title: The E3 ubiquitin ligase HOS1 regulates low ambient temperature-responsive flowering in Arabidopsis thaliana.
abstract: Ubiquitin-dependent proteolysis regulates multiple aspects of plant growth and development, but little is known about its role in ambient temperature-responsive flowering. In addition to being regulated by daylength, the onset of flowering in many plants can also be delayed by low ambient temperatures. Here, we show that HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1), which encodes an E3 ubiquitin ligase, controls flowering time in response to ambient temperatures (16 and 23°C) and intermittent cold. hos1 mutants flowered early, and were insensitive to ambient temperature, but responded normally to vernalization and gibberellic acid. Genetic analyses suggested that this ambient temperature-insensitive flowering was independent of FLOWERING LOCUS C (FLC). Also, FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) expression was up-regulated in hos1 mutants at both temperatures. The ft tsf mutation almost completely suppressed the early flowering of hos1 mutants at different temperatures, suggesting that FT and TSF are downstream of HOS1 in the ambient temperature response. A lesion in CONSTANS (CO) did not affect the ambient temperature-insensitive flowering phenotype of hos1-3 mutants. In silico analysis showed that FVE was spatiotemporally co-expressed with HOS1. A HOS1-green fluorescent protein (GFP) fusion co-localized with FVE-GFP in the nucleus at both 16 and 23°C. HOS1 physically interacted with FVE and FLK in yeast two-hybrid and co-immunoprecipitation assays. Moreover, hos1 mutants were insensitive to intermittent cold. Collectively, our results suggest that HOS1 acts as a common regulator in the signaling pathways that control flowering time in response to low ambient temperature.
authors.affiliation: Creative Research Initiatives, Division of Life Sciences, Korea University, Seoul 136-701, Korea.
authors.forename: Jeong Hwan
authors.initials: JH
authors.lastname: Lee
authors.forename: Jae Joon
authors.initials: JJ
authors.lastname: Kim
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Hyun Jung
authors.initials: HJ
authors.lastname: Cho
authors.forename: Joonki
authors.initials: J
authors.lastname: Kim
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Ahn
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003080:Cold Temperature; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D035264:Flowers / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D026161:MADS Domain Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D049488:Phosphatidylethanolamine Binding Protein / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C418902:At5g10140 protein, Arabidopsis; C418905:FT protein, Arabidopsis; D005875:Gibberellins; C425768:HOS1 protein, Arabidopsis; D047908:Intracellular Signaling Peptides and Proteins; D026161:MADS Domain Proteins; C116635:MSI4 protein, Arabidopsis; D009687:Nuclear Proteins; D049488:Phosphatidylethanolamine Binding Protein; C500577:TSF protein, Arabidopsis; D014157:Transcription Factors; C007842:gibberellic acid