Three grape CBF/DREB1 genes respond to low temperature, drought and abscisic acid.

The C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding protein 1 (CBF/ DREB1) transcription factors control an important pathway for increased freezing and drought tolerance in plants. Three CBF/DREB1-like genes, CBF 1-3, were isolated from both freezing-tolerant wild grape (Vitis riparia) and freezing-sensitive cultivated grape (Vitis vinifera). The deduced proteins in V. riparia are 63-70% identical to each other and 96-98% identical to the corresponding proteins in V. vinifera. All Vitis CBF proteins are 42-51% identical to AtCBF1 and contain CBF-specific amino acid motifs, supporting their identification as CBF proteins. Grape CBF sequences are unique in that they contain 20-29 additional amino acids and three serine stretches. Agro-infiltration experiments revealed that VrCBF1b localizes to the nucleus. VrCBF1a, VrCBF1b and VvCBF1 activated a green fluorescent protein (GFP) or glucuronidase (GUS) reporter gene behind CRT-containing promoters. Expression of the endogenous CBF genes was low at ambient temperature and enhanced upon low temperature (4 degrees C) treatment, first for CBF1, followed by CBF2, and about 2 d later by CBF3. No obvious significant difference was observed between V. riparia and V. vinifera genes. The expression levels of all three CBF genes were higher in young tissues than in older tissues. CBF1, 2 and 3 transcripts also accumulated in response to drought and exogenous abscisic acid (ABA) treatment, indicating that grape contains unique CBF genes.