Maize VIVIPAROUS-1 (VP1; UniProt P26307) is a seed-specific B3-domain transcriptional regulator and the maize ortholog of Arabidopsis ABI3. It is genetically essential for coordinating the seed maturation program (acquisition of desiccation tolerance and dormancy) and for implementing ABA-responsive transcription during embryogenesis (deep-research falcon report; Suzuki et al. 2001, Pla et al. 1991, White 1995). VP1 is a modular transcription factor: it acts as (i) an ABA-dependent co-activator of seed ABA-regulated maturation genes via G-box/ABRE-related cis-elements (e.g. Em, rab28), (ii) a direct, B3-dependent sequence-specific DNA-binding activator of certain promoters (the maize anthocyanin regulator C1 via the Sph element), and (iii) a repressor of germination-associated programs in aleurone (e.g. alpha-amylase), with the co-activation and repression functions largely B3-independent and mediated by protein-protein interactions. The protein contains four conserved domains (A1, B1, B2 and the C-terminal B3 DNA-binding domain spanning residues 517-619) and an N-terminal acidic/disordered transcriptional-activation region. Loss-of-function vp1 mutants are ABA-insensitive and viviparous - they undergo precocious germination on the ear, fail to acquire desiccation tolerance, and lose normal accumulation of LEA/maturation transcripts; maize VP1 expressed in Arabidopsis abi3-6 restores green-seed/desiccation phenotypes and ABA sensitivity, demonstrating functional conservation with ABI3. A central nuance for GO annotation is that VP1 is a downstream transcriptional EFFECTOR that mediates and potentiates ABA responses (it sits at the terminal ABI3 node of the PYL-ABI1-SnRK2-ABI3 module), rather than being a component of the core PYR/PYL-PP2C-SnRK2 perception-to-transduction cascade (GO:0009738). VP1 function is nuclear (consistent with its DNA-binding transcriptional regulator role), though no direct experimental subcellular-localization assay for the maize protein was found in the retrieved literature; UniProt also lists a cytoplasmic location.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
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GO:0003677
DNA binding
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: IEA annotation from InterPro (IPR003340, B3 DNA-binding domain). VP1 contains a C-terminal B3 DNA-binding domain (residues 517-619) and binds DNA directly - it activates the maize C1 promoter via B3 binding to the Sph element.
Reason: Correct and core. The UniProt feature table annotates a TF-B3 DNA-binding domain at 517-619, and the deep-research synthesis confirms that VP1/ABI3 proteins contain four conserved domains in which B3 is the DNA-binding domain, with direct B3-dependent binding to the C1 promoter Sph element. "DNA binding" is generic but not incorrect; the more informative sequence-specific DNA-binding transcription factor activity is captured by GO:0003700 (modified below). Note that the founding study (McCarty et al. 1991) localized VP1's transactivation activity to an acidic domain and proposed that VP1 "may bind to DNA indirectly" for several targets (UniProt FUNCTION), so generic DNA binding rather than direct sequence-specific binding is the safe MF claim for the bulk of VP1 targets; direct B3-mediated binding is documented specifically for C1/Sph.
Supporting Evidence:
file:MAIZE/VP1/VP1-deep-research-falcon.md
VP1/ABI3 proteins contain four prominent conserved domains, **A1, B1, B2, and B3**, where **B3 is the DNA-binding domain**
file:MAIZE/VP1/VP1-deep-research-falcon.md
**maize *C1*** activation via B3 binding to the **Sph element**
PMID:1889090
An acidic transcriptional activation sequence was identified by fusion to the GAL4 DNA-binding domain.
|
|
GO:0003700
DNA-binding transcription factor activity
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: IEA annotation from InterPro (IPR044800, LEC2-like B3 family) for sequence-specific DNA-binding transcription factor activity. This is VP1's core molecular function - it is a transcriptional regulator that activates and represses plant nuclear (RNA Pol II) protein-coding genes. The generic term is correct but can be made more precise.
Reason: VP1 is unambiguously a sequence-specific DNA-binding transcription factor: it acts as a direct transcriptional activator of certain promoters via B3 DNA binding (C1 via the Sph element), as an ABA-dependent co-activator of seed maturation genes via G-box/ABRE elements, and as a repressor of germination genes. UniProt's original description (Cell 1991) is "a novel transcriptional activator." Because VP1 regulates RNA polymerase II protein-coding genes, the generic GO:0003700 is better represented by the more specific child term GO:0000981 (DNA-binding transcription factor activity, RNA polymerase II-specific). The essence is correct; only the level of specificity is refined.
Proposed replacements:
DNA-binding transcription factor activity, RNA polymerase II-specific
Supporting Evidence:
PMID:1889090
Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response.
PMID:1889090
Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene.
file:MAIZE/VP1/VP1-deep-research-falcon.md
VP1 functions as a **transcriptional regulator** (not an enzyme/transport protein)
file:MAIZE/VP1/VP1-deep-research-falcon.md
**Direct transcriptional activator** of some promoters via **B3 DNA binding**, exemplified by **maize *C1*** activation via B3 binding to the **Sph element**
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: IEA annotation from the UniProt subcellular-location vocabulary. VP1 is a DNA-binding transcriptional regulator, so a nuclear location is where it carries out its function.
Reason: Consistent with VP1's molecular function. The deep-research synthesis states that the evidence base strongly supports VP1 as a DNA-binding transcriptional regulator, which generally implies nuclear function, and UniProt lists Nucleus as a subcellular location. No direct GFP/fractionation experiment for maize VP1 was found in the retrieved texts, but nuclear localization is the functionally relevant location for a transcription factor and is accepted. VP1 strongly transactivates a target promoter when expressed in maize protoplasts (McCarty et al. 1991), an activity that requires access to the nuclear transcription machinery and is consistent with nuclear function.
Supporting Evidence:
file:MAIZE/VP1/VP1-deep-research-falcon.md
The retrieved evidence base strongly supports VP1 as a **DNA-binding transcriptional regulator**, which generally implies nuclear function
PMID:1889090
Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene.
|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: IEA annotation from the UniProt subcellular-location vocabulary (UniProt lists both Cytoplasm and Nucleus). VP1 carries out its function as a transcription factor in the nucleus; the cytoplasmic assignment is not where its core activity occurs.
Reason: The UniProt record lists Cytoplasm as a subcellular location, so the annotation is retained, but it does not represent VP1's core, functionally relevant compartment. The deep-research synthesis explicitly notes that no direct experimental subcellular localization assay (GFP fusion, fractionation) for maize VP1 was found, and that the evidence supports a nucleus-consistent function. A cytoplasmic pool would at most reflect a shuttling/storage population rather than the site of VP1's transcriptional activity. Marked non-core; not removed because it is a curated UniProt location.
Supporting Evidence:
file:MAIZE/VP1/VP1-deep-research-falcon.md
**explicit experimental subcellular localization (e.g., GFP fusion microscopy, fractionation)** for maize VP1 **was not found in the obtained texts**
file:MAIZE/VP1/VP1-deep-research-falcon.md
this report does not make a definitive, experimentally sourced localization claim beyond nucleus-consistent function
|
|
GO:0006355
regulation of DNA-templated transcription
|
IEA
GO_REF:0000108 |
MODIFY |
Summary: IEA annotation inferred logically from the DNA-binding transcription factor activity MF. VP1 regulates transcription of seed maturation and germination genes - primarily as an activator of ABA-inducible maturation genes (Em, rab28, C1) and as a repressor of germination-associated genes. The generic process term can be made more specific.
Reason: VP1 is genuinely a transcriptional regulator, so the term is correct, but it is the broad parent. VP1 regulates RNA polymerase II protein-coding genes and is described primarily as a transcriptional activator that potentiates ABA-responsive maturation gene expression (it can transactivate ABRE-containing promoters synergistically with ABA and directly activates C1). The more informative child term is GO:0045944 (positive regulation of transcription by RNA polymerase II). VP1 also has a separable repressor function on germination genes (alpha-amylase), which is captured separately by the proposed negative-regulation-of-germination process term below.
Proposed replacements:
positive regulation of transcription by RNA polymerase II
Supporting Evidence:
PMID:1889090
Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene.
