Dawn and photoperiod sensing by phytochrome A

Daniel D Seaton, Gabriela Toledo-Ortiz, Ashwin Ganpudi, Akane Kubota, Takato Imaizumi, Karen J Halliday

Research output: Contribution to journalArticlepeer-review


In plants, light receptors play a pivotal role in photoperiod sensing, enabling them to track seasonal progression. Photoperiod sensing arises from an interaction between the plant's endogenous circadian oscillator and external light cues. Here, we characterize the role of phytochrome A (phyA) in photoperiod sensing. Our metaanalysis of functional genomic datasets identified phyA as a principal regulator of morning-activated genes, specifically in short photoperiods. We demonstrate that PHYA expression is under the direct control of the PHYTOCHROME INTERACTING FACTOR transcription factors, PIF4 and PIF5. As a result, phyA protein accumulates during the night, especially in short photoperiods. At dawn, phyA activation by light results in a burst of gene expression, with consequences for physiological processes such as anthocyanin accumulation. The combination of complex regulation of PHYA transcript and the unique molecular properties of phyA protein make this pathway a sensitive detector of both dawn and photoperiod.

Original languageEnglish
Pages (from-to)10523-10528
Number of pages6
JournalProceedings of the National Academy of Sciences (PNAS)
Issue number41
Early online date25 Sep 2018
Publication statusPublished - 9 Oct 2018


  • Arabidopsis
  • circadian rhythms
  • photoperiodism
  • phytochrome
  • systems biology


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