Physical Mapping in a Triplicated Genome: Mapping the Downy Mildew Resistance LocusPp523inBrassica oleraceaL.

Abstract

We describe the construction of a BAC contig and identification of a minimal tiling path that encompass the dominant and monogenically inherited downy mildew resistance locus Pp523 of Brassica oleracea L. The selection of BAC clones for construction of the physical map was carried out by screening gridded BAC libraries with DNA overgo probes derived from both genetically mapped DNA markers flanking the locus of interest and BAC-end sequences that align to Arabidopsis thaliana sequences within the previously identified syntenic region. The selected BAC clones consistently mapped to three different genomic regions of B. oleracea. Although 83 BAC clones were accurately mapped within a ∼4.6 cM region surrounding the downy mildew resistance locus Pp523, a subset of 33 BAC clones mapped to another region on chromosome C8 that was ∼60 cM away from the resistance gene, and a subset of 63 BAC clones mapped to chromosome C5. These results reflect the triplication of the Brassica genomes since their divergence from a common ancestor shared with A. thaliana, and they are consonant with recent analyses of the C genome of Brassica napus. The assembly of a minimal tiling path constituted by 13 (BoT01) BAC clones that span the Pp523 locus sets the stage for map-based cloning of this resistance gene.

Comparison of Positions of QTLs Conferring Resistance to <i>Xanthomonas campestris</i> pv. <i>campestris</i> in <i>Brassica oleracea</i>

“…The upper part of C5, one of middle part of C8 and the distal end of C8 shared conserved regions with Arabidopsis thaliana chromosome 1 [37,38]. In addition, it is known that the large conserved regions are duplicated in C5 and C8 [38,39]. This indicates that XccBo(Reiho)1 on C5 and XccBo(Reiho)2 on C8 might be homologous loci.…”

Molecular-genetic marking of Brassica L. species for resistance against various pathogens: achievements and prospects

“…On the basis of the OPJ19 550 and OPR15 920 marker sequences linked with Pp523, probes (BoT01 and BoCig) were developed for screening genomic libraries of B. oleracea, with isolation of sites containing sequences complementary to the probes. DNA fragments in the isolated BAC clones were shown to be located in three different parts of the genome of B. oleracea: 83 clones were mapped to chromosome С08 near Pp523, 33 clones also to chromosome С08 at a distance of 60 cM from the resistance gene, and 63 more to chromosome С05 (Carlier et al, 2011). The presence of such triplication supports the hypothesis concerning the existence of Brassica's hexaploid ancestor some 14-24 million years ago and the formation of the B. oleracea genome by rearrangements and translocations (Carlier et al, 2011).…”

Current Status and Challenges in Identifying Disease Resistance Genes in Brassica napus

“…- B. oleracea (BAC libraries BoT01 and BoCig): Single dominant locus Pp523 on chromosome C8 and C5 (Carlier et al, 2011 )…”