PMID:1837331
The results obtained with the ABA-insensitive vp1 mutant show that rab 28 transcripts do not accumulate to a significant level during embryogenesis.
file:MAIZE/VP1/VP1-deep-research-falcon.md
VP1 can **transactivate ABRE-containing promoters** synergistically with ABA
file:MAIZE/VP1/VP1-deep-research-falcon.md
Distinct VP1 domains are required for different outputs: Em/C1 activation vs α-amylase repression
|
|
GO:0009738
abscisic acid-activated signaling pathway
|
IEA
GO_REF:0000043 |
MODIFY |
Summary: SPKW (GO_REF:0000043) annotation derived from the UniProt keyword "Abscisic acid signaling pathway"; snapshot-only, removed in the current GOA release. VP1's genuine ABA role is real and central, but it is a downstream transcriptional EFFECTOR that mediates/potentiates ABA responses (the terminal ABI3 node of the PYL-ABI1-SnRK2-ABI3 module) rather than a component of the core PYR/PYL-PP2C-SnRK2 perception-to-transduction cascade that GO:0009738 denotes.
Reason: GOA's removal of the bare keyword term was partly justified but should not lose the genuine biology. GO:0009738 (abscisic acid-activated signaling pathway) denotes the ABA perception-to-transduction cascade (PYR/PYL receptors, PP2C phosphatases, SnRK2 kinases). VP1 is not part of that perception/transduction core: the multi-omics synthesis explicitly places VP1 at the downstream ABI3 node of the PYL-ABI1-SnRK2-ABI3 module and classifies vp1 as a plant-specific transcription factor acting in ABA signaling, while UniProt describes VP1 as "potentiating the response to ABA." Its experimentally supported function is to regulate/potentiate the ABA-responsive transcriptional output (it co-activates ABRE/G-box maturation genes and is required for developmental ABA responsiveness of rab28), i.e. it regulates the pathway's effect rather than transducing perception. Genetic data place VP1 epistatic/downstream as an essential executor of the maturation/dormancy program. Therefore the annotation should be retained but MODIFIED to terms that capture VP1 as a regulator/effector of the ABA response: "regulation of abscisic acid-activated signaling pathway" (GO:0009787) and "cellular response to abscisic acid stimulus" (GO:0071215). The seed-maturation and germination-repression outputs are captured by the NEW process terms below.
Proposed replacements:
regulation of abscisic acid-activated signaling pathway
cellular response to abscisic acid stimulus
Supporting Evidence:
PMID:34834800
Both the vp1 and vp4 genes encode a plant-specific transcription factor involved in ABA signaling that can complement the Arabidopsis abi3 mutant allele
PMID:34834800
The ABA core signaling components (PYL-ABI1-SnRK2-ABI3) were affected in most of the mutants
PMID:1889090
Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response.
PMID:1837331
rab 28 mRNA has been identified as ABA-inducible in embryos and young leaves.
file:MAIZE/VP1/VP1-deep-research-falcon.md
**vp1** is classified as a plant-specific transcription factor acting in ABA signaling
file:MAIZE/VP1/VP1-deep-research-falcon.md
perturbation of the PYL-ABI1-SnRK2-ABI3 core module
file:MAIZE/VP1/VP1-deep-research-falcon.md
**ABA-dependent co-activation** of ABRE/G-box
|
|
GO:0010431
seed maturation
|
IMP
file:MAIZE/VP1/VP1-deep-research-falcon.md |
NEW |
Summary: VP1 is the master regulator of the maize seed maturation program (desiccation tolerance and dormancy). This core biological process is not represented in current GOA and should be added.
Reason: VP1 is genetically essential for the seed maturation program: vp1 loss-of-function mutants are viviparous, undergo precocious germination, lose desiccation tolerance, and show strongly reduced accumulation of multiple maturation-associated transcripts. Maize VP1 expressed in Arabidopsis abi3-6 restores green-seed/desiccation phenotypes, confirming a conserved seed-maturation function with ABI3. GO:0010431 (seed maturation) is the precise process term; IMP is justified by the vp1 mutant phenotype. (A regulatory term, GO:2000693 positive regulation of seed maturation, is an alternative, since VP1 promotes the program; the directly-involved seed-maturation term is used here as the primary annotation.)
Supporting Evidence:
PMID:1889090
The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development.
PMID:11737778
VP1 fully restores abscisic acid (ABA) sensitivity of abi3 during seed germination
file:MAIZE/VP1/VP1-deep-research-falcon.md
genetically essential for coordinating the **seed maturation program** (desiccation tolerance and dormancy) and for implementing **ABA-responsive transcription**
file:MAIZE/VP1/VP1-deep-research-falcon.md
Suppression of germination in maize kernels absolutely requires functional **Vp1**
|
|
GO:0010187
negative regulation of seed germination
|
IMP
file:MAIZE/VP1/VP1-deep-research-falcon.md |
NEW |
Summary: VP1 enforces seed dormancy and prevents precocious germination (vivipary); vp1 mutants germinate precociously on the ear. VP1 also directly represses germination-associated programs in aleurone.
Reason: The defining vp1 phenotype is vivipary - precocious germination of developing kernels on the ear - so VP1 normally negatively regulates germination and enforces the dormant state. VP1 represses germination-associated expression programs in maize aleurone (e.g. alpha-amylase), a separable function from its activation of maturation genes. GO:0010187 (negative regulation of seed germination) precisely captures this; IMP is justified by the viviparous mutant phenotype. The founding study established that Vp1 is required for the maturation program (whose enforcement suppresses germination), and the ABA-insensitive vp1 mutant fails to maintain the dormant maturation state, germinating precociously on the ear.
Supporting Evidence:
PMID:1889090
The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development.
file:MAIZE/VP1/VP1-deep-research-falcon.md
**Transcriptional repressor** of germination-associated expression programs in maize aleurone
file:MAIZE/VP1/VP1-deep-research-falcon.md
precocious germination
|
|
GO:0043565
sequence-specific DNA binding
|
IDA
file:MAIZE/VP1/VP1-deep-research-falcon.md |
NEW |
Summary: VP1's B3 domain binds DNA in a sequence-specific manner - directly recognizing the Sph element of the maize C1 promoter. This refines the generic GO:0003677 "DNA binding".
Reason: The deep-research synthesis describes direct B3-dependent activation of the maize C1 gene via binding to the Sph element, a defined cis-element, demonstrating sequence-specific (not generic) DNA binding by the B3 domain. GO:0043565 (sequence-specific DNA binding) is more informative than the generic GO:0003677 and reflects the established B3 recognition of a specific promoter motif. Caveat: this is restricted to a subset of targets - the founding study (McCarty et al. 1991) proposed VP1 "may bind to DNA indirectly" (UniProt FUNCTION) and the deep-research synthesis notes that VP1's co-activation and repression functions are largely B3-independent and partner- mediated, so sequence-specific binding should be regarded as target-specific (C1/Sph) rather than the dominant mode for all VP1 targets. Evidence is the promoter-binding/ activation reported for the Sph element; the cited deep-research summary aggregates the primary B3/Sph binding result.
Supporting Evidence:
file:MAIZE/VP1/VP1-deep-research-falcon.md
**Direct transcriptional activator** of some promoters via **B3 DNA binding**, exemplified by **maize *C1*** activation via B3 binding to the **Sph element**
file:MAIZE/VP1/VP1-deep-research-falcon.md
Direct activation of maize **C1** requires B3-mediated binding to the Sph element
|
Q: Does maize VP1 bind the Sph/RY cis-element directly and sequence-specifically in vitro, and what is the consensus B3 recognition motif, given that some VP1 activation and repression functions are reported to be B3-independent and partner-mediated?
Suggested experts: Donald R. McCarty
Q: Which bZIP/ABRE-binding partners does maize VP1 physically interact with to co-activate G-box/ABRE maturation genes, and are these interactions ABA-dependent?
Suggested experts: Masaharu Suzuki
Q: Is the cytoplasmic localization listed for VP1 a genuine regulated pool (e.g. nucleocytoplasmic shuttling) or an annotation artifact, given the absence of direct localization data for the maize protein?
Suggested experts: Donald R. McCarty
Experiment: Perform ChIP-seq and in vitro DNA-binding (EMSA/SELEX) for maize VP1 in developing embryos to define its direct genome-wide targets and the B3 recognition motif, and to distinguish direct B3-dependent targets (e.g. C1/Sph) from partner-mediated co-activated/repressed genes.
Hypothesis: VP1 directly and sequence-specifically binds Sph/RY-type elements at a subset of maturation gene promoters, while co-activation of ABRE/G-box genes is mediated by interaction with bZIP partners rather than direct VP1 DNA binding.
