PISTILLATA (PI) is a B-class floral homeotic MADS-box (MIKC-type) transcription factor of Arabidopsis thaliana that specifies petal (whorl 2) and stamen (whorl 3) identity within the ABC model of flower development. PI functions as an obligate heterodimer with APETALA3 (AP3); the AP3/PI heterodimer binds CArG-box DNA motifs in the cis-regulatory regions of target genes through its MADS domain and acts within higher-order floral quartet complexes together with SEPALLATA (SEP) and APETALA1/AGAMOUS proteins to regulate RNA polymerase II transcription. The protein has the canonical MIKC architecture: an N-terminal MADS domain (DNA binding and dimerization), an intervening I region, a K-box (coiled-coil region governing dimerization specificity), and a C-terminal domain. Nuclear import of PI requires co-expression with AP3, so heterodimer formation couples partner availability to nuclear accumulation and transcriptional activity. Loss of PI function transforms petals into sepals and stamens into carpels. AP3/PI both autoregulates the AP3 and PI genes and directly regulates downstream targets such as NAP, AP1, and the GATA factors GNC/GNL.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding | IBA GO_REF:0000033 | ACCEPT | Summary: As a MIKC MADS-box transcription factor, the AP3/PI heterodimer binds CArG-box cis-regulatory motifs in the promoters of floral target genes to regulate their RNA polymerase II transcription. This phylogenetically inferred term accurately captures PI's core sequence-specific cis-regulatory DNA binding. Reason: Sequence-specific cis-regulatory (CArG-box) DNA binding is a core molecular function of PI, supported experimentally by direct promoter binding (ChIP) and by the documented CArG-box specificity of the AP3/PI heterodimer. Supporting Evidence: PMID:16640596 the floral homeotic PISTILLATA (PI) protein, required for petal and stamen development, has the ability to bind directly to the promoter region of AP1 file:ARATH/PI/PI-notes.md Forms a heterodimer with APETALA3, capable of binding to CArG-box sequences. |
| GO:0000981 DNA-binding transcription factor activity, RNA polymerase II-specific | IBA GO_REF:0000033 | ACCEPT | Summary: PI is a sequence-specific DNA-binding transcription factor that, as the AP3/PI heterodimer, regulates RNA polymerase II transcription of floral identity genes. This RNA Pol II-specific TF activity term is the most precise molecular-function descriptor for PI and is well supported. Reason: DNA-binding transcription factor activity is the defining molecular function of PI; the RNA Pol II-specific qualifier is appropriate for a eukaryotic protein-coding gene regulator. Supporting Evidence: PMID:16640596 the floral homeotic PISTILLATA (PI) protein, required for petal and stamen development, has the ability to bind directly to the promoter region of AP1 PMID:12837945 Molecular and phylogenetic analyses of the complete MADS-box transcription factor family in Arabidopsis file:ARATH/PI/PI-deep-research-falcon.md MIKC-type MADS-domain sequence-specific DNA-binding transcription factor |
| GO:0006357 regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | ACCEPT | Summary: PI participates in RNA polymerase II transcriptional regulation of floral target genes as part of the AP3/PI heterodimer and floral quartet complexes. This process term is correct but is a general parent of the more specific floral specification process; it is retained as a valid process annotation. Reason: Regulation of RNA Pol II transcription is the mechanistic process through which PI exerts its developmental function and is well supported by direct target regulation studies. Supporting Evidence: PMID:16640596 provides independent support for the hypothesis that AP1 is a direct target of the AP3/PI heterodimer file:ARATH/PI/PI-notes.md AP3/PI both autoregulates the AP3 and PI genes and directly regulates downstream targets such as NAP, AP1, and the GATA factors GNC/GNL. |
