Abstract
Low temperature is one of the most important environmental stimuli that control gene transcription programs and development in plants. In
Arabidopsis thaliana
, the
HOS1
locus is a key negative regulator of low temperature-responsive gene transcription. The recessive
hos1
mutation causes enhanced induction of the
CBF
transcription factors by low temperature as well as of their 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 ubiquitously expressed in all plant tissues. HOS1–GFP translational fusion studies reveal that HOS1 protein resides in the cytoplasm at normal growth temperatures. However, in response to low temperature treatments, HOS1 accumulates in the nucleus. Ectopic expression of
HOS1
in wild-type plants causes cosuppression of
HOS1
expression and mimics the
hos1
mutant phenotypes.