Phytochrome control of photomorphogenesis (phyA/phyB - PIF - COP1/SPA - HY5)

Red and far-red light control seedling de-etiolation and growth in Arabidopsis thaliana through the phytochrome photoreceptors. In darkness two repressor systems keep seedlings etiolated: the PIF bHLH transcription factors (PIF1, PIF3, PIF4 and relatives) promote skotomorphogenic growth and repress chlorophyll biosynthesis and germination, and the nuclear CUL4-DDB1-COP1-SPA E3 ubiquitin ligase targets photomorphogenesis-promoting transcription factors such as HY5 for proteasomal degradation. Light converts phytochromes to the active Pfr form, phyB mainly under red light and phyA under far-red light. Pfr phytochromes enter the nucleus and form photobodies, where they act on both repressor systems. (1) They bind PIFs through APB and APA motifs. This triggers rapid PIF phosphorylation, with SPA1 kinase activity contributing in a phyB-PIF1-SPA1 complex, followed by ubiquitination and proteasomal degradation; PIF1 is turned over through the CUL4-COP1-SPA ligase. (2) They bind SPA proteins and disrupt the COP1-SPA interaction, which inactivates the ligase. HY5 then accumulates and, with the loss of PIF activity, drives photomorphogenic gene expression: hypocotyl growth inhibition, cotyledon expansion and greening. In darkness PIF1 also enhances COP1 E3 activity, so the two repressor systems act synergistically. Blue-light cryptochromes (CRY1) inhibit the same COP1-SPA node and are included only as a converging input. UVR8, PIF-independent phyB outputs, thermomorphogenesis (PIF4-temperature), photoperiodic flowering (COP1-SPA-CO) and hormone crosstalk are outside the module boundary.

MODULE:phytochrome_photomorphogenesisDRAFTCONCRETESignaling Pathwaymodules/phytochrome_photomorphogenesis.yaml
red or far-red light signaling pathwayGO:0010017 photomorphogenesisGO:0009640
PMID:25744387
Red-light-dependent interaction of phyB with SPA1 promotes COP1-SPA1 dissociation and photomorphogenic development in Arabidopsis.
Phytochromes promote photomorphogenesis through two arms, PIF degradation and suppression of COP1.
Phytochromes promote photomorphogenic developments upon light irradiation via a signaling pathway that involves rapid degradation of PIFs (PHYTOCHROME INTERACTING FACTORS) and suppression of COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) nuclear accumulation
PMID:25627066
Light-activated phytochrome A and B interact with members of the SPA family to promote photomorphogenesis in Arabidopsis by reorganizing the COP1/SPA complex.
Light-activated phyA and phyB bind SPA proteins in nuclear bodies and disrupt the COP1-SPA interaction.
light-activated phyA and phyB disrupt the interaction between COP1 and SPAs, resulting in reorganization of the COP1/SPA complex in planta
PMID:24858936
PHYTOCHROME INTERACTING FACTOR1 Enhances the E3 Ligase Activity of CONSTITUTIVE PHOTOMORPHOGENIC1 to Synergistically Repress Photomorphogenesis in Arabidopsis.
PIFs and COP1-SPA synergistically repress photomorphogenesis in darkness, with HY5 as the shared output.
In response to light, the phytochrome family of sensory photoreceptors simultaneously inactivates COP1-SPA complexes and induces the rapid degradation of PIFs to promote photomorphogenesis
PMID:23708772
Phytochrome-interacting factors have both shared and distinct biological roles.
Light-activated phytochromes enter the nucleus and promote PIF degradation.
Their activities are post-translationally countered by light-activated phytochromes, which promote the degradation of PIFs