| GO:0000977 RNA polymerase II transcription regulatory region sequence-specific DNA binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based electronic annotation for sequence-specific binding to RNA Pol II regulatory regions. This is consistent with PI's experimentally established CArG-box DNA binding as part of the AP3/PI heterodimer and overlaps the more curator-preferred IBA term GO:0000978. Reason: Accurate for a MADS-box TF; PI binds sequence-specific cis-regulatory DNA. Slightly redundant with GO:0000978 but biologically correct. Supporting Evidence: PMID:16640596 the floral homeotic PISTILLATA (PI) protein, required for petal and stamen development, has the ability to bind directly to the promoter region of AP1 |
| GO:0003677 DNA binding | IEA GO_REF:0000002 | ACCEPT | Summary: Generic DNA binding from InterPro MADS-box domain signatures. True for PI but less informative than the sequence-specific cis-regulatory binding terms (GO:0000978/GO:0000977) that are also annotated. Kept as a correct but general parent. Reason: PI binds DNA via its MADS domain; this is correct, though more specific sequence-specific DNA binding terms better capture the function. Supporting Evidence: file:ARATH/PI/PI-notes.md an N-terminal MADS domain (DNA binding and dimerization) |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based electronic annotation of DNA-binding transcription factor activity, the core molecular function of PI. Redundant with the ISS- and IBA-supported TF activity annotations but biologically correct. Reason: DNA-binding transcription factor activity is the defining molecular function of this MADS-box protein. Supporting Evidence: PMID:12837945 Molecular and phylogenetic analyses of the complete MADS-box transcription factor family in Arabidopsis |
| GO:0005634 nucleus | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic annotation of nuclear localization. PI is a transcription factor that functions in the nucleus; nuclear import requires heterodimerization with AP3. This is well supported by direct experimental evidence (IDA). Reason: Nucleus is the functional location of the active AP3/PI heterodimer and is experimentally confirmed. Supporting Evidence: PMID:8698240 coexpression of AP3-GUS with PI, or PI-GUS with AP3, resulted in nuclear localization of GUS activity |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: Generic InterPro-based annotation for regulation of DNA-templated transcription. Correct but a broad parent of the more specific RNA Pol II transcription regulation (GO:0006357) already annotated for PI. Reason: PI regulates transcription of floral target genes; the term is accurate though general. Supporting Evidence: PMID:16640596 provides independent support for the hypothesis that AP1 is a direct target of the AP3/PI heterodimer |
| GO:0010093 specification of floral organ identity | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learning electronic annotation to the core biological process of PI, specification of floral organ identity. This is the central developmental role of the B-class gene PI and is independently supported by classical genetic (IMP) evidence. Reason: Specification of petal and stamen identity is the defining biological process of PI; the electronic call agrees with strong experimental evidence. Supporting Evidence: file:ARATH/PI/PI-notes.md Mutations in PI cause transformation of petals into sepals and stamina into carpels. |
| GO:0045944 positive regulation of transcription by RNA polymerase II | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro-based electronic annotation asserting positive (activating) regulation of RNA Pol II transcription. PI/AP3 does activate some targets (e.g. NAP), but it also directly represses others (AP1, GNC/GNL), so PI is a context- dependent dual regulator rather than a dedicated activator. The directional term over-specifies one mode of action. Reason: PI acts as both an activator and a repressor of RNA Pol II targets; the activator-only directional term is not generally accurate and over-states a single regulatory direction inferred electronically from domain signatures. Supporting Evidence: PMID:16640596 AP3/PI directly acts, in combination with other factors, to restrict the expression of AP1 file:ARATH/PI/PI-notes.md AP3/PI represses GATA21/GNC and GATA22/GNL. |
