporting Evidence: PMID:15681342 Here we show that BZR1 is a transcriptional repressor that has a previously unknown DNA binding domain and binds directly to the promoters of feedback-regulated BR biosynthetic genes. |
| GO:0006355 regulation of DNA-templated transcription | TAS PMID:11970900 Nuclear-localized BZR1 mediates brassinosteroid-induced grow... | ACCEPT | Summary: BZR1 is a transcriptional regulator within the BR pathway. TAS annotation of the general regulation-of-transcription process is accurate, though less specific than the negative-regulation annotation also present. Reason: Accurate process term, consistent with BZR1's role as a sequence-specific transcriptional regulator. Supporting Evidence: PMID:11970900 Nuclear-localized BZR1 mediates brassinosteroid-induced growth and feedback suppression of brassinosteroid biosynthesis. |
| GO:0005829 cytosol | IDA PMID:17873094 Nucleocytoplasmic shuttling of BZR1 mediated by phosphorylat... | KEEP AS NON CORE | Summary: BZR1 is a nucleocytoplasmic shuttling protein; phosphorylated BZR1 is exported and retained in the cytosol (via 14-3-3 binding). The cytosolic localization is real and experimentally observed, but it represents the inactive/exported pool rather than the compartment where BZR1 performs its transcriptional function. Reason: Genuine experimental localization, but cytosol corresponds to the inactive sequestered form; nucleus is the functional compartment. Retain as non-core. Supporting Evidence: PMID:17873094 We show here that BZR1 functions as a nucleocytoplasmic shuttling protein and GSK3-like kinases induce the nuclear export of BZR1 by modulating BZR1 interaction with the 14-3-3 proteins. file:ARATH/BZR1/BZR1-deep-research-falcon.md BIN2-phosphorylated BZR1 is retained more in the cytoplasm through 14-3-3 association, whereas dephosphorylated BZR1 accumulates in the nucleus to regulate transcription |
| GO:0003677 DNA binding | IDA PMID:15681342 BZR1 is a transcriptional repressor with dual roles in brass... | MODIFY | Summary: BZR1 binds DNA directly through its N-terminal domain, recognizing the BRRE element. The generic DNA binding term is correct but less informative than sequence-specific terms; BZR1 binds a defined cis-regulatory motif. Reason: BZR1 binds DNA in a sequence-specific manner at cis-regulatory regions (BRRE); replace bare DNA binding with the more informative sequence-specific cis-regulatory region binding term. Proposed replacements: transcription cis-regulatory region binding Supporting Evidence: PMID:15681342 BZR1 is a transcriptional repressor that has a previously unknown DNA binding domain and binds directly to the promoters of feedback-regulated BR biosynthetic genes. PMID:21074725 BZR1 binds to the BR-response element (BRRE, CGTGT/CG) of BR-repressed genes. |
| GO:0005634 nucleus | IDA PMID:11970900 Nuclear-localized BZR1 mediates brassinosteroid-induced grow... | ACCEPT | Summary: Direct experimental evidence that BZR1 localizes to the nucleus, where it accumulates in elongating hypocotyl cells and is stabilized by BR signaling. The nucleus is the functional compartment for BZR1's transcriptional activity. Reason: Core localization with strong IDA support. Supporting Evidence: PMID:11970900 BZR1 protein accumulates in the nucleus of elongating cells of dark-grown hypocotyls and is stabilized by BR signaling and the bzr1-1D mutation. |
| GO:0009742 brassinosteroid mediated signaling pathway | IMP PMID:11970900 Nuclear-localized BZR1 mediates brassinosteroid-induced grow... | ACCEPT | Summary: Genetic evidence (dominant bzr1-1D suppresses BR-deficient and bri1 phenotypes) establishes BZR1 as the key nuclear effector mediating BR-induced growth and feedback regulation of BR biosynthesis. Core biological process. Reason: Core process, strongly supported by mutant phenotype analysis (IMP). Supporting Evidence: PMID:11970900 A dominant mutation bzr1-1D suppresses BR-deficient and BR-insensitive (bri1) phenotypes and enhances feedback inhibition of BR biosynthesis. |
| GO:0001227 DNA-binding transcription repressor activity, RNA polymerase II-specific | IDA PMID:15681342 BZR1 is a transcriptional repressor with dual roles in brass... | NEW | Summary: NEW annotation. BZR1 functions as a sequence-specific DNA-binding transcriptional repressor, binding the BRRE element in promoters of BR biosynthetic genes to repress their transcription. This informative molecular-function term captures the repressor activity that the generic DNA-binding TF activity and the process-level negative-regulation terms do not fully specify. Reason: BZR1's defining biochemical activity is sequence-specific transcriptional repression (distinguishing it from the activator paralog BES1); directly demonstrated by promoter binding and repression of BR biosynthetic genes. Supporting Evidence: PMID:15681342 Here we show that BZR1 is a transcriptional repressor that has a previously unknown DNA binding domain and binds directly to the promoters of feedback-regulated BR biosynthetic genes. PMID:21074725 BZR1 binds to the BR-response element (BRRE, CGTGT/CG) of BR-repressed genes. |
| GO:0140297 DNA-binding transcription factor binding | IPI PMID:22820378 Interaction between BZR1 and PIF4 integrates brassinosteroid... | NEW | Summary: NEW annotation. BZR1 physically interacts with DNA-binding transcription factors (notably PIF4 and PIF1) to integrate BR with light/temperature signaling; BZR1-PIF4 co-bind ~2000 common targets and synergistically regulate them. BZR1 also binds other TFs (TCPs). This informative MF term replaces the generic protein-binding annotations for its TF partners. Reason: A defining mode of BZR1 action is heterotypic interaction with other DNA-binding TFs to co-regulate shared targets; informative replacement for several removed GO:0005515 annotations. Supporting Evidence: PMID:22820378 BZR1 and PIF4 interact with each other in vitro and in vivo, bind to nearly 2,000 common target genes, and synergistically regulate many of these target genes. file:ARATH/BZR1/BZR1-deep-research-falcon.md emphasize BZR1 as an integration node for light, auxin, GA, ethylene, and stress signaling |
| GO:0042803 protein homodimerization activity | IDA PMID:30287951 Structural basis for brassinosteroid response by BIL1/BZR1. | NEW | Summary: NEW annotation. The crystal structure of the BIL1/BZR1 DNA-binding domain (residues 21-104) in complex with DNA shows that BZR1 binds its target element as a homodimer, and UniProt curates BZR1 as a homodimer. Homodimerization is integral to sequence-specific DNA recognition. Reason: Structurally demonstrated homodimerization that underlies DNA binding; an informative molecular function not otherwise represented. PMID:30287951 is the X-ray structure paper cited in UniProt; evidence is taken from the UniProt record as the full text was not in cached publications. Supporting Evidence: PMID:30287951 Here, we show the non-canonical bHLH dimer formation of BIL1/BZR1 to optimize the interaction network with DNA and the orientation of a key residue for NN-BRRE-core motif recognition. |
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Q: Is the cytosolic pool of BZR1 entirely the phosphorylated/inactive form, or does cytosolic BZR1 have any signaling role beyond being a shuttling intermediate?
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