Nup96 and HOS1 Are Mutually Stabilized and Gate CONSTANS Protein Level, Conferring Long-Day Photoperiodic Flowering Regulation in Arabidopsis

Plant Cell. 2020 Feb;32(2):374-391. doi: 10.1105/tpc.19.00661. Epub 2019 Dec 11.


The nuclear pore complex profoundly affects the timing of flowering; however, the underlying mechanisms are poorly understood. Here, we report that Nucleoporin96 (Nup96) acts as a negative regulator of long-day photoperiodic flowering in Arabidopsis (Arabidopsis thaliana). Through multiple approaches, we identified the E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (HOS1) and demonstrated its interaction in vivo with Nup96. Nup96 and HOS1 mainly localize and interact on the nuclear membrane. Loss of function of Nup96 leads to destruction of HOS1 proteins without a change in their mRNA abundance, which results in overaccumulation of the key activator of long-day photoperiodic flowering, CONSTANS (CO) proteins, as previously reported in hos1 mutants. Unexpectedly, mutation of HOS1 strikingly diminishes Nup96 protein level, suggesting that Nup96 and HOS1 are mutually stabilized and thus form a novel repressive module that regulates CO protein turnover. Therefore, the nup96 and hos1 single and nup96 hos1 double mutants have highly similar early-flowering phenotypes and overlapping transcriptome changes. Together, this study reveals a repression mechanism in which the Nup96-HOS1 repressive module gates the level of CO proteins and thereby prevents precocious flowering in long-day conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • DNA-Binding Proteins / metabolism
  • Flowers / genetics
  • Flowers / metabolism*
  • Gene Expression Regulation, Plant
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Mutation
  • Nuclear Envelope
  • Nuclear Pore Complex Proteins / genetics
  • Nuclear Pore Complex Proteins / metabolism*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Photoperiod*
  • Transcription Factors / metabolism
  • Transcriptome
  • Ubiquitin-Protein Ligases


  • Arabidopsis Proteins
  • CONSTANS protein, Arabidopsis
  • DNA-Binding Proteins
  • HOS1 protein, Arabidopsis
  • Intracellular Signaling Peptides and Proteins
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • Transcription Factors
  • nuclear pore complex protein 96
  • Ubiquitin-Protein Ligases