Cloning and mode of action of the major interspecific crossability locus (Kr1) in wheat

The genetic diversity available to breeders within wheat is very limited compared to that available within cultivated and wild relatives of wheat. However a number of barriers need to be overcome in order to have access to the full range of diversity within the wild relatives and to exploit this by introducing desirable genes from this exotic germplasm. The first barrier can be the failure of pollen from wild species to fertilise the wheat ovary. Although wheat can be crossed with a wide range of related species, most adapted wheat varieties are incompatible because of the failure of pollen to fertilize the ovary, thus greatly restricting the germplasm that can be used for alien introgression in wheat breeding. The biological basis for the failure of pollen from wild relatives to penetrate the wheat style and ovary remains to be elucidated. This present proposal addresses this issue. This will open up a new area of biology for cereals and grasses

Interspecific hybrids are used by breeders to introduce desirable genes from exotic germplasm into wheat. However the presence of several dominant genes, particularly the homoeologous series of Kr genes on the homoeologous group 5 chromosomes prevents this process by inhibiting pollen tube grown, thus stopping them from fertilizing the wheat ovary . The gene of largest effect, Kr1 on chromosome 5B, inhibits the ability to make crosses with most related species, for example rye and Hordeum bulbosum. By exploiting variability in crossability from the presence of the dominant (non-crossable) allele in the wheat variety Hobbit and the recessive (crossable) allele in the variety Chinese Spring (CS), the Kr1 gene has been mapped to the long arm of 5B. By creating single chromosome substitution lines (Hobbit CS5B) in which the Chinese Spring 5B chromosome had been substituted for the Hobbit 5B chromosome, the Kr1 gene can be further mapped.These lines will be scored for their ability to set seed when crossed with Petkus rye and tetraploid H bulbosum and screened with 5B specific molecular markers for whether the recombinant chromosomes carry the Hobbit or Chinese Spring alleles. Thus the Kr1 gene can be fine mapped on a molecular marker based map of chromosome 5B. By exploiting information from Kr1 equivalent regions in rice and Brachypodium, the Kr1 region in wheat can be BAC contiged and then sequenced. Annotation of the sequence will yield potential genes from which a candidate gene for Kr1 can be revealed by further fine mapping.