Fine Mapping of a HvCBF gene cluster at Fr-H2, a QTL controlling frost resistance in barley.

Barley (Hordeum vulgare) is an economically important diploid model for the Triticeae. We developed a new resource for genetic analysis of winterhardiness-related traits, the \u2018Nure\u2019 (winter) x \u2018Tremois\u2019(spring) barley mapping population. Two low temperature QTLs were found to segregate on the long arm of chromosome 5H. A first distal QTL for low-temperature tolerance was identified at the VrnH1/Fr1 region (Fr-H1). A second proximal QTL for low-temperature tolerance was identified (Fr-H2) and it was coincident with the QTLs regulating the accumulation of two different and well characterized COR proteins (COR14b and TMC-Ap3). Six barley genes with the CBF transcription factor signature have been mapped in a single gene cluster in this region, and they represented the candidate genes underlying this Fr-H2. A population of 1,849 recombinant plants (F2 and BC1F2) was constructed and the resulting F3 families harboring none, both and only one QTL were phenotypically tested for validation of the two QT loci Fr-H1 and Fr-H2. The study was then focused towards the isolation of the determinant of Fr-H2, and a high-resolution genetic map of the HvCBF gene cluster was constructed by using the large segregating population. In this phase a shorter confidence interval (P=0.05) for the frost tolerance QTL effect was estimated. After fine mapping, recombinations between the HvCBF genes were observed. 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. Reciprocal QTL-NILs at Fr-H2 are also being devloped