The Arabidopsis HOS1 gene negatively regulates cold signal transduction and encodes a RING finger protein that displays cold-regulated nucleo-cytoplasmic partitioning

Low temperature is one of the most important environmental stimuli that con trol gene transcription programs and development in plants. In Arabidopsis thaliana, the HOS1 locus is a key negative regulator of low temperature-res ponsive gene transcription. The recessive hos1 mutation causes enhanced ind uction of the CBF transcription factors by low temperature as well as of th eir downstream cold-responsive genes. The hos1 mutant plants flower early, and this correlates with a low level of Flowering Locus C gene expression. The HOS1 gene was isolated through positional cloning. HOS1 encodes a novel protein with a RING finger motif near the amino terminus. HOS1 is ubiquito usly expressed in all plant tissues. HOS1-GFP translational fusion studies reveal that HOS1 protein resides in the cytoplasm at normal growth temperat ures. However, in response to low temperature treatments, HOS1 accumulates in the nucleus. Ectopic expression of HOS1 in wild-type plants causes cosup pression of HOS1 expression and mimics the hos1 mutant phenotypes.