Genomic and genetic analysis of the wheat race-specific yellow rust resistance gene Yr5

Abstract

Yellow rust, caused by the biotrophic fungus Puccinia striiformis f. sp. tritici (Pst), is a significant foliar disease of wheat (Triticum aestivum) and a major target for resistance breeding world-wide. The wheat race-specific yellow rust resistance (R)-gene Yr5 is a valuable source of resistance, still being effective against the pathogen in most wheat growing regions of the world. Through comparative genomic analyses, differential gene transcription and mutation studies, new genetic and genomic insights into this valuable resistance gene are provided. Co-locating DNA markers have been identified that have the potential to provide informative signatures for marker-based Yr5 introgression. Utilising the synteny between wheat and other cereal and grass species for which whole genome sequences are available, primer sets were developed for wheat sequences which co-segregate with Yr5 resistance, located on the long arm of chromosome 2B. Nucleotide and amino acid sequence searches aligned these wheat sequences with both the 5’ and 3’ ends of rice loci which showed significant homology to NB-LRR type R-genes. These rice loci were located on chromosomes 4 and 7, the rice chromosomes which are syntenic with the wheat group 2 chromosomes. Mutation analysis of the Yr5 locus indicated that loss of the gene had significant effects on the transcription of a number of genes involved in diverse cellular processes, this differential transcription being independent of the presence of the yellow rust pathogen Pst. Mutation analysis also identified loci, unlinked to Yr5, that were required for Yr5-mediated resistance.