ABSTRACT
Many plants, including Arabidopsis, show increased resistance to freezing after they have been exposed to low nonfreezing temperatures. This response, termed cold acclimation, is associated with the induction of COR (cold-regulated) genes mediated by the C-repeat/drought-responsive element (CRT/DRE) DNA regulatory element. Increased expression of Arabidopsis CBF1, a transcriptional activator that binds to the CRT/DRE sequence, induced COR gene expression and increased the freezing tolerance of nonacclimated Arabidopsis plants. We conclude that CBF1 is a likely regulator of the cold acclimation response, controlling the level of COR gene expression, which in turn promotes tolerance to freezing.
Subject(s)
Arabidopsis Proteins , Arabidopsis/genetics , DNA-Binding Proteins/genetics , Freezing , Gene Expression Regulation, Plant , Genes, Plant , Plant Proteins/genetics , Trans-Activators/genetics , Acclimatization , Arabidopsis/physiology , Cold Temperature , DNA-Binding Proteins/metabolism , Gene Transfer Techniques , Plant Leaves/physiology , Plant Proteins/metabolism , Plants, Genetically Modified , Promoter Regions, Genetic , Regulon , Trans-Activators/metabolismABSTRACT
Cold-induced expression of the Arabidopsis COR (cold-regulated) genes is mediated by a DNA regulatory element termed the CRT (C-repeat)/DRE (dehydration-responsive element). Recently, we identified a transcriptional activator, CBF1, that binds to the CRT/DRE and demonstrated that its overexpression in transgenic Arabidopsis plants at non-acclimating temperatures induces COR gene expression and increases plant freezing tolerance. Here we report that CBF1 belongs to a small family of closely related proteins which includes CBF2 and CBF3. DNA sequencing of an 8.7 kb region of the Arabidopsis genome along with genetic mapping experiments indicated that the three CBF genes are organized in direct repeat on chromosome 4 at 72.8 cM, closely linked to molecular markers PG11 and m600. Like CBF1, both CBF2 and CBF3 activated expression of reporter genes in yeast that contained the CRT/DRE as an upstream activator sequence. The transcript levels for all three CBF genes increased within 15 min of transferring plants to low temperature, followed by accumulation of COR gene transcripts at about 2 h. CBF transcripts also accumulated rapidly in response to mechanical agitation. The promoter regions of the CBF genes do not contain the CRT sequence, CCGAC, and overexpression of CBF1 did not have a detectable effect on CBF3 transcript levels, suggesting that the CBF gene family is not subject to autoregulation. We propose that cold-induced expression of CRT/DRE-containing COR genes involves a low temperature-stimulated signalling cascade in which CBF gene induction is an early event.