Concrete Arabidopsis instance. Gene reviews owned in this curation batch are SPA1, PIF1 and PHYA; PHYB, PIF3, PIF4, COP1, HY5 and CRY1 reviews were read but not edited. Annoton functions follow each gene review's core_functions. SPA1 has two annotons because it has two separable roles: COP1 activator in the ligase node and PIF1 kinase in the PIF node. PIF1 likewise has two annotons: its DNA-binding transcription factor activity and its COP1 cofactor activity (ubiquitin-protein transferase activator, PMID:24858936), which carries the PIF-to-ligase POSITIVELY_REGULATES connection. SPA1 kinase activity (PIF1, PMID:31527679; also HY5 Ser36, PMID:33686674) comes from one research group, and PMID:27310313 proposes a structural role for the kinase-like domain. HY5 phosphorylation by SPA is not modelled as a separate connection. CRY1 is included as a converging blue-light input on COP1-SPA and is context only. No PANTHER family or PTN ids are asserted, because members are grounded directly as UniProt gene products. gocams/index.tsv has no production GO-CAM containing these genes. Falcon module deep research was not run; gene-level Falcon reports for SPA1 and PIF1 were generated and used as retrieval support.

6Nodes
5Parts
0Variant Sets
0Variants
11Annotons
6Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:phytochrome_photomorphogenesis deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

11 gene-function check(s) reflected in core functions · 0 conflict(s) · 0 evidence or coverage gap(s) (11 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
phyb_red_light_photoreceptor PHYB
UniProtKB:P14713
Gene 		red or far-red light photoreceptor activity
GO:0009883 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
phya_far_red_light_photoreceptor PHYA
UniProtKB:P14712
Gene 		far-red light photoreceptor activity
GO:0031516 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pif1_transcription_factor PIF1
UniProtKB:Q8GZM7
Gene 		DNA-binding transcription factor activity
GO:0003700 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pif3_transcription_factor PIF3
UniProtKB:O80536
Gene 		DNA-binding transcription factor activity
GO:0003700 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pif4_transcription_factor PIF4
UniProtKB:Q8W2F3
Gene 		DNA-binding transcription factor activity
GO:0003700 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pif1_cop1_cofactor PIF1
UniProtKB:Q8GZM7
Gene 		ubiquitin-protein transferase activator activity
GO:0097027 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
spa1_pif1_kinase SPA1
UniProtKB:Q9SYX2
Gene 		protein serine/threonine kinase activity
GO:0004674 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cop1_e3_ligase COP1
UniProtKB:P43254
Gene 		ubiquitin protein ligase activity
GO:0061630 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
spa1_cop1_activator SPA1
UniProtKB:Q9SYX2
Gene 		ubiquitin-protein transferase activator activity
GO:0097027 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
hy5_transcription_factor HY5
UniProtKB:O24646
Gene 		DNA-binding transcription factor activity
GO:0003700 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cry1_blue_light_photoreceptor CRY1
UniProtKB:Q43125
Gene 		blue light photoreceptor activity
GO:0009882 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).

Feedback loops (advisory, prose-driven: a regulator counts as "feedback" when its own description says so)

✓ every negative regulator described as feedback has an upstream edge closing the loop.

  • phytochrome_photoperception ⊣ pif_repressors [input]
    phytochrome_photoperception is a negative regulator with no upstream edge (not described as feedback)
  • cop1_spa_ligase ⊣ hy5_photomorphogenic_output [closed]
    cop1_spa_ligase is regulated by pif_repressors: feedback loop closed
  • cryptochrome_input ⊣ cop1_spa_ligase [input]
    cryptochrome_input is a negative regulator with no upstream edge (not described as feedback)

Gene-review completeness (9/9 grounded genes reviewed)

9 complete review(s) · 9 with deep research · 0 missing review · 0 reviewed but lacking deep research

Gene Review Complete Deep research
COP1 P43254 ✓ ✓ ✓
CRY1 Q43125 ✓ ✓ ✓
HY5 O24646 ✓ ✓ ✓
PHYA P14712 ✓ ✓ ✓
PHYB P14713 ✓ ✓ ✓
PIF1 Q8GZM7 ✓ ✓ ✓
PIF3 O80536 ✓ ✓ ✓
PIF4 Q8W2F3 ✓ ✓ ✓
SPA1 Q9SYX2 ✓ ✓ ✓