Type: ChIP-seq and in vitro DNA-binding assay
Experiment: Epistasis and reporter analyses placing VP1 relative to the core ABA module (ZmPYL receptors, ZmPP2Cs, ZmSnRK2s) - e.g. testing whether VP1 transcriptional output requires SnRK2 activity and whether VP1 acts downstream of SnRK2-mediated phosphorylation of ABF/AREB-type factors.
Hypothesis: VP1 acts as a downstream transcriptional effector that regulates/potentiates the ABA response, downstream of the PYR/PYL-PP2C-SnRK2 perception-transduction cascade, rather than as a component of that cascade.
Type: genetic epistasis and transactivation assay
Experiment: Generate a translational VP1-fluorescent-protein fusion expressed from the native promoter in maize and image its subcellular localization across embryo development, with fractionation, to test the curated cytoplasm vs nucleus assignment.
Hypothesis: VP1 is predominantly nuclear during seed maturation, consistent with its transcription-factor function, and any cytoplasmic signal reflects a minor or regulated population.
Type: live-cell fluorescence localization
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
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We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
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Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Maize Viviparous-1 (VP1; UniProt P26307; gene symbol Vp1) encodes a B3-domain transcriptional regulator that is genetically essential for coordinating the seed maturation program (desiccation tolerance and dormancy) and for implementing ABA-responsive transcription during embryogenesis. VP1 is functionally conserved with Arabidopsis ABI3 and acts through domain-modular transcriptional activation and repression, including direct promoter activation (e.g., C1) and ABA-dependent co-activation of ABRE/G-box–containing maturation genes (e.g., rab28). (suzuki2001maizevp1complements pages 1-2, pla1991regulationofthe pages 3-5, white1995molecularandphysiological pages 17-21)
The literature analyzed here consistently refers to maize viviparous-1 (Vp1/vp1) as an ABA-related seed regulator and as the ortholog of Arabidopsis ABI3, with a conserved B3 DNA-binding domain and additional conserved regions (A1/B1/B2). This matches the UniProt target identity P26307: “Regulatory protein viviparous-1” from **
Zea mays (maize), annotated with a B3 DNA-binding domain**. (suzuki2001maizevp1complements pages 1-2)
In maize, vivipary refers to precocious germination of developing kernels on the ear, reflecting failure to maintain the normal separation between maturation and germination programs. The vp1 mutant is classically described as ABA-insensitive and exhibits defects characteristic of a failed maturation program (precocious germination, loss of desiccation tolerance, and developmental mistiming such as green embryos). (suzuki2001maizevp1complements pages 1-2)
VP1/ABI3 proteins contain four prominent conserved domains, A1, B1, B2, and B3, where B3 is the DNA-binding domain. Functional analyses summarized in a key VP1 study distinguish at least three separable regulatory activities: (i) ABA-dependent co-activation of seed ABA-regulated genes via G-box/ABRE-related cis-elements, (ii) direct activation of certain targets via B3-dependent DNA binding (e.g., C1 via the Sph element), and (iii) repression of germination-associated genes in aleurone; the co-activation and repression functions are described as largely B3-independent and mediated by protein–protein interactions with other transcription factors. (suzuki2001maizevp1complements pages 1-2, suzuki2001maizevp1complements pages 6-7)
A central cis-regulatory theme in ABA-responsive transcription is the ABRE (ABA response element), often centered on a G-box core (CACGTG). A maize embryo-maturation synthesis notes VP1 can transactivate ABRE-containing promoters synergistically with ABA, and highlights the mechanistic relevance of ABRE-binding proteins (e.g., bZIP-type factors). (white1995molecularandphysiological pages 17-21)
Across primary and synthesis sources, VP1 functions as a transcriptional regulator (not an enzyme/transport protein):
- ABA-dependent co-activator for seed-specific ABA-regulated genes through G-box/ABRE-related elements. (suzuki2001maizevp1complements pages 1-2)
- Direct transcriptional activator of some promoters via B3 DNA binding, exemplified by maize C1 activation via B3 binding to the Sph element. (suzuki2001maizevp1complements pages 1-2)
- Transcriptional repressor of germination-associated expression programs in maize aleurone, likely via protein interactions. (suzuki2001maizevp1complements pages 1-2)
An embryo-maturation synthesis of maize hormonal control emphasizes that the developmental outcome is governed by ABA vs GA balance, but that preventing vivipary and enforcing maturation “absolutely requires” functional Vp1; reducing GA can suppress vivipary in ABA-deficient mutants, yet does not suppress vivipary when VP1 is nonfunctional, consistent with VP1 being epistatic/downstream as an essential executor of maturation/dormancy programs. (white1995molecularandphysiological pages 145-150, white1995molecularandphysiological pages 155-159, white1995molecularandphysiological pages 1-10)
A 2021 Plant Cell study (focused on maize seed development regulatory networks) provides direct evidence that ZmABI19 binds the Vp1 promoter (ChIP-seq and reporter assays), with ABA enhancing ZmABI19 transactivation of Vp1. This positions VP1 within a broader ABA-coupled transcriptional circuit coordinating embryo development and grain filling. In that work, Vp1 expression begins ~3–5 DAP and peaks around ~10 DAP, overlapping spatially with ZmABI19 signal in the scutellum. (yang2021theb3domaincontaining pages 16-17)
VP1 is described as a direct activator of the maize C1 gene; activation is mediated by B3 binding to the C1 promoter Sph element. This is among the clearest direct-target statements in the retrieved evidence. (suzuki2001maizevp1complements pages 1-2)
A primary 1991 study directly examines rab28 regulation in maize viviparous mutants:
- In vp1 (vpl) embryos, rab28 transcripts fail to accumulate to significant levels during embryogenesis, despite near-normal ABA levels in the mutant background—consistent with impaired developmental ABA responsiveness. (pla1991regulationofthe pages 1-2)
- Exogenous ABA (10 μM) can induce rab28 mRNA in young vp1 embryos (24 h), but this induction is reduced in older embryos, indicating partial bypass of VP1 dependence in a stage-dependent manner. (pla1991regulationofthe pages 3-5)
- The rab28 promoter contains an ABA-related motif CACGTGG (at ~-146) that confers ABA-dependent expression and binds nuclear protein, consistent with ABRE/G-box–centered transcriptional regulation logic. (pla1991regulationofthe pages 3-5)
A maize embryo-maturation synthesis reports multiple maturation-associated seed transcripts are strongly reduced in viviparous mutants, with quantitation indicating several messages reduced ≥4-fold in vp1 embryos (and some reduced up to ~10-fold), supporting VP1 as a global regulator of the maturation gene program rather than a single-pathway effector. (white1995molecularandphysiological pages 40-47)
A primary VP1-focused source summarizes vp1 mutants as having precocious germination, loss of desiccation tolerance, and an ABA-insensitive phenotype, and discusses developmental mistiming (e.g., green embryos in maturation program) consistent with a failure to enforce the seed maturation state. (suzuki2001maizevp1complements pages 1-2)
A landmark study demonstrates that 35S:VP1 expression in Arabidopsis abi3-6 can substantially restore ABI3-associated functions:
- A single 35S-VP1 copy can complement the green seed and desiccation intolerant phenotypes of abi3-6, and multiple lines fully restore ABA sensitivity during seed germination. (suzuki2001maizevp1complements pages 2-4)
- cab3-GUS repression is restored; C1-GUS is only partially restored (about ~20% of wild-type activity at seed maturity), highlighting separable VP1/ABI3 functions and possible partner specificity. (suzuki2001maizevp1complements pages 2-4, suzuki2001maizevp1complements pages 4-6)
- Ectopic VP1 in vegetative tissues causes ABA-related phenotypes and demonstrates ABA–auxin interaction in roots (auxin potentiating VP1-mediated ABA responses; ABA antagonizing auxin effects in the VP1 context). (suzuki2001maizevp1complements pages 4-6, suzuki2001maizevp1complements pages 6-7)
The retrieved evidence base strongly supports VP1 as a DNA-binding transcriptional regulator, which generally implies nuclear function, but explicit experimental subcellular localization (e.g., GFP fusion microscopy, fractionation) for maize VP1 was not found in the obtained texts. Therefore, this report does not make a definitive, experimentally sourced localization claim beyond nucleus-consistent function. (suzuki2001maizevp1complements pages 1-2, white1995molecularandphysiological pages 17-21)
Direct new biochemical characterization of maize VP1 itself is limited in the 2023–2024 sources retrieved; however, recent work strengthens the modern view of VP1/ABI3-like factors as central nodes in seed development and dormancy networks:
A 2024 review of transcription factors in embryogenesis highlights the continuing centrality of seed “master regulators” (including B3 family factors) across crops, reflecting sustained focus on networks that include ABI3/VP1-like regulators in cereal embryogenesis. (long2024thetranscriptionfactor pages 71-73)
A 2024 rice study on OsWRKY71 links early germination phenotypes and transcriptomic shifts to changes in ABA-associated networks including the VP1–SDR4–DOG1L dormancy branch, illustrating that VP1 (or orthologous nodes) remains a reference point for dormancy regulation in cereals. (long2024thetranscriptionfactor pages 71-73)
A 2024 maize preprint on ZmbZIP75 focuses on grain filling and dehydration and cites literature tying VP1 to seed maturation and ABA-related pathways, including VP1’s placement among key regulators influencing desiccation-associated outputs (e.g., raffinose-related metabolism via VP1-linked networks). While not a primary VP1 study, it exemplifies how VP1 is integrated into modern multi-factor seed regulatory models. (long2024thetranscriptionfactor pages 71-73)
The retrieved sources directly support VP1 as a master regulator of seed maturation/dormancy and ABA responsiveness, implying practical relevance for traits such as seed vigor, desiccation tolerance, and avoidance of precocious germination. (white1995molecularandphysiological pages 1-10, suzuki2001maizevp1complements pages 1-2)
However, within the documents successfully obtained here, direct evidence of deployed VP1-based breeding programs or validated field implementations in maize was not captured. The most application-proximal evidence in hand is the cross-species functional complementation (maize VP1 functioning in Arabidopsis), which supports feasibility of manipulating VP1/ABI3 nodes but is not itself a crop deployment. (suzuki2001maizevp1complements pages 2-4)
The following table consolidates key experimental evidence supporting VP1 functional annotation.
