Light-quality regulation of freezing tolerance in Arabidopsis thaliana.

To acquire freezing tolerance, higher plants require a period of low temperature (usually <4 degrees C) termed cold acclimation. Upon transfer of plants to low temperature, increased expression of the CRT/DRE binding factor (CBF) family of transcriptional activators leads to the upregulation of genes containing a C-repeat/drought-responsive (CRT/DRE) promoter element and metabolic changes that enhance tolerance to subzero temperatures. Here, we show that a low red to far-red ratio (R/FR) light signal increases CBF gene expression in Arabidopsis thaliana in a manner dependent on the circadian clock. This light quality-dependent increase in CBF expression is sufficient to confer freezing tolerance at temperatures higher than those required for cold acclimation. Furthermore, the use of light-quality signals to stimulate CBF expression has revealed ambient temperature-dependent coupling of CBF transcription factors to downstream COLD REGULATED (COR) genes, providing evidence for a second temperature-regulated step in this pathway.