Submitted to: Biennial Conference on Molecular and Cellular Biology of the Soybean
Publication Type: Abstract Only
Publication Acceptance Date: 7/20/2008
Publication Date: N/A
Technical Abstract: Asian Soybean Rust (ASR) is caused by the fungus Phakospora pachyrhizi and is a threat to soybean production in many areas of the world including the United States. Thus far, only five sources of resistance have been identified (Rpp1, Rpp2, Rpp3, Rpp4, and Rpp5). Previous work by Silva et al (2008) mapped the Rpp4 locus to linkage group G of soybean. SSR marker Satt288, located within 2 cM of the Rpp4 locus, was used to screen the Iowa State University/USDA-ARS ‘Williams 82’ BAC library. Primers designed from BAC-end sequences and SSR Sat_143 were used to anchor and further expand the contig. BAC-end sequences and skim sequencing of selected BACs within the contig revealed a cluster of R genes. Shotgun sequencing of two identified BACs identified three R genes of the NBS-LRR class within the Rpp4 locus. TBLASTX (E<10E-4) searches against the recently released soybean genome (JGI; www.phytozome.net) identified only one Rpp4 candidate gene (RCG) homolog within the soybean genome. A duplicated genomic region syntenic to the Rpp4 locus was identified by additional BLASTN (E<10E-4) searches. Although gene content and order were conserved, no RCG homologs were present in the duplicated region region. The rarity of the RCG genes in the genome may correlate to the rarity of resistance to ASR. SSR markers have been developed within the RCG cluster to pinpoint the resistance gene and to aid in future breeding efforts. These new markers may also be used to test the RCGs as possible candidates for resistance to other pathogens.