CBF2/DREB1C is a negative regulator ofCBF1/DREB1BandCBF3/DREB1Aexpression and plays a central role in stress tolerance inArabidopsis

Abstract
CBF/DREB1(C-repeat-binding factor/dehydration responsive element-binding factor 1) genes encode a small family of transcriptional activators that have been described as playing an important role in freezing tolerance and cold acclimation inArabidopsis. To specify this role, we used a reverse genetic approach and identified a mutant,cbf2, in which theCBF2/DREB1Cgene was disrupted. Here, we show thatcbf2plants have higher capacity to tolerate freezing than WT ones before and after cold acclimation and are more tolerant to dehydration and salt stress. All these phenotypes correlate with a stronger and more sustained expression of CBF/DREB1-regulated genes, which results from an increased expression ofCBF1/DREB1BandCBF3/DREB1Ain the mutant. In addition, we show that the expression ofCBF1/DREB1BandCBF3/DREB1Ain response to low temperature precedes that ofCBF2/DREB1C. These results indicate that CBF2/DREB1C negatively regulatesCBF1/DREB1BandCBF3/DREB1A, ensuring that their expression is transient and tightly controlled, which, in turn, guarantees the proper induction of downstream genes and the accurate development ofArabidopsistolerance to freezing and related stresses.

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