<b>Low temperature regulation of the</b><i><b>Arabidopsis</b></i><b>CBF family of AP2 transcriptional activators as an early step in cold‐induced</b><i><b>COR</b></i><b>gene expression</b>

TLDR

Cold‑induced expression of Arabidopsis COR genes is mediated by the CRT/DRE DNA regulatory element. The study aims to characterize the CBF1–3 family and propose that their early induction drives low‑temperature activation of CRT/DRE‑containing COR genes. Genetic mapping and sequencing located the CBF1–3 genes as a direct repeat on chromosome 4 near markers PG11 and m600, and the authors propose that their rapid induction initiates a low‑temperature signalling cascade activating CRT/DRE‑containing COR genes. CBF1 overexpression triggers COR gene expression and enhances freezing tolerance, while CBF2 and CBF3 also activate CRT/DRE reporters; all three genes are rapidly induced by cold (within 15 min) and mechanical stress, with COR transcripts rising after ~2 h, and their promoters lack CRT motifs, suggesting the CBF family is not autoregulated.

Abstract

Summary 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 temperaturestimulated signalling cascade in which CBF gene induction is an early event.