| GO:0046983 protein dimerization activity | IEA GO_REF:0000002 | ACCEPT | Summary: Protein dimerization activity is a core molecular function of PI. PI functions as an obligate heterodimer with AP3; heterodimer formation (via the MADS and K domains) is required for DNA binding, nuclear import, and all known PI activity. This is one of the most central and well-supported functions of PI. Reason: AP3/PI obligate heterodimerization is essential for PI function; dimerization is therefore a core molecular function, consistent with project guidance to retain PI/AP3 heterodimerization as core. Supporting Evidence: PMID:15604664 the MADS domain that mediates DNA binding and dimerization, and the K domain that mediates protein protein interaction file:ARATH/PI/PI-notes.md Forms a heterodimer with APETALA3, capable of binding to CArG-box sequences. file:ARATH/PI/PI-deep-research-falcon.md Class B proteins AP3 and PI bind DNA only as a heterodimer; AP3-PI is the core B-class functional unit required for autoregulatory maintenance. |
| GO:0005515 protein binding | IPI PMID:15604664 Defining subdomains of the K domain important for protein-pr... | MARK AS OVER ANNOTATED | Summary: Generic protein binding from an IPI interaction with SEP3 (UniProtKB O22456) via the K domain. The underlying biology (PI participating in protein-protein interactions / heterodimer and floral-quartet complex formation) is real and important, but the generic protein binding term is uninformative; the specific function is better captured by protein dimerization activity (GO:0046983). Reason: Bare protein binding (GO:0005515) provides no functional specificity; per curation guidelines a more informative term is preferred, and PI's dimerization function is already represented by GO:0046983. Supporting Evidence: PMID:15604664 the K domain that mediates protein protein interaction |
| GO:0000976 transcription cis-regulatory region binding | IPI PMID:25533953 An Arabidopsis gene regulatory network for secondary cell wa... | KEEP AS NON CORE | Summary: This IPI annotation derives from a large-scale yeast-one-hybrid (Y1H) secondary cell wall gene regulatory network screen, in which PI scored as binding the promoter of the xylan-biosynthesis gene IRX14 (AT4G36890). The molecular activity (binding cis-regulatory DNA) is genuinely true for a MADS-box TF such as PI. However, the supporting evidence is a high-throughput Y1H hit in a root/xylem context where PI is not normally expressed (each promoter bound an average of 38 TFs), so it most likely reflects in vitro DNA-binding capacity rather than an in vivo floral regulatory function. The general cis-regulatory binding term is retained but flagged as non-core; PI's physiologically relevant DNA binding is the CArG-box binding of the AP3/PI heterodimer at floral targets. Reason: The MF term is correct for a MADS TF, but the single supporting datum is a high-throughput Y1H interaction with a secondary-cell-wall promoter outside PI's normal expression domain and is not part of PI's core floral function. Per guidelines an experimental annotation is not removed; it is retained as non-core. Supporting Evidence: PMID:25533953 Each promoter interacted with an average of 38 different proteins, generating even more possibilities for combinatorial, redundant, or condition-specific gene regulation. file:ARATH/PI/PI-notes.md PI is a floral organ-identity TF not normally expressed in root xylem; this Y1H hit is best treated as a non-core/over-annotated interaction |
| GO:0005634 nucleus | ISM GO_REF:0000122 | ACCEPT | Summary: Sequence-model (AtSubP) prediction of nuclear localization, consistent with PI's function as a transcription factor and with direct experimental evidence that the AP3/PI heterodimer localizes to the nucleus. Reason: Nuclear localization of the active heterodimer is experimentally confirmed and is the functional compartment for PI. Supporting Evidence: PMID:8698240 coexpression of AP3-GUS with PI, or PI-GUS with AP3, resulted in nuclear localization of GUS activity |
