A cluster of 11 CBF transcription factors is located at the frost tolerance locus Fr-A super(m)2 in Triticum monococcum

Due to the adverse effects of cold temperatures on winter wheat, frost tolerance is an important trait for breeding programs in regions with severe winters. Frost tolerance locus Fr-A super(m)2 was recently discovered in diploid wheat (Triticum monococcum L.). This locus was mapped as a QTL on chromosome 5A super(m) in the same region as a QTL for the level of transcription of the cold-regulated gene COR14b at 15 degree C. A CBF transcription factor was mapped in the center of these two overlapping QTLs. However, since the CBF gene family in wheat has numerous members, it was possible that multiple CBF genes were present at Fr-A super(m)2. To investigate this possibility we initiated a systematic characterization of the CBF family in T. monococcum. Here we report the molecular characterization of thirteen TmCBF genes. Nine of them were numbered according to the closest barley HvCBF gene, and the other four that have no clear barley orthologues were assigned numbers TmCBF15 to TmCBF18. TmCBF5 and TmCBF18 were mapped on T. monococcum chromosomes 7A super(m) and 6A super(m), respectively, and are thus not candidates for the Fr-A super(m)2 gene. The remaining eleven TmCBF genes are clustered at the Fr-A super(m)2 locus within five different Bacterial Artificial Chromosome (BAC) clones. These BACs were mapped using a high-density map and recombination events were found between most BACs. Lines carrying these recombination events will be useful to identify which of the CBF genes is responsible for the differences in frost tolerance between the T. monococcum parental lines at the Fr-A super(m)2 locus.