Copy number variation of barley CBF genes at Frost Resistance-H2 is associated with levels of freezing tolerance
Lathrop, Bonnie A.
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Following barley‟s domestication in the Fertile Crescent, genes controlling freezing tolerance, winter hardiness and vernalization may have incurred alterations. Freezing tolerance allows for plant survival over winter and freezing temperatures by induced physiological cold acclimation. Vernalization, or a period of prolonged cold temperature exposure, is required in many Triticeae species in order to progress from a vegetative growth stage to a reproductive flowering stage. Both winter and spring type alleles are found at the locus affecting vernalization requirement, named VRN-1. Frost-Resistance 1 (FR-1) and Frost-Resistance 2 (FR-2) are two loci that affect freezing tolerance and winter hardiness. Fr-1 is thought to be due to pathways activated by VRN-1 that alter a plant‟s ability to survive freezing temperatures. FR-2 lies with a cluster of C-Repeat Binding Factor (CBF) genes which code for numerous binding factors of downstream Cold Regulated (COR) genes which in turn affect pathways for freezing tolerance and cold acclimation. CBF gene expression has been found to vary between winter and spring varieties of wheat and barley; this distinction has been attributed to copy number variation, a genomic structural variant. This experiment sought to characterize variation in CBF2 expression between winter and spring genotypes in wild and semi-wild landrace genotypes of barley through DNA hybridization. We expected winter phenotyped wild and landrace barleys to have CBF2 copy numbers similar to cultivated winter hardy barley. Though no quantitative analysis could be completed, two CBF2 paralogs were present in many barley genotypes and provided interesting insights. Further analysis is necessary to reach firm conclusions surrounding copy number variation of CBFs and freezing tolerance levels in tested winter and spring barley types.