title: Resolving the aphid resistance locus Sd-1 on a BAC contig within a sub-telomeric region of Malus linkage group 7.
abstract: Aphids cause serious physical and economic damage to most major crops throughout the world, and there is a pressing requirement to isolate genes conferring aphid resistance. The Sd-1 locus in Malus spp. (apple) confers resistance against the rosy leaf-curling aphid (Dysaphis devecta Wlk.), and was recently positioned within a 1.3-cM region on linkage group 7, flanked by molecular markers. These markers were used as a basis for development of a BAC contig spanning the locus, together with adapter-mediated amplification of flanking sequences to obtain BAC insert-end sequences, and fingerprinting of BAC clones. Approximately 800 kb of the Sd-1 genomic region was covered by 19 overlapping BACs, with an average insert size of 75-150 kb. The physical-genetic distance ratio was estimated at 460 kb/cM, although the distribution of recombination events was irregular with respect to estimated physical distance. Recombinant analysis and development of new markers allowed Sd-1 to be positioned within an interval of approximately 180 kb located on either of two overlapping BACs. From one of these, an insert end sequence showed a significant degree of similarity to nucleotide binding site-leucine rich repeat (NBS-LRR) resistance genes. Fluorescent in situ hybridization (FISH) of BAC clones within the contig enabled positioning and orientation of the locus within a euchromatic region, very close to the telomere of linkage group 7.
authors.affiliation: Comparative Genomics and Genetics Group, HRI, Wellesbourne, Warwick, UK.
authors.forename: Volkan
authors.initials: V
authors.lastname: Cevik
authors.forename: Graham J
authors.initials: GJ
authors.lastname: King
mesh_terms: D000818:Animals; D001042:Aphids / Q000472:pathogenicity*; D001483:Base Sequence; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D032461:Chromosomes, Plant / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D017343:Genes, Plant; D008040:Genetic Linkage; D005819:Genetic Markers; D017404:In Situ Hybridization, Fluorescence; D027845:Malus / Q000235:genetics* / Q000469:parasitology*; D010935:Plant Diseases / Q000235:genetics / Q000469:parasitology; D016615:Telomere / Q000235:genetics
chemical_list: D017931:DNA Primers; D005819:Genetic Markers