| Evidence type | Finding (domain/function/target/phenotype) | System/tissue/stage | Key experimental readout | Interpretation for VP1 function | Primary source (with year, journal, URL if available) | Citation ID |
|---|---|---|---|---|---|---|
| Molecular | VP1/ABI3 proteins contain four conserved domains (A1, B1, B2, B3); B3 is the DNA-binding domain | Comparative VP1/ABI3 protein analysis; maize VP1 discussed in seed context | Sequence/domain analysis summarized in functional study | Confirms that maize VP1 is a B3-domain transcription factor, matching UniProt P26307 annotation | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 1-2) |
| Molecular | VP1 co-activates seed-specific ABA-regulated genes, strongly ABA-dependent and mediated mainly via G-box-related cis-elements | Maize seed gene regulation; embryo/endosperm context | Functional analyses cited in review/introduction | Supports annotation of VP1 as an ABA-responsive transcriptional regulator rather than an enzyme or transporter | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 1-2) |
| Molecular | Direct activation of maize C1 requires B3-mediated binding to the Sph element | Maize promoter regulation | Promoter-binding/activation evidence summarized in paper | Establishes direct DNA-binding target specificity for at least one VP1-regulated promoter | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 1-2) |
| Molecular | VP1 represses germination-specific gene expression in aleurone; repression/co-activation functions do not require B3 and likely involve protein–protein interactions | Maize aleurone/endosperm | Domain-function dissection summarized in study | Indicates VP1 has separable activator and repressor functions, including indirect transcriptional regulation via partner proteins | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 6-7, suzuki2001maizevp1complements pages 1-2) |
| Genetic | vp1 mutants are ABA-insensitive, undergo precocious germination (vivipary), lose desiccation tolerance, and produce green embryos during maturation | Maize developing seeds/embryos | Mutant phenotype analysis | Strong genetic evidence that VP1 is essential for seed maturation, dormancy, and ABA responsiveness | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 1-2) |
| Genetic | Suppression of germination in maize kernels absolutely requires functional Vp1; GA reduction suppresses vivipary in ABA-deficient mutants but not in vp1 | Maize embryos during maturation/germination transition | Hormone/genetic interaction studies summarized in thesis | Places VP1 downstream of, or epistatic to, ABA/GA balance as an essential executor of maturation/dormancy | White, 1995, thesis/review source | (white1995molecularandphysiological pages 1-10, white1995molecularandphysiological pages 145-150, white1995molecularandphysiological pages 155-159) |
| Molecular | Multiple maturation-associated seed transcripts are strongly reduced in vp1 embryos; several are decreased ~4- to 10-fold, and one family ~10-fold specifically in vp1 | Maize maturing embryos (~30 DAP) | Northern/slot-blot analyses of cDNA families | VP1 is required for normal expression of a broad maturation gene program, including storage/LEA-like genes | White, 1995, thesis/review source | (white1995molecularandphysiological pages 40-47) |
| Molecular | rab28 mRNA is undetectable in young vp1 embryos and remains low in mature vp1 embryos despite near-normal ABA levels | Maize embryos during embryogenesis | Northern blots in viviparous mutants | VP1 is required for normal developmental ABA responsiveness of the LEA-like gene rab28 | Pla et al., 1991, Molecular and General Genetics, https://doi.org/10.1007/bf00280296 | (pla1991regulationofthe pages 3-5, pla1991regulationofthe pages 1-2) |
| Molecular | Exogenous ABA (10 μM, 24 h) can induce rab28 precociously in young vp1 embryos, but induction is reduced in older mutant embryos | Excised young vs older maize vp1 embryos | ABA treatment followed by Northern analysis | VP1 is not absolutely required for all ABA-induced rab28 expression, but is needed for full developmental competence and sustained endogenous regulation | Pla et al., 1991, Molecular and General Genetics, https://doi.org/10.1007/bf00280296 | (pla1991regulationofthe pages 3-5, pla1991regulationofthe pages 1-2) |
| Molecular | The rab28 promoter contains an ABA-related motif (CACGTGG at -146) that confers ABA-dependent expression and binds nuclear protein | Maize promoter assays | Promoter/motif analysis and nuclear protein binding | Supports a cis-regulatory basis for VP1-linked ABA control of rab28, likely via ABRE/G-box-centered transcription complexes | Pla et al., 1991, Molecular and General Genetics, https://doi.org/10.1007/bf00280296 | (pla1991regulationofthe pages 3-5) |
| Transgenic | 35S-driven maize VP1 partially complements Arabidopsis abi3-6; one copy restores green seed/desiccation-intolerant phenotypes and multiple lines fully restore ABA sensitivity of germination | Arabidopsis transgenic seeds expressing maize VP1 | Complementation of abi3 mutant phenotypes | Demonstrates functional conservation between maize VP1 and ABI3 and validates VP1 as a master seed maturation regulator | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 2-4, suzuki2001maizevp1complements pages 1-2) |
| Transgenic | 35S-VP1 restores repression of cab3-GUS and partially restores C1-GUS (~20% of wild type at seed maturity) in abi3-6 | Arabidopsis developing seeds | Reporter gene assays | Shows VP1 can mediate both repression and activation functions in planta, but activation is incomplete in a heterologous seed context | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 4-6, suzuki2001maizevp1complements pages 2-4, suzuki2001maizevp1complements pages 6-7) |
| Transgenic | 35S-VP1 enhances ABA inhibition of root growth, induces seed-specific CRC in leaves under ABA, and mediates ABA–auxin interaction in roots; ABA suppresses auxin-induced lateral roots in VP1-expressing plants | Arabidopsis vegetative tissues/roots | Root growth, reporter expression, and hormone treatment assays | Indicates VP1 can act outside seeds when ectopically expressed and integrates ABA with auxin-responsive developmental programs | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 1-2, suzuki2001maizevp1complements pages 4-6, suzuki2001maizevp1complements pages 6-7) |
| Molecular | Distinct VP1 domains are required for different outputs: Em/C1 activation vs α-amylase repression | Domain-function analysis summarized from maize work | Functional dissection summarized in discussion | Supports fine-grained annotation of VP1 as a modular transcriptional regulator with separable activation and repression activities | Suzuki et al., 2001, The Plant Journal, https://doi.org/10.1046/j.1365-313x.2001.01165.x | (suzuki2001maizevp1complements pages 6-7) |
| Molecular/regulatory network | ZmABI19 directly binds the Vp1 promoter; ABA enhances this transactivation, and Vp1 expression begins at 3–5 DAP and peaks around 10 DAP, overlapping with scutellum expression | Maize early seed development; embryo/scutellum | ChIP-seq, dual-luciferase, expression profiling | Places VP1 in an upstream ABA-responsive grain-filling/embryogenesis transcription network rather than as an isolated regulator | Yang et al., 2021, The Plant Cell, https://doi.org/10.1093/plcell/koaa008 | (yang2021theb3domaincontaining pages 16-17) |
| Molecular/regulatory network | ZmABI19 recognizes G-box4 in the Vp1 promoter, whereas it binds RY motifs in many other targets | Maize promoter regulation | ChIP-seq and promoter-element analysis | Consistent with B3/seed-factor regulatory logic and with VP1 participation in ABA-coupled LAFL-like seed developmental circuits | Yang et al., 2021, The Plant Cell, https://doi.org/10.1093/plcell/koaa008 | (yang2021theb3domaincontaining pages 16-17) |
| Genetic/omics | In maize vivipary datasets, vp1 is classified as a plant-specific transcription factor acting in ABA signaling; vivipary mutants show downregulation of NCED4, upregulation of GA3ox, and perturbation of the PYL-ABI1-SnRK2-ABI3 core module | Maize vivipary mutants, seed transcriptomes/metabolomes | Multi-omics comparison across seven vivipary mutants | Reinforces current systems-level view that VP1 functions within the ABA–GA antagonism network controlling dormancy vs germination | Wang et al., 2021, Plants, https://doi.org/10.3390/plants10112437 | (wang2021multiomicsanalysesreveal pages 1-2) |
Table: This table summarizes functional annotation evidence for maize viviparous-1 (VP1; UniProt P26307), covering domains, molecular functions, target genes, regulatory interactions, and mutant/transgenic phenotypes. It is restricted to findings directly supported by the cited context IDs from the preceding evidence collection.
