Arabidopsis FHY1 and FHY1-LIKE Are Not Required for Phytochrome A Signal Transduction in the Nucleus

Plant Commun. 2019 Nov 9;1(2):100007. doi: 10.1016/j.xplc.2019.100007. eCollection 2020 Mar 9.


Photoreceptors of the phytochrome family control a multitude of responses in plants. Phytochrome A (phyA) is essential for far-red light perception, which is important for germination and seedling establishment in strong canopy shade. Translocation of phyA from the cytosol into nucleus is a key step in far-red light signaling and requires FAR-RED ELONGATED HYPOCOTYL 1 (FHY1) and FHY1-LIKE (FHL). FHY1/FHL bind to phyA downstream signaling components. Therefore, it has been suggested that FHY1/FHL also have a function in assembling phyA transcription factor complexes in the nucleus. Yet, in this study, we show that constitutively nuclear-localized phyA is active in the absence of FHY1 and FHL. Furthermore, an artificial FHY1, consisting of an SV40 NLS, a phyA binding site, and a YFP tag as spacer between them, complements the fhy1-3 fhl-1 double mutant. These findings show that FHY1 and FHL are not required for phyA downstream signaling in the nucleus. However, we found that lines expressing phyA-NLS-YFP are hypersensitive to red and far-red light and that slightly increased levels of constitutively nuclear-localized phyA result in photomorphogenic development in the dark. Thus, restricting phyA to the cytosol and inducing nuclear transport in light by interaction with FHY1/FHL might be important to suppress photomorphogenesis in the dark.

Keywords: FHL; FHY1; far-red light; nuclear transport; phyA; phytochrome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / cytology
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Bacterial Proteins / genetics
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Gene Expression Regulation, Plant
  • Light
  • Luminescent Proteins / genetics
  • Mutation
  • Phytochrome / genetics
  • Phytochrome / metabolism*
  • Phytochrome A / genetics
  • Phytochrome A / metabolism*
  • Plants, Genetically Modified
  • Signal Transduction
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Arabidopsis Proteins
  • Bacterial Proteins
  • FHL protein, Arabidopsis
  • FHY1 protein, Arabidopsis
  • Luminescent Proteins
  • PHYA protein, Arabidopsis
  • Phytochrome A
  • Transcription Factors
  • yellow fluorescent protein, Bacteria
  • Phytochrome