Phytochrome Signaling Mechanisms in Plant Systems

Phytochromes constitute a family of red- and far-red-light photoreceptors that orchestrate plant development by interconverting between an inactive Pr state and an active Pfr state upon photon absorption. The active Pfr form translocates to the nucleus, where it binds phytochrome-interacting factors (PIFs) and other partners to trigger conformational changes, phosphorylation events and ubiquitin-mediated proteolysis. These activities reshape transcriptional and post-transcriptional programmes controlling seed germination, hypocotyl elongation, shade avoidance, circadian entrainment and temperature responses. Central to this network are dedicated kinases that phosphorylate PIFs, E3 ubiquitin ligases that target them for 26S proteasome degradation, and photobodies—membraneless nuclear condensates that concentrate phytochromes with primary and secondary interactors into signalling hubs. Comparative analyses across land plants reveal a conserved core architecture alongside lineage-specific expansions, reflecting adaptation to diverse light regimes. Phytochromes also influence alternative promoter usage, mRNA splicing and translation, broadening the scope of light control beyond transcription. Recent advances in structural biology, live-cell imaging and synthetic photobiology have illuminated the conformational dynamics and molecular composition of phytochrome signalosomes. Elucidation of these mechanisms offers novel opportunities to engineer light responses for optimised crop yield, resource efficiency and resilience to changing climates.

Research from Nature Portfolio

Recent studies have defined the molecular composition of phyB photobodies, isolating approximately 1,500 phyB dimers alongside primary interactors that bind directly to phyB and secondary interactors that require co-expression of a primary partner for localisation. This work clarifies the organisation of subnuclear condensates as central signalling platforms. In parallel, a family of Photoregulatory Protein Kinases (PPK1–4) has been shown to engage photoactivated phytochromes in a light-dependent manner, directly catalysing the phosphorylation of PIF3. Loss of PPK activity impairs PIF3 phosphorylation and stabilisation, revealing these kinases as essential links between phytochrome activation and transcription factor turnover.

Phytochrome Signaling Mechanisms in Plant Systems publication trend

The graph below shows the total number of articles in phytochrome signaling mechanisms in plant systems across all publications each year (not limited to Nature Index journals).

Technical terms

Phytochrome: A bilin-binding photoreceptor switching between Pr and Pfr conformations to perceive red and far-red light.

Photobody: A membraneless nuclear condensate comprising phytochromes and their interactors that functions as a signalling hub.

Phytochrome-interacting factor (PIF): A basic helix–loop–helix transcription factor that binds active phytochromes and undergoes phosphorylation and degradation to regulate gene expression.

E3 ubiquitin ligase: An enzyme complex that tags target proteins with ubiquitin, marking them for proteasomal degradation.

Photoregulatory Protein Kinase (PPK): A nuclear kinase family that phosphorylates PIFs in response to phytochrome activation.

References

1. Phytochrome B photobodies are comprised of phytochrome B and its primary and secondary interacting proteins. Nature Communications (2023).
2. PPKs mediate direct signal transfer from phytochrome photoreceptors to transcription factor PIF3. Nature Communications (2017).
3. A Quartet of PIF bHLH Factors Provides a Transcriptionally Centered Signaling Hub That Regulates Seedling Morphogenesis through Differential Expression-Patterning of Shared Target Genes in Arabidopsis. PLOS Genetics (2013).
4. BLADE-ON-PETIOLE proteins act in an E3 ubiquitin ligase complex to regulate PHYTOCHROME INTERACTING FACTOR 4 abundance. eLife (2017).
5. Phytochrome diversity in green plants and the origin of canonical plant phytochromes. Nature Communications (2015).