Details

Context
Arabidopsis thalianaNCBITaxon:3702
nucleusGO:0005634
Phytochrome control of photomorphogenesisSignaling Pathwayphytochrome_photomorphogenesis
red or far-red light signaling pathwayGO:0010017 photomorphogenesisGO:0009640
Context
Arabidopsis thalianaNCBITaxon:3702
nucleusGO:0005634

Connections

Pfr phytochromes bind PIFs and induce their phosphorylation and proteasomal degradation.
Pfr phyA and phyB bind SPA proteins and disrupt COP1-SPA, inactivating the ligase.
COP1-SPA ubiquitinates HY5 for degradation in darkness.
pif_repressors -> cop1_spa_ligase Positively Regulates
In darkness PIF1 enhances COP1 substrate recruitment and E3 activity.
cop1_spa_ligase -> pif_repressors Negatively Regulates
In light, CUL4-COP1-SPA ubiquitinates phosphorylated PIF1 for degradation, so the ligase degrades its own cofactor.
cryptochrome_input -> cop1_spa_ligase Negatively Regulates
Blue-light CRY1 binding to SPA1 suppresses COP1-SPA activity (context input).
Part 1: phytochrome photoperception
Phytochrome photoperception and nuclear photobody formationRegulatory Stepphytochrome_photoperception

Red light converts phyB, and far-red or very low fluence light converts phyA, to the active Pfr form. Pfr enters the nucleus (phyA through FHY1/FHL) and accumulates in nuclear bodies (photobodies), where it binds PIFs and SPA proteins.

Annotons

phyB red light photoreceptor
phyb_red_light_photoreceptor
Participant: Gene Product: PHYB
Gene Product:
PHYBUniProtKB:P14713

Function

red or far-red light photoreceptor activityGO:0009883

Processes

red or far-red light signaling pathwayGO:0010017

Locations

nuclear bodyGO:0016604

Dominant photoreceptor in continuous red light; Pfr phyB binds PIFs and SPA1, promoting PIF degradation and COP1-SPA1 dissociation.

PMID:25744387
Photoactivated phyB represses COP1-SPA1 association via red-light-dependent binding to SPA1.
the photoactivated phyB represses the association of SPA1 with COP1, which is mediated, at least in part, through red-light-dependent interaction of phyB with SPA1
phyA far-red light photoreceptor
phya_far_red_light_photoreceptor
Participant: Gene Product: PHYA
Gene Product:
PHYAUniProtKB:P14712

Function

far-red light photoreceptor activityGO:0031516

Processes

far-red light signaling pathwayGO:0010018

Locations

nuclear bodyGO:0016604

Type I photoreceptor for continuous far-red (high-irradiance) and very low fluence responses; Pfr phyA binds PIF1/PIF3 and SPA proteins and dominates early PIF1 degradation.

PMID:18539749
phyA dominates the initial light-induced degradation of PIF1.
phyA plays a dominant role in regulating the degradation of PIF1 following initial light exposure
Part 2: PIF growth-promoting transcription factors and their light-induced removal
PIF repressors of photomorphogenesis (degraded in response to phytochrome)Regulatory Steppif_repressors

PIF bHLH factors bind G-box elements and repress photomorphogenesis (and, for PIF1, germination and chlorophyll biosynthesis) in darkness. Binding of Pfr phytochrome triggers rapid PIF phosphorylation, ubiquitination and proteasomal degradation. For PIF1, SPA1 kinase activity in a phyB-PIF1-SPA1 complex and the CUL4-COP1-SPA ligase are required.

