ARS | Publication request: Targeted Sequencing and Analyses of the Rpp4 Asian Soybean Rust Resistance Locus in Soybean

Submitted to: Biennial Conference on Molecular and Cellular Biology of the Soybean
Publication Type: Abstract Only
Publication Acceptance Date: July 20, 2008
Publication Date: N/A

Technical Abstract: Asian Soybean Rust (ASR) is a formidable threat to soybean production in many areas of the world and has recently made its way to 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. Skim sequencing of selected BACs within the contig revealed a cluster of disease resistance genes that had not been previously identified in soybean. 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. Additional BLASTN (E<10E-4) searches were used to identify a duplicated region syntenic to the Rpp4 locus. While gene content and order were conserved in this region, no RCG homologs were present. 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.