Molecular Characterization Of The Barley Fr-H2 QT Locus

Frost resistance-H2 is major quantitative trait locus that, in combination with VRN-H1/Fr-H1, affects freezing tolerance of barley. Mapping coincident with Fr-H2 are QTLs regulating COR proteins accumulation and a cluster of more than 14 genes encoding CBF transcription factors \u2013 at present the best candidates to explain the effects given by the locus. Expression analyses, conducted on a \u2018Nure\u2019 x \u2018Tremois\u2019 barley mapping population segregating for VRN-H1/Fr-H1 and Fr-H2, revealed that transcript levels of all cold-induced CBF genes at Fr-H2 were significantly higher in recombinants harboring the vrn-H1 winter allele than in recombinants harboring the Vrn-H1 spring allele. Also, steady-state HvCBF2 and HvCBF4 levels were significantly higher in recombinants harboring the Nure allele at Fr-H2. In a positional cloning effort, a large mapping population consisting of more than 3,698 meiotic events was used to fine map Fr-H2. Recombinants between 12 CBF genes under Fr-H2 have been identified in a total genetic distance of 0.81 cM. The few recombinants between the different HvCBF sub-clusters were chosen and taken to homozygosity in order to separate the effects of the single HvCBF genes. At the same time, a PCR-based screening strategy of the genomic BAC library of cv \u2018Morex\u2019 was undertaken, and selected clones assembled into contigs through high information content fingerprinting (HICF). BAC-end sequencing is being used to close remaining gaps and to create anchor points between the genetic and physical maps of the region. Alignment of the genetically colinear region of \u2018Nure\u2019 against \u2018Tremois\u2019, alongside \u2018Dicktoo\u2019 and \u2018Morex\u2019, revealed several key molecular differences that we hypothesize accounts for the nature of Fr-H2. The likely scenario is that both a \u2018structural\u2019 and a \u2018regulatory\u2019 component act together to enhance the tolerance. The first component could be likely due to either allelic or number variation of HvCBF genes at Fr-H2 where \u201cmore\u201d CBFs could be better, while the second one would be due to the winter allele of VRN-H1/Fr-H1