Annotons

PIF1 (PIL5) bHLH transcription factor
pif1_transcription_factor
Participant: Gene Product: PIF1
Gene Product:
PIF1UniProtKB:Q8GZM7

Function

DNA-binding transcription factor activityGO:0003700

Processes

negative regulation of photomorphogenesisGO:0010100 negative regulation of seed germinationGO:0010187

Locations

nucleusGO:0005634

Highest phytochrome-affinity PIF; degraded within minutes in red light; direct regulator of germination (GAI, RGA, SOM) and chlorophyll (PORC) genes.

PMID:18539749
PIF1 is phosphorylated, ubiquitinated and degraded within minutes in red light.
PIF1 is rapidly phosphorylated and ubiquitinated under red and far-red light before being degraded with a half-life of approximately 1 to 2 min under red light
PIF3 bHLH transcription factor
pif3_transcription_factor
Participant: Gene Product: PIF3
Gene Product:
PIF3UniProtKB:O80536

Function

DNA-binding transcription factor activityGO:0003700

Processes

red or far-red light signaling pathwayGO:0010017

Locations

nucleusGO:0005634

Founding PIF; binds Pfr phyA and phyB, is phosphorylated and degraded in light, and represses chlorophyll/photosynthesis genes in etiolated seedlings.

PMID:15155879
Red and far-red light induce rapid phytochrome-controlled degradation of PIF3.
red (R) and far-red light (FR) induce rapid degradation of the PIF3 protein
PIF4 bHLH transcription factor
pif4_transcription_factor
Participant: Gene Product: PIF4
Gene Product:
PIF4UniProtKB:Q8W2F3

Function

DNA-binding transcription factor activityGO:0003700

Processes

red or far-red light signaling pathwayGO:0010017

Locations

nucleusGO:0005634

Growth-promoting PIF that preferentially binds Pfr phyB and drives hypocotyl elongation genes; its temperature and hormone roles are outside this module.

PMID:12006496
PIF4 binds Pfr phyB selectively and acts negatively in phyB signaling.
PIF4 (phytochrome-interacting factor 4), which binds selectively to the biologically active Pfr form of phyB, but has little affinity for phyA
PIF1 as a cofactor enhancing COP1 E3 ligase activity
pif1_cop1_cofactor
Participant: Gene Product: PIF1
Gene Product:
PIF1UniProtKB:Q8GZM7

Function

ubiquitin-protein transferase activator activityGO:0097027

Processes

negative regulation of photomorphogenesisGO:0010100

Locations

nucleusGO:0005634

In darkness PIF1 complexes with COP1, SPA1 and HY5 and increases COP1 substrate recruitment, autoubiquitylation and HY5 transubiquitylation; this is the activity behind the PIF-to-ligase POSITIVELY_REGULATES connection.

PMID:24858936
PIF1 enhances COP1 substrate recruitment and E3 ligase activity in vitro.
PIF1 forms complexes with COP1, HY5, and SPA1 and enhances the substrate recruitment and autoubiquitylation and transubiquitylation activities of COP1
SPA1 kinase-like domain phosphorylating PIF1
spa1_pif1_kinase
Participant: Gene Product: SPA1
Gene Product:
SPA1UniProtKB:Q9SYX2

Function

protein serine/threonine kinase activityGO:0004674

Processes

red or far-red light signaling pathwayGO:0010017

Locations

nucleusGO:0005634

Reported Ser/Thr kinase activity of the SPA1 N-terminal domain that phosphorylates PIF1 in a phyB-enhanced complex, priming CUL4-COP1-SPA-mediated ubiquitination (evidence from one research group; see module notes).

PMID:31527679
SPA1 phosphorylates PIF1; phyB enhances PIF1 recruitment to SPA1.
SPA1 acts as a serine/threonine kinase and directly phosphorylates PIF1 in vitro and in vivo
Part 3: COP1-SPA E3 ubiquitin ligase
CUL4-DDB1-COP1-SPA E3 ubiquitin ligaseRegulatory Stepcop1_spa_ligase

COP1 is a RING E3 ubiquitin ligase. Bound through its coiled-coil to SPA proteins and associated with CUL4-DDB1, it ubiquitinates HY5 and other photomorphogenesis-promoting factors for proteasomal degradation in darkness. SPA1 stimulates COP1 E3 activity. Light-activated phytochromes and cryptochromes bind SPA proteins and disrupt the COP1-SPA interaction; light also triggers COP1 nuclear exclusion.

