Using barley genomic resources for positional cloning of QTL in bread wheat

Progress in positional cloning of QTL had been slow in wheat due to the size (16,000 Mbp) and the polyploidy nature of its genome (AABBDD, 2n = 6x = 42). Most pathways and candidates genes are unknown and physical maps are only available for some chromosomes. Rice and brachypodium are often used as reference genomes for finding new markers in regions of interest in wheat using the syntenic relationship existing between grasses. However progress in generating high-throughput markers and BAC sequencing of wheat showed major differences in synteny that limit the use of distant species such as rice and brachypodium. Because they share a common Triticeae ancestor, barley is regarded as a model diploid species for wheat. Its seven pairs of chromosomes (HH, 2n = 2x = 14) correspond to the seven groups of homoeologous chromosomes in wheat. Comparative genomics has revealed high co-linearity of genes and molecular markers between wheat and barley genomes. Great genomic resources, particularly a whole genome physical map and BAC sequencing, are being available in barley. We used barley resources to identify a functional cluster of genes underlying a QTL controlling fructan content in wheat grain. Fructans are soluble carbohydrates with health benefits and possible roles in plant adaptation. Fructan biosynthetic genes were isolated using comparative genomics and physical mapping followed by BAC sequencing in barley. Similar strategy is being used for positional cloning of QTL improving yield under drought in wheat.