Plant, Animal & Microbe Genomes X Conference

January 12-16, 2002
Town & Country Convention Center
San Diego, CA

Poster: Gene Isolation
            

IDENTIFICATION OF HIGHLY UNSTABLE DISEASE RESISTANCE GENE LIKE SEQUENCES THAT CO-SEGREGATE WITH THE PHYTOPHTHORA RESISTANCE GENE, Rps4

¹ Deapartment of Agronomy, Iowa State University, Ames, Iowa, IA50011

A series of single dominant Rps genes confer resistance of soybean against root and stem rot disease caused by Phytophthora sojae. We have recently cloned NBS-like disease resistance gene sequences that mapped putatively to the Rps4 locus. Genetic linkage mapping using a set of SSR markers suggested that Rps4 mapped to the molecular linkage group G. A BAC library from the cultivar Williams 82 (containing the susceptible haplotype for rps4) was screened using NBS-like sequences. A BAC contig of about 200 kb was constructed for the region. We are in the process of developing a high-resolution molecular map for this region to determine if the NBS sequences are from the Rps4 locus. Southern blot analyses of F₁s between Williams (rps4rps4) x Haro4272 (Rps4Rps4) indicated that about 5% of the F₁s were rearranged for NBS sequence-specific HindIII restriction fragments. Rearrangements are characterized by deletions and appearances of new HindIII fragments. Analysis of the parents indicated that they were normal for HindIII-restriction patterns. Several types of rearranged F₁s were obtained; however, the pattern of rearrangements among F₁s obtained from a single cross was unique. We conclude from these data that these rearrangements were developed through an unusual recombination event just prior to differentiation of the whole flower, and may have implication in the evolution of resistance gene like sequences in soybean.