Annotons

COP1 RING E3 ubiquitin ligase
cop1_e3_ligase
Participant: Gene Product: COP1
Gene Product:
COP1UniProtKB:P43254

Function

ubiquitin protein ligase activityGO:0061630

Processes

negative regulation of photomorphogenesisGO:0010100

Locations

nucleusGO:0005634

Catalytic E3 that ubiquitinates HY5 (and HFR1, LAF1) in darkness.

PMID:14597662
COP1 ubiquitinates HY5 in vitro, and SPA1 alters this activity.
We further demonstrate the E3 ubiquitin ligase activity of COP1 on HY5 in vitro and the alteration of that activity by SPA1
SPA1 COP1-activating subunit
spa1_cop1_activator
Participant: Gene Product: SPA1
Gene Product:
SPA1UniProtKB:Q9SYX2

Function

ubiquitin-protein transferase activator activityGO:0097027

Processes

negative regulation of photomorphogenesisGO:0010100

Locations

nuclear bodyGO:0016604

Coiled-coil partner of COP1 that stimulates COP1 E3 activity; the target through which Pfr phyA/phyB (and CRY1/CRY2) inactivate the ligase.

PMID:12827204
SPA1 stimulates COP1 E3 activity toward LAF1.
SPA1 stimulates the E3 activity of residual nuclear COP1 to ubiquitinate LAF1
PMID:20061554
COP1-SPA complexes associate with CUL4-DDB1.
a series of CUL4-DDB1-COP1-SPA E3 ligase complexes may mediate the repression of photomorphogenesis
Part 4: photomorphogenic transcriptional output
HY5-driven photomorphogenic gene expressionRegulatory Stephy5_photomorphogenic_output

With COP1-SPA inactive, the bZIP transcription factor HY5 accumulates and binds light-responsive promoters to promote photomorphogenic gene expression. Together with the loss of PIF activity this produces de-etiolation.

Annotons

HY5 bZIP transcription factor
hy5_transcription_factor
Participant: Gene Product: HY5
Gene Product:
HY5UniProtKB:O24646

Function

DNA-binding transcription factor activityGO:0003700

Processes

photomorphogenesisGO:0009640

Locations

nucleusGO:0005634

Positive regulator of photomorphogenesis; COP1-SPA substrate stabilized in light and in cop1/spa/pif mutants.

PMID:24858936
HY5 is stabilized when COP1-SPA or PIFs are lost, and hy5 suppresses pifq.
the hy5 mutant suppresses the constitutive photomorphogenic phenotypes of the pifq mutant in the dark
Part 5: converging blue-light cryptochrome input (context)
Cryptochrome inhibition of COP1-SPA (context)Regulatory Stepcryptochrome_input

Context only. Photoexcited CRY1 binds SPA1 in blue light and suppresses the SPA1-COP1 interaction. This blue-light input converges on the same COP1-SPA node as the phytochromes but is not part of the red/far-red core.

Annotons

CRY1 blue light photoreceptor
cry1_blue_light_photoreceptor
Participant: Gene Product: CRY1
Gene Product:
CRY1UniProtKB:Q43125

Function

blue light photoreceptor activityGO:0009882

Blue-light receptor whose interaction with SPA1 suppresses COP1 activity.

PMID:21511871
CRY1-SPA1 interaction suppresses SPA1-COP1 interaction and HY5 degradation.
the CRY1-SPA1 interaction suppresses the SPA1-COP1 interaction and COP1-dependent degradation of the transcription factor HY5