title: Genome analysis at different ploidy levels allows cloning of the powdery mildew resistance gene Pm3b from hexaploid wheat.
abstract: In wheat, race-specific resistance to the fungal pathogen powdery mildew (Blumeria graminis f. sp. tritici) is controlled by the Pm genes. There are 10 alleles conferring resistance at the Pm3 locus (Pm3a to Pm3j) on chromosome 1AS of hexaploid bread wheat (Triticum aestivum L.). The genome of hexaploid wheat has a size of 1.6 x 1010 bp and contains more than 80% of repetitive sequences, making positional cloning difficult. Here, we demonstrate that the combined analysis of genomes from wheat species with different ploidy levels can be exploited for positional cloning in bread wheat. We have mapped the Pm3b gene in hexaploid wheat to a genetic interval of 0.97 centimorgan (cM). The diploid T. monococcum and the tetraploid T. turgidum ssp. durum provided models for the A genome of hexaploid wheat and allowed to establish a physical contig spanning the Pm3 locus. Although the haplotypes at the Pm3 locus differed markedly between the three species, a large resistance gene-like family specific to wheat group 1 chromosomes was consistently found at the Pm3 locus. A candidate gene for Pm3b was identified using partial sequence conservation between resistant line Chul and T. monococcum cv. DV92. A susceptible Pm3b mutant, carrying a single-base pair deletion in the coding region of the candidate gene was isolated. When tested in a single cell transformation assay, the Pm3b candidate gene conferred race-specific resistance to powdery mildew. These results demonstrate that the candidate gene, a member of the coiled-coil nucleotide binding site leucine-rich repeat (NBS-LRR) type of disease resistance genes, is the Pm3b gene.
authors.affiliation: Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
authors.forename: Nabila
authors.initials: N
authors.lastname: Yahiaoui
authors.forename: Payorm
authors.initials: P
authors.lastname: Srichumpa
authors.forename: Robert
authors.initials: R
authors.lastname: Dudler
authors.forename: Beat
authors.initials: B
authors.lastname: Keller
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000254:growth & development*; D003001:Cloning, Molecular; D005720:Gamma Rays; D018745:Genome, Plant; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics; D007113:Immunity, Innate / Q000235:genetics; D000090263:Leucine-Rich Repeat Proteins; D008969:Molecular Sequence Data; D010802:Phylogeny; D020161:Physical Chromosome Mapping; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011003:Ploidies; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D014908:Triticum / Q000235:genetics* / Q000382:microbiology
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D000090263:Leucine-Rich Repeat Proteins; D010940:Plant Proteins; C486364:Pm3b protein, Triticum aestivum; D011506:Proteins