The obligate biotrophic fungus Phakopsora pachyrhizi Syd. & P. Syd. , the causal agent of soybean rust, is among the most formidable pathogens of soybean (Glycine max L. Merr. ). The pathogen is now established in all major soybean growing areas of the world and presents a significant impediment to global soybean production. Most soybean germplasm is susceptible, enabling the fungus to penetrate and colonize the leaf tissue, causing tan-colored necrotic lesions to form at the site of infection. Severe infection reduces photosynthesis and causes premature defoliation, which ultimately decreases crop yield and seed quality. Eight genetic loci, Rpp1/Rpp1b to Rpp7 and Rpp6907, that confer race-specific resistance to P. pachyrhizi (Rpp) have been identified. Rpp2 was identified and characterized in the soybean accession PI 230970 and fine-mapped to a 188. 1 kb interval on chromosome 16, a region predicted to contain several toll/interleukin-1 receptor nucleotide-binding leucine-rich repeat (TIR-NLR) genes. To identify Rpp2, we constructed a bacