Comparative analysis of the R1 late blight disease resistance gene cluster of hexaploid wild potato, Solanum demissum, reveals substantial variations between haplotypes

KUANG, H; MARANO, M. R; WIRTZ, U.; WEI, F.; LIU, J.; ET. AL.

San Diego, California

Congreso; XIII Conference - Plant and Animal Genome; 2005

Plant and Animal Genome

Several resistance genes, including R1 against Phytophthora infestans, were previously mapped to a resistance gene cluster (R1 cluster) on the superior arm of potato chromosome V. To better understand the organization and evolution of resistance (R-) genes and clusters, a physical map (~1 Mb) of the R1 cluster was constructed for each of the three haplotypes of allohexaploid wild potato Solanum demissum. A total of 691 Kb, 919 Kb and 441 Kb were sequenced for the three haplotypes, respectively. Three distinct gene families encoding nucleotide-binding-site (NBS) and Leucine-Rich-Repeat (LRR) domains were identified. One family is homologous to resistance gene R1 in potato, while the remaining two are homologous to Prf and Bs4 in tomato, respectively. The R1 homologues were grouped in two sub-clusters. The centromeric sub-cluster was sequenced across all three haplotypes and found to vary from ~5 Kb to 300 Kb. R1 was identified on haplotype A of this sub-cluster. The number of R1 homologues varied from one to 16 in the centromeric sub-clusters of the three haplotypes. Frequent sequence exchanges occurred between the R1 homologues at the centromeric sub-cluster and no allelic/orthologous relationships of R1 homologues were observed across the three haplotypes. In contrast to the dynamic R1 sub-cluster, flanking regions are highly conserved in the three haplotypes. Two Prf homologues are located centromeric to the R1 cluster, and are highly conserved in three haplotypes. At least one Bs4 homologue is located telomeric to the R1 cluster, coinciding with the mapped position of resistance gene Nb.