References
(suzuki2001maizevp1complements pages 1-2): Masaharu Suzuki, Chien‐Yuan Kao, Suzy Cocciolone, and Donald R. McCarty. Maize vp1 complements arabidopsisabi3 and confers a novel aba/auxin interaction in roots. The Plant Journal, 28(4):409-418, Nov 2001. URL: https://doi.org/10.1046/j.1365-313x.2001.01165.x, doi:10.1046/j.1365-313x.2001.01165.x. This article has 186 citations.
(pla1991regulationofthe pages 3-5): Maria Pla, Jordi Gómez, Adela Goday, and Montserrat Pagès. Regulation of the abscisic acid-responsive gene rab28 in maize viviparous mutants. Molecular and General Genetics MGG, 230:394-400, Dec 1991. URL: https://doi.org/10.1007/bf00280296, doi:10.1007/bf00280296. This article has 129 citations.
(white1995molecularandphysiological pages 17-21): CN White. Molecular and physiological aspects of maize embryo maturation. Unknown journal, 1995.
(suzuki2001maizevp1complements pages 6-7): Masaharu Suzuki, Chien‐Yuan Kao, Suzy Cocciolone, and Donald R. McCarty. Maize vp1 complements arabidopsisabi3 and confers a novel aba/auxin interaction in roots. The Plant Journal, 28(4):409-418, Nov 2001. URL: https://doi.org/10.1046/j.1365-313x.2001.01165.x, doi:10.1046/j.1365-313x.2001.01165.x. This article has 186 citations.
(white1995molecularandphysiological pages 145-150): CN White. Molecular and physiological aspects of maize embryo maturation. Unknown journal, 1995.
(white1995molecularandphysiological pages 155-159): CN White. Molecular and physiological aspects of maize embryo maturation. Unknown journal, 1995.
(white1995molecularandphysiological pages 1-10): CN White. Molecular and physiological aspects of maize embryo maturation. Unknown journal, 1995.
(yang2021theb3domaincontaining pages 16-17): Taolan Yang, Liangxing Guo, Chen Ji, Haihai Wang, Jiechen Wang, Xixi Zheng, Qiao Xiao, and Yongrui Wu. The b3 domain-containing transcription factor zmabi19 coordinates expression of key factors required for maize seed development and grain filling. The Plant cell, 33 1:104-128, Mar 2021. URL: https://doi.org/10.1093/plcell/koaa008, doi:10.1093/plcell/koaa008. This article has 127 citations.
(pla1991regulationofthe pages 1-2): Maria Pla, Jordi Gómez, Adela Goday, and Montserrat Pagès. Regulation of the abscisic acid-responsive gene rab28 in maize viviparous mutants. Molecular and General Genetics MGG, 230:394-400, Dec 1991. URL: https://doi.org/10.1007/bf00280296, doi:10.1007/bf00280296. This article has 129 citations.
(white1995molecularandphysiological pages 40-47): CN White. Molecular and physiological aspects of maize embryo maturation. Unknown journal, 1995.
(suzuki2001maizevp1complements pages 2-4): Masaharu Suzuki, Chien‐Yuan Kao, Suzy Cocciolone, and Donald R. McCarty. Maize vp1 complements arabidopsisabi3 and confers a novel aba/auxin interaction in roots. The Plant Journal, 28(4):409-418, Nov 2001. URL: https://doi.org/10.1046/j.1365-313x.2001.01165.x, doi:10.1046/j.1365-313x.2001.01165.x. This article has 186 citations.
(suzuki2001maizevp1complements pages 4-6): Masaharu Suzuki, Chien‐Yuan Kao, Suzy Cocciolone, and Donald R. McCarty. Maize vp1 complements arabidopsisabi3 and confers a novel aba/auxin interaction in roots. The Plant Journal, 28(4):409-418, Nov 2001. URL: https://doi.org/10.1046/j.1365-313x.2001.01165.x, doi:10.1046/j.1365-313x.2001.01165.x. This article has 186 citations.
(long2024thetranscriptionfactor pages 71-73): Tiandan Long, Yayun Wang, Jin Yang, Zhou Liu, Changqing Mao, Yufeng Hu, Junjie Zhang, Hanmei Liu, Yinghong Liu, Xiujun Fan, Lei Gao, Huanhuan Huang, Ying Xie, Daqiu Zhao, Yubi Huang, and Yangping Li. The transcription factor zmbzip75 promotes both grain filling and kernel dehydration in maize. BioRxiv, Sep 2024. URL: https://doi.org/10.1101/2024.09.11.612493, doi:10.1101/2024.09.11.612493. This article has 3 citations.
(wang2021multiomicsanalysesreveal pages 1-2): Yiru A. Wang, Junli Zhang, Minghao Sun, Cheng He, K. Yu, Bing Zhao, Rui Li, Jian Li, Zongying Yang, Xiao Wang, Haiyan Duan, Junjie Fu, Sanzhen Liu, Xuebin Zhang, and Jun Zheng. Multi-omics analyses reveal systemic insights into maize vivipary. Plants, 10:2437, Nov 2021. URL: https://doi.org/10.3390/plants10112437, doi:10.3390/plants10112437. This article has 12 citations.
id: P26307
gene_symbol: VP1
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:4577
label: Zea mays
description: >
Maize VIVIPAROUS-1 (VP1; UniProt P26307) is a seed-specific B3-domain transcriptional
regulator and the maize ortholog of Arabidopsis ABI3. It is genetically essential for
coordinating the seed maturation program (acquisition of desiccation tolerance and
dormancy) and for implementing ABA-responsive transcription during embryogenesis
(deep-research falcon report; Suzuki et al. 2001, Pla et al. 1991, White 1995). VP1 is a
modular transcription factor: it acts as (i) an ABA-dependent co-activator of seed
ABA-regulated maturation genes via G-box/ABRE-related cis-elements (e.g. Em, rab28),
(ii) a direct, B3-dependent sequence-specific DNA-binding activator of certain promoters
(the maize anthocyanin regulator C1 via the Sph element), and (iii) a repressor of
germination-associated programs in aleurone (e.g. alpha-amylase), with the co-activation
and repression functions largely B3-independent and mediated by protein-protein
interactions. The protein contains four conserved domains (A1, B1, B2 and the C-terminal
B3 DNA-binding domain spanning residues 517-619) and an N-terminal acidic/disordered
transcriptional-activation region. Loss-of-function vp1 mutants are ABA-insensitive and
viviparous - they undergo precocious germination on the ear, fail to acquire desiccation
tolerance, and lose normal accumulation of LEA/maturation transcripts; maize VP1 expressed
in Arabidopsis abi3-6 restores green-seed/desiccation phenotypes and ABA sensitivity,
demonstrating functional conservation with ABI3. A central nuance for GO annotation is
that VP1 is a downstream transcriptional EFFECTOR that mediates and potentiates ABA
responses (it sits at the terminal ABI3 node of the PYL-ABI1-SnRK2-ABI3 module), rather
than being a component of the core PYR/PYL-PP2C-SnRK2 perception-to-transduction cascade
(GO:0009738). VP1 function is nuclear (consistent with its DNA-binding transcriptional
regulator role), though no direct experimental subcellular-localization assay for the
maize protein was found in the retrieved literature; UniProt also lists a cytoplasmic
location.