| GO:0010093 specification of floral organ identity | IMP PMID:2535466 Genes directing flower development in Arabidopsis. | ACCEPT | Summary: Classical genetic (IMP) annotation to PI's core biological process. Loss-of-function pi mutants transform petals into sepals and stamens into carpels, the defining homeotic phenotype establishing PI as a B-class organ identity gene. This is the central, best-supported function of PI. Reason: Specification of petal and stamen identity is the core developmental role of PI, established by mutant phenotype analysis. Supporting Evidence: file:ARATH/PI/PI-notes.md Mutations in PI cause transformation of petals into sepals and stamina into carpels. file:ARATH/PI/PI-deep-research-falcon.md B-class activity is required for petal and stamen identity in Arabidopsis. |
| GO:0003677 DNA binding | IDA PMID:16640596 Direct regulation of the floral homeotic APETALA1 gene by AP... | ACCEPT | Summary: Direct experimental (IDA) demonstration that PI binds DNA, shown by chromatin immunoprecipitation of PI at the AP1 promoter. This is direct evidence for PI's core DNA-binding activity in vivo (as the AP3/PI heterodimer). Reason: In vivo DNA binding by PI is directly demonstrated by ChIP; DNA binding is a core molecular function. More specific sequence-specific terms also apply but this general term is correct and experimentally grounded. Supporting Evidence: PMID:16640596 the floral homeotic PISTILLATA (PI) protein, required for petal and stamen development, has the ability to bind directly to the promoter region of AP1 |
| GO:0003700 DNA-binding transcription factor activity | ISS PMID:12837945 Molecular and phylogenetic analyses of the complete MADS-box... | ACCEPT | Summary: Sequence-similarity (ISS) annotation assigning DNA-binding transcription factor activity based on the MADS-box family analysis. This is PI's core molecular function and is independently supported by experimental DNA binding and transcriptional regulation data. Reason: DNA-binding transcription factor activity is the defining function of this MADS-box protein and is experimentally corroborated. Supporting Evidence: PMID:12837945 Molecular and phylogenetic analyses of the complete MADS-box transcription factor family in Arabidopsis |
| GO:0003700 DNA-binding transcription factor activity | ISS PMID:11118137 Arabidopsis transcription factors: genome-wide comparative a... | ACCEPT | Summary: Sequence-similarity (ISS) annotation of DNA-binding transcription factor activity from a genome-wide TF comparative analysis. Redundant with the other TF-activity annotations but biologically correct for this MADS-box protein. Reason: DNA-binding transcription factor activity is PI's core molecular function; this ISS call is consistent with experimental evidence. Supporting Evidence: PMID:11118137 Arabidopsis transcription factors: genome-wide comparative analysis among eukaryotes |
| GO:0005634 nucleus | IDA PMID:8698240 Nuclear localization of the Arabidopsis APETALA3 and PISTILL... | ACCEPT | Summary: Direct experimental (IDA) evidence that PI localizes to the nucleus when co-expressed with AP3. Nuclear localization of the AP3/PI heterodimer is the functionally relevant compartment where PI acts as a transcription factor. Reason: Nucleus is the active site of PI function; nuclear import of the AP3/PI heterodimer is directly demonstrated. Supporting Evidence: PMID:8698240 coexpression of AP3-GUS with PI, or PI-GUS with AP3, resulted in nuclear localization of GUS activity file:ARATH/PI/PI-deep-research-falcon.md nuclear localization depends on simultaneous expression with AP3 |
| GO:0005737 cytoplasm | IDA PMID:8698240 Nuclear localization of the Arabidopsis APETALA3 and PISTILL... | KEEP AS NON CORE | Summary: Direct experimental (IDA) evidence that PI expressed alone (as a PI-GUS fusion, without AP3) is retained in the cytoplasm. This cytoplasmic localization reflects the inactive PI monomer that has not heterodimerized with AP3; upon AP3 co-expression PI relocates to the nucleus. The cytoplasmic pool is real but represents the non-functional, pre-import state rather than PI's site of action. Reason: Cytoplasmic localization is genuine (directly observed for the PI monomer) but is the inactive state; the functional/core location of PI is the nucleus, so cytoplasm is retained as a non-core localization. Supporting Evidence: PMID:8698240 Transient transformation assays of either the AP3-GUS or PI-GUS fusion protein alone resulted in cytoplasmic localization of GUS activity |
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