InterPro domain: IPR044718

HOS1 is an E3 ubiquitin-protein ligase that acts as a common regulator in the signalling pathways that control flowering time [ 1 , 2 ]. It mediates ubiquitination and subsequent proteasomal degradation of the transcription factor ICE1 under cold treatment [ 3 ]. In Arabidopsis, CONSTANS (CO) activates transcription of the floral integrators, FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) genes, which in turn govern the flowering time [ 4 ]. Together with Nup96, HOS1 regulates CO protein turnover and thereby prevents precocious flowering in long-day conditions [ 5 ].

1. The E3 ubiquitin ligase HOS1 regulates low ambient temperature-responsive flowering in Arabidopsis thaliana. Plant Cell Physiol 53, 1802-14
2. Nup96 and HOS1 Are Mutually Stabilized and Gate CONSTANS Protein Level, Conferring Long-Day Photoperiodic Flowering Regulation in Arabidopsis. Plant Cell 32, 374-391
3. The negative regulator of plant cold responses, HOS1, is a RING E3 ligase that mediates the ubiquitination and degradation of ICE1. Proc Natl Acad Sci U S A 103, 8281-6
4. CRISPR/Cas9-Mediated Knockout of HOS1 Reveals Its Role in the Regulation of Secondary Metabolism in Arabidopsis thaliana. Plants (Basel) 10