existing_annotations:
# --- Current GOA annotations (2026 release) ---
- term:
id: GO:0003677
label: DNA binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >
IEA annotation from InterPro (IPR003340, B3 DNA-binding domain). VP1 contains a
C-terminal B3 DNA-binding domain (residues 517-619) and binds DNA directly - it
activates the maize C1 promoter via B3 binding to the Sph element.
action: ACCEPT
reason: >
Correct and core. The UniProt feature table annotates a TF-B3 DNA-binding domain at
517-619, and the deep-research synthesis confirms that VP1/ABI3 proteins contain four
conserved domains in which B3 is the DNA-binding domain, with direct B3-dependent
binding to the C1 promoter Sph element. "DNA binding" is generic but not incorrect;
the more informative sequence-specific DNA-binding transcription factor activity is
captured by GO:0003700 (modified below). Note that the founding study (McCarty et al.
1991) localized VP1's transactivation activity to an acidic domain and proposed that
VP1 "may bind to DNA indirectly" for several targets (UniProt FUNCTION), so generic DNA
binding rather than direct sequence-specific binding is the safe MF claim for the bulk
of VP1 targets; direct B3-mediated binding is documented specifically for C1/Sph.
supported_by:
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "VP1/ABI3 proteins contain four prominent conserved domains, **A1, B1, B2, and B3**, where **B3 is the DNA-binding domain**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**maize *C1*** activation via B3 binding to the **Sph element**"
- reference_id: PMID:1889090
supporting_text: "An acidic transcriptional activation sequence was identified by fusion to the GAL4 DNA-binding domain."
- term:
id: GO:0003700
label: DNA-binding transcription factor activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >
IEA annotation from InterPro (IPR044800, LEC2-like B3 family) for sequence-specific
DNA-binding transcription factor activity. This is VP1's core molecular function - it
is a transcriptional regulator that activates and represses plant nuclear (RNA Pol II)
protein-coding genes. The generic term is correct but can be made more precise.
action: MODIFY
reason: >
VP1 is unambiguously a sequence-specific DNA-binding transcription factor: it acts as
a direct transcriptional activator of certain promoters via B3 DNA binding (C1 via the
Sph element), as an ABA-dependent co-activator of seed maturation genes via G-box/ABRE
elements, and as a repressor of germination genes. UniProt's original description (Cell
1991) is "a novel transcriptional activator." Because VP1 regulates RNA polymerase II
protein-coding genes, the generic GO:0003700 is better represented by the more specific
child term GO:0000981 (DNA-binding transcription factor activity, RNA polymerase
II-specific). The essence is correct; only the level of specificity is refined.
proposed_replacement_terms:
- id: GO:0000981
label: DNA-binding transcription factor activity, RNA polymerase II-specific
supported_by:
- reference_id: PMID:1889090
supporting_text: "Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response."
- reference_id: PMID:1889090
supporting_text: "Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "VP1 functions as a **transcriptional regulator** (not an enzyme/transport protein)"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**Direct transcriptional activator** of some promoters via **B3 DNA binding**, exemplified by **maize *C1*** activation via B3 binding to the **Sph element**"
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: >
IEA annotation from the UniProt subcellular-location vocabulary. VP1 is a DNA-binding
transcriptional regulator, so a nuclear location is where it carries out its function.
action: ACCEPT
reason: >
Consistent with VP1's molecular function. The deep-research synthesis states that the
evidence base strongly supports VP1 as a DNA-binding transcriptional regulator, which
generally implies nuclear function, and UniProt lists Nucleus as a subcellular
location. No direct GFP/fractionation experiment for maize VP1 was found in the
retrieved texts, but nuclear localization is the functionally relevant location for a
transcription factor and is accepted. VP1 strongly transactivates a target promoter
when expressed in maize protoplasts (McCarty et al. 1991), an activity that requires
access to the nuclear transcription machinery and is consistent with nuclear function.
supported_by:
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "The retrieved evidence base strongly supports VP1 as a **DNA-binding transcriptional regulator**, which generally implies nuclear function"
- reference_id: PMID:1889090
supporting_text: "Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene."
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: >
IEA annotation from the UniProt subcellular-location vocabulary (UniProt lists both
Cytoplasm and Nucleus). VP1 carries out its function as a transcription factor in the
nucleus; the cytoplasmic assignment is not where its core activity occurs.
action: KEEP_AS_NON_CORE
reason: >
The UniProt record lists Cytoplasm as a subcellular location, so the annotation is
retained, but it does not represent VP1's core, functionally relevant compartment. The
deep-research synthesis explicitly notes that no direct experimental subcellular
localization assay (GFP fusion, fractionation) for maize VP1 was found, and that the
evidence supports a nucleus-consistent function. A cytoplasmic pool would at most
reflect a shuttling/storage population rather than the site of VP1's transcriptional
activity. Marked non-core; not removed because it is a curated UniProt location.
supported_by:
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**explicit experimental subcellular localization (e.g., GFP fusion microscopy, fractionation)** for maize VP1 **was not found in the obtained texts**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "this report does not make a definitive, experimentally sourced localization claim beyond nucleus-consistent function"
- term:
id: GO:0006355
label: regulation of DNA-templated transcription
evidence_type: IEA
original_reference_id: GO_REF:0000108
qualifier: involved_in
review:
summary: >
IEA annotation inferred logically from the DNA-binding transcription factor activity
MF. VP1 regulates transcription of seed maturation and germination genes - primarily
as an activator of ABA-inducible maturation genes (Em, rab28, C1) and as a repressor
of germination-associated genes. The generic process term can be made more specific.
action: MODIFY
reason: >
VP1 is genuinely a transcriptional regulator, so the term is correct, but it is the
broad parent. VP1 regulates RNA polymerase II protein-coding genes and is described
primarily as a transcriptional activator that potentiates ABA-responsive maturation
gene expression (it can transactivate ABRE-containing promoters synergistically with
ABA and directly activates C1). The more informative child term is GO:0045944 (positive
regulation of transcription by RNA polymerase II). VP1 also has a separable repressor
function on germination genes (alpha-amylase), which is captured separately by the
proposed negative-regulation-of-germination process term below.
proposed_replacement_terms:
- id: GO:0045944
label: positive regulation of transcription by RNA polymerase II
supported_by:
- reference_id: PMID:1889090
supporting_text: "Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene."
- reference_id: PMID:1837331
supporting_text: "The results obtained with the ABA-insensitive vp1 mutant show that rab 28 transcripts do not accumulate to a significant level during embryogenesis."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "VP1 can **transactivate ABRE-containing promoters** synergistically with ABA"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "Distinct VP1 domains are required for different outputs: Em/C1 activation vs α-amylase repression"
# --- SPKW keyword-mapping annotation (GO_REF:0000043) ---
# Present in the Sept 2025 goa_uniprot_gcrp snapshot (go-db plant.ddb); REMOVED from the
# current (2026) GOA release when GOA retired the keyword2GO pipeline for cellular
# organisms. Reviewed retrospectively to assess whether removal was justified. Derived
# from the UniProt keyword "Abscisic acid signaling pathway".
- term:
id: GO:0009738
label: abscisic acid-activated signaling pathway
evidence_type: IEA
original_reference_id: GO_REF:0000043
retired: true
qualifier: involved_in
review:
summary: >
SPKW (GO_REF:0000043) annotation derived from the UniProt keyword "Abscisic acid
signaling pathway"; snapshot-only, removed in the current GOA release. VP1's genuine
ABA role is real and central, but it is a downstream transcriptional EFFECTOR that
mediates/potentiates ABA responses (the terminal ABI3 node of the
PYL-ABI1-SnRK2-ABI3 module) rather than a component of the core PYR/PYL-PP2C-SnRK2
perception-to-transduction cascade that GO:0009738 denotes.
action: MODIFY
reason: >
GOA's removal of the bare keyword term was partly justified but should not lose the
genuine biology. GO:0009738 (abscisic acid-activated signaling pathway) denotes the
ABA perception-to-transduction cascade (PYR/PYL receptors, PP2C phosphatases, SnRK2
kinases). VP1 is not part of that perception/transduction core: the multi-omics
synthesis explicitly places VP1 at the downstream ABI3 node of the PYL-ABI1-SnRK2-ABI3
module and classifies vp1 as a plant-specific transcription factor acting in ABA
signaling, while UniProt describes VP1 as "potentiating the response to ABA." Its
experimentally supported function is to regulate/potentiate the ABA-responsive
transcriptional output (it co-activates ABRE/G-box maturation genes and is required
for developmental ABA responsiveness of rab28), i.e. it regulates the pathway's effect
rather than transducing perception. Genetic data place VP1 epistatic/downstream as an
essential executor of the maturation/dormancy program. Therefore the annotation should
be retained but MODIFIED to terms that capture VP1 as a regulator/effector of the ABA
response: "regulation of abscisic acid-activated signaling pathway" (GO:0009787) and
"cellular response to abscisic acid stimulus" (GO:0071215). The seed-maturation and
germination-repression outputs are captured by the NEW process terms below.
proposed_replacement_terms:
- id: GO:0009787
label: regulation of abscisic acid-activated signaling pathway
- id: GO:0071215
label: cellular response to abscisic acid stimulus
supported_by:
- reference_id: PMID:34834800
supporting_text: "Both the vp1 and vp4 genes encode a plant-specific transcription factor involved in ABA signaling that can complement the Arabidopsis abi3 mutant allele"
- reference_id: PMID:34834800
supporting_text: "The ABA core signaling components (PYL-ABI1-SnRK2-ABI3) were affected in most of the mutants"
- reference_id: PMID:1889090
supporting_text: "Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response."
- reference_id: PMID:1837331
supporting_text: "rab 28 mRNA has been identified as ABA-inducible in embryos and young leaves."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**vp1** is classified as a plant-specific transcription factor acting in ABA signaling"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "perturbation of the PYL-ABI1-SnRK2-ABI3 core module"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**ABA-dependent co-activation** of ABRE/G-box"
# --- NEW annotations proposed from the literature ---
- term:
id: GO:0010431
label: seed maturation
evidence_type: IMP
original_reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
review:
summary: >
VP1 is the master regulator of the maize seed maturation program (desiccation
tolerance and dormancy). This core biological process is not represented in current
GOA and should be added.
action: NEW
reason: >
VP1 is genetically essential for the seed maturation program: vp1 loss-of-function
mutants are viviparous, undergo precocious germination, lose desiccation tolerance,
and show strongly reduced accumulation of multiple maturation-associated transcripts.
Maize VP1 expressed in Arabidopsis abi3-6 restores green-seed/desiccation phenotypes,
confirming a conserved seed-maturation function with ABI3. GO:0010431 (seed maturation)
is the precise process term; IMP is justified by the vp1 mutant phenotype. (A
regulatory term, GO:2000693 positive regulation of seed maturation, is an alternative,
since VP1 promotes the program; the directly-involved seed-maturation term is used
here as the primary annotation.)
supported_by:
- reference_id: PMID:1889090
supporting_text: "The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development."
- reference_id: PMID:11737778
supporting_text: "VP1 fully restores abscisic acid (ABA) sensitivity of abi3 during seed germination"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "genetically essential for coordinating the **seed maturation program** (desiccation tolerance and dormancy) and for implementing **ABA-responsive transcription**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "Suppression of germination in maize kernels absolutely requires functional **Vp1**"
- term:
id: GO:0010187
label: negative regulation of seed germination
evidence_type: IMP
original_reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
review:
summary: >
VP1 enforces seed dormancy and prevents precocious germination (vivipary); vp1 mutants
germinate precociously on the ear. VP1 also directly represses germination-associated
programs in aleurone.
action: NEW
reason: >
The defining vp1 phenotype is vivipary - precocious germination of developing kernels
on the ear - so VP1 normally negatively regulates germination and enforces the dormant
state. VP1 represses germination-associated expression programs in maize aleurone (e.g.
alpha-amylase), a separable function from its activation of maturation genes. GO:0010187
(negative regulation of seed germination) precisely captures this; IMP is justified by
the viviparous mutant phenotype. The founding study established that Vp1 is required for
the maturation program (whose enforcement suppresses germination), and the ABA-insensitive
vp1 mutant fails to maintain the dormant maturation state, germinating precociously on the
ear.
supported_by:
- reference_id: PMID:1889090
supporting_text: "The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**Transcriptional repressor** of germination-associated expression programs in maize aleurone"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "precocious germination"
- term:
id: GO:0043565
label: sequence-specific DNA binding
evidence_type: IDA
original_reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
review:
summary: >
VP1's B3 domain binds DNA in a sequence-specific manner - directly recognizing the Sph
element of the maize C1 promoter. This refines the generic GO:0003677 "DNA binding".
action: NEW
reason: >
The deep-research synthesis describes direct B3-dependent activation of the maize C1
gene via binding to the Sph element, a defined cis-element, demonstrating
sequence-specific (not generic) DNA binding by the B3 domain. GO:0043565
(sequence-specific DNA binding) is more informative than the generic GO:0003677 and
reflects the established B3 recognition of a specific promoter motif. Caveat: this is
restricted to a subset of targets - the founding study (McCarty et al. 1991) proposed
VP1 "may bind to DNA indirectly" (UniProt FUNCTION) and the deep-research synthesis notes
that VP1's co-activation and repression functions are largely B3-independent and partner-
mediated, so sequence-specific binding should be regarded as target-specific (C1/Sph)
rather than the dominant mode for all VP1 targets. Evidence is the promoter-binding/
activation reported for the Sph element; the cited deep-research summary aggregates the
primary B3/Sph binding result.
supported_by:
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**Direct transcriptional activator** of some promoters via **B3 DNA binding**, exemplified by **maize *C1*** activation via B3 binding to the **Sph element**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "Direct activation of maize **C1** requires B3-mediated binding to the Sph element"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings:
- statement: InterPro-to-GO mappings (IPR003340 B3 DNA-binding domain; IPR044800 LEC2-like)
assign DNA binding and DNA-binding transcription factor activity to VP1, consistent
with its experimentally supported role as a B3-domain transcriptional regulator.
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
findings:
- statement: UniProt subcellular-location mapping assigns Nucleus and Cytoplasm to VP1;
the nucleus is the functionally relevant compartment for this transcription factor,
whereas no direct localization experiment for maize VP1 was found in the literature.
- id: GO_REF:0000108
title: Automatic assignment of GO terms using logical inference, based on inter-ontology
links
findings:
- statement: Logical inference from the DNA-binding transcription factor activity MF
assigns the broad "regulation of DNA-templated transcription" process; VP1's specific
role is better captured by positive regulation of RNA Pol II transcription.
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings:
- statement: SwissProt keyword-derived (SPKW) annotation present in the Sept 2025
goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired
the keyword2GO pipeline for cellular organisms.
- statement: For VP1, the keyword "Abscisic acid signaling pathway" mapped to GO:0009738
(the perception-to-transduction cascade); VP1 is a downstream transcriptional effector
that regulates/potentiates ABA responses rather than a component of the core cascade,
so the term is better replaced by regulation-of/response-to ABA terms.
- id: file:MAIZE/VP1/VP1-deep-research-falcon.md
title: Deep-research report (falcon / Edison Scientific Literature) - functional
annotation of maize VP1 (P26307).
findings:
- statement: VP1 is a B3-domain transcriptional regulator essential for the seed
maturation program (desiccation tolerance, dormancy) and for ABA-responsive
transcription during embryogenesis; it is the maize ortholog of Arabidopsis ABI3.
- statement: VP1 is a modular transcription factor acting as an ABA-dependent co-activator
of seed maturation genes via G-box/ABRE elements, a direct B3-dependent
sequence-specific activator of C1 via the Sph element, and a repressor of
germination-associated genes (alpha-amylase) in aleurone.
- statement: vp1 mutants are ABA-insensitive and viviparous (precocious germination, loss
of desiccation tolerance); maize VP1 complements Arabidopsis abi3-6, restoring
green-seed/desiccation phenotypes and ABA sensitivity of germination.
- statement: Multi-omics analysis classifies vp1 as a plant-specific transcription factor
acting in ABA signaling and places VP1 at the downstream ABI3 node of the
PYL-ABI1-SnRK2-ABI3 core module, downstream of ABA perception/transduction.
- statement: VP1 is required for normal developmental ABA responsiveness of rab28; rab28
transcripts fail to accumulate in vp1 embryos despite near-normal ABA levels, though
exogenous ABA can partially induce rab28 in young vp1 embryos.
- statement: No direct experimental subcellular-localization assay for maize VP1 was found;
the report supports a nucleus-consistent function for the DNA-binding transcriptional
regulator.
- id: PMID:1889090
title: The Viviparous-1 developmental gene of maize encodes a novel transcriptional
activator.
findings:
- statement: The maize Vp1 gene is specifically required for expression of the maturation
program in seed development and encodes a 73,335 Da protein; an acidic transcriptional
activation sequence was identified by fusion to the GAL4 DNA-binding domain.
- statement: Expression of VP1 in maize protoplasts strongly activated (>130-fold) a
reporter gene fused to the promoter of a presumptive target gene, and the acidic domain
was essential and replaceable by the HSV VP16 activator; VP1 is a novel transcription
factor possibly involved in potentiation of a seed-specific hormone (ABA) response.
- id: PMID:11737778
title: Maize VP1 complements Arabidopsis abi3 and confers a novel ABA/auxin interaction
in roots.
findings:
- statement: 35S-driven maize VP1 partially complements the Arabidopsis abi3-6 deletion
allele - producing near-wild-type seed, fully restoring ABA sensitivity during seed
germination, and suppressing the abi3 early-flowering phenotype - demonstrating
functional orthology of VP1 with ABI3 as a seed-maturation regulator.
- statement: VP1/ABI3 activation functions are only partially complemented (CRC and C1-GUS
activation are markedly lower than wild type), and ectopic VP1 confers a novel ABA-auxin
interaction in roots, consistent with VP1 acting as a modular transcriptional regulator.
- id: PMID:1837331
title: Regulation of the abscisic acid-responsive gene rab28 in maize viviparous mutants.
findings:
- statement: In the ABA-insensitive vp1 mutant, rab28 transcripts fail to accumulate to a
significant level during embryogenesis, showing VP1 is required for normal developmental
ABA-responsive expression of the LEA-like rab28 gene.
- statement: rab28 mRNA is ABA-inducible in embryos and young leaves, and its proximal
promoter contains the conserved ABA-response element CACGTGG; exogenous ABA can partially
induce rab28 in young vp1 embryos, indicating stage-dependent partial bypass of VP1.
- id: PMID:33751093
title: The B3 domain-containing transcription factor ZmABI19 coordinates expression of key
factors required for maize seed development and grain filling.
findings:
- statement: ZmABI19, a B3-domain transcription factor, directly binds and regulates
Viviparous1 in the embryo as part of a grain-filling/seed-development regulatory network,
placing VP1 within an ABA-coupled transcriptional circuit.
- id: PMID:34834800
title: Multi-Omics Analyses Reveal Systemic Insights into Maize Vivipary.
findings:
- statement: Both vp1 and vp4 encode a plant-specific transcription factor involved in ABA
signaling that can complement the Arabidopsis abi3 mutant allele; multi-omics analysis
of vivipary mutants found the ABA core signaling components (PYL-ABI1-SnRK2-ABI3) were
affected, placing VP1 at the downstream ABI3 node rather than in ABA perception.
core_functions:
- description: >
VP1 is a sequence-specific B3-domain DNA-binding transcription factor that activates
transcription of ABA-responsive seed maturation genes. It directly binds the Sph element
of the maize C1 promoter via its B3 domain and acts as an ABA-dependent co-activator of
G-box/ABRE-containing maturation genes (e.g. Em, rab28).
molecular_function:
id: GO:0000981
label: DNA-binding transcription factor activity, RNA polymerase II-specific
directly_involved_in:
- id: GO:0045944
label: positive regulation of transcription by RNA polymerase II
locations:
- id: GO:0005634
label: nucleus
supported_by:
- reference_id: PMID:1889090
supporting_text: "Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**Direct transcriptional activator** of some promoters via **B3 DNA binding**, exemplified by **maize *C1*** activation via B3 binding to the **Sph element**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "VP1 can **transactivate ABRE-containing promoters** synergistically with ABA"
- description: >
VP1 is the master regulator of the maize seed maturation program, promoting acquisition
of desiccation tolerance and dormancy and mediating/potentiating ABA responses
downstream of ABA perception. Loss of VP1 causes ABA-insensitivity and vivipary.
molecular_function:
id: GO:0000981
label: DNA-binding transcription factor activity, RNA polymerase II-specific
directly_involved_in:
- id: GO:0010431
label: seed maturation
- id: GO:0009787
label: regulation of abscisic acid-activated signaling pathway
locations:
- id: GO:0005634
label: nucleus
supported_by:
- reference_id: PMID:1889090
supporting_text: "The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development."
- reference_id: PMID:34834800
supporting_text: "Both the vp1 and vp4 genes encode a plant-specific transcription factor involved in ABA signaling that can complement the Arabidopsis abi3 mutant allele"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "genetically essential for coordinating the **seed maturation program** (desiccation tolerance and dormancy) and for implementing **ABA-responsive transcription**"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**vp1** is classified as a plant-specific transcription factor acting in ABA signaling"
- description: >
VP1 enforces seed dormancy and prevents precocious germination (vivipary), in part by
repressing germination-associated transcriptional programs in the aleurone (e.g.
alpha-amylase), a function separable from its activation of maturation genes.
molecular_function:
id: GO:0000981
label: DNA-binding transcription factor activity, RNA polymerase II-specific
directly_involved_in:
- id: GO:0010187
label: negative regulation of seed germination
locations:
- id: GO:0005634
label: nucleus
supported_by:
- reference_id: PMID:1889090
supporting_text: "The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development."
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "**Transcriptional repressor** of germination-associated expression programs in maize aleurone"
- reference_id: file:MAIZE/VP1/VP1-deep-research-falcon.md
supporting_text: "Suppression of germination in maize kernels absolutely requires functional **Vp1**"
proposed_new_terms: []
suggested_questions:
- question: Does maize VP1 bind the Sph/RY cis-element directly and sequence-specifically
in vitro, and what is the consensus B3 recognition motif, given that some VP1 activation
and repression functions are reported to be B3-independent and partner-mediated?
experts:
- Donald R. McCarty
- question: Which bZIP/ABRE-binding partners does maize VP1 physically interact with to
co-activate G-box/ABRE maturation genes, and are these interactions ABA-dependent?
experts:
- Masaharu Suzuki
- question: Is the cytoplasmic localization listed for VP1 a genuine regulated pool (e.g.
nucleocytoplasmic shuttling) or an annotation artifact, given the absence of direct
localization data for the maize protein?
experts:
- Donald R. McCarty
suggested_experiments:
- description: Perform ChIP-seq and in vitro DNA-binding (EMSA/SELEX) for maize VP1 in
developing embryos to define its direct genome-wide targets and the B3 recognition motif,
and to distinguish direct B3-dependent targets (e.g. C1/Sph) from partner-mediated
co-activated/repressed genes.
hypothesis: VP1 directly and sequence-specifically binds Sph/RY-type elements at a subset
of maturation gene promoters, while co-activation of ABRE/G-box genes is mediated by
interaction with bZIP partners rather than direct VP1 DNA binding.
experiment_type: ChIP-seq and in vitro DNA-binding assay
- description: Epistasis and reporter analyses placing VP1 relative to the core ABA module
(ZmPYL receptors, ZmPP2Cs, ZmSnRK2s) - e.g. testing whether VP1 transcriptional output
requires SnRK2 activity and whether VP1 acts downstream of SnRK2-mediated phosphorylation
of ABF/AREB-type factors.
hypothesis: VP1 acts as a downstream transcriptional effector that regulates/potentiates
the ABA response, downstream of the PYR/PYL-PP2C-SnRK2 perception-transduction cascade,
rather than as a component of that cascade.
experiment_type: genetic epistasis and transactivation assay
- description: Generate a translational VP1-fluorescent-protein fusion expressed from the
native promoter in maize and image its subcellular localization across embryo
development, with fractionation, to test the curated cytoplasm vs nucleus assignment.
hypothesis: VP1 is predominantly nuclear during seed maturation, consistent with its
transcription-factor function, and any cytoplasmic signal reflects a minor or regulated
population.
experiment_type: live-cell fluorescence localization