title: CBF gene copy number variation at Frost Resistance-2 is associated with levels of freezing tolerance in temperate-climate cereals.
abstract: Frost Resistance-1 (FR-1) and FR-2 are two loci affecting freezing tolerance and winter hardiness of the temperate-climate cereals. FR-1 is hypothesized to be due to the pleiotropic effects of VRN-1. FR-2 spans a cluster of C-Repeat Binding Factor (CBF) genes. These loci are genetically and functionally linked. Recent studies indicate CBF transcripts are downregulated by the VRN-1 encoded MADS-box protein or a factor in the VRN-1 pathway. Here, we report that barley genotypes 'Dicktoo' and 'Nure' carrying a vrn-H1 winter allele at VRN-H1 harbor increased copy numbers of CBF coding sequences relative to Vrn-H1 spring allele genotypes 'Morex' and 'Tremois'. Sequencing bacteriophage lambda genomic clones from these four genotypes alongside DNA blot hybridizations indicate approximately half of the eleven CBF orthologs at FR-H2 are duplicated in individual genomes. One of these duplications discriminates vrn-H1 genotypes from Vrn-H1 genotypes. The vrn-H1 winter allele genotypes harbor tandem segmental duplications through the CBF2A-CBF4B genomic region and maintain two distinct CBF2 paralogs, while the Vrn-H1 spring allele genotypes harbor single copies of CBF2 and CBF4. An additional CBF gene, CBF13, is a pseudogene interrupted by multiple non-sense codons in 'Tremois' whereas CBF13 is a complete uninterrupted coding sequence in 'Dicktoo' and 'Nure'. DNA blot hybridization with wheat DNAs reveals greater copy numbers of CBF14 also occurs in winter wheats than in spring wheats. These data indicate that variation in CBF gene copy numbers is widespread in the Triticeae and suggest selection for winter hardiness co-selects winter alleles at both VRN-1 and FR-2.
authors.affiliation: Department of Horticulture and Crop Science, The Ohio State University/Ohio Agricultural Research and Development Center, 1680 Madison Ave, Wooster, OH 44691, USA.
authors.forename: Andrea K
authors.initials: AK
authors.lastname: Knox
authors.forename: Taniya
authors.initials: T
authors.lastname: Dhillon
authors.forename: Hongmei
authors.initials: H
authors.lastname: Cheng
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tondelli
authors.forename: Nicola
authors.initials: N
authors.lastname: Pecchioni
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Stockinger
mesh_terms: D000483:Alleles; D002980:Climate; D003080:Cold Temperature; D018744:DNA, Plant / Q000235:genetics; D005615:Freezing; D018628:Gene Dosage; D017343:Genes, Plant; D001467:Hordeum / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics*; D056916:Segmental Duplications, Genomic
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins