Comparative genome organization reveals a single copy of CBF in the freezing tolerant crucifer Thlaspi arvense.

The weedy crucifer species Thlaspi arvense has the ability to acclimate to lower temperatures than Arabidopsis thaliana and the related crop species, Brassica napus. As a step towards understanding the genetic basis for this enhanced low temperature response, we isolated and sequenced 8.7 kb of genomic DNA encompassing the T. arvense CBF locus. CBF is a transcription factor believed to play a pivotal role in the development of plant freezing tolerance. Sequence analysis revealed that T. arvense contains a single copy of CBF, whereas the co-linear, homologous region in A. thaliana contains three tandem copies. Genes that flank CBF in A. thaliana are also present in a co-linear arrangement in T. arvense. Comparative sequence alignment also revealed the presence of conserved sequence blocks between T. arvense and A. thaliana promoter regions. The expression of T. arvense CBF responds rapidly to low temperature but not demonstrably to ABA, dehydration or high salt, which is comparable to that of the A. thaliana CBF genes. Over-expression of Ta-CBF in transgenic A. thaliana resulted in the development of constitutive freezing tolerance, comparable to that of cold acclimated A. thaliana.