HOS1 is an E3 ubiquitin-protein ligase that acts as a common regulator in the signalling pathways that control flowering time [, ]. It mediates ubiquitination and subsequent proteasomal degradation of the transcription factor ICE1 under cold treatment []. 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 []. Together with Nup96, HOS1 regulates CO protein turnover and thereby prevents precocious flowering in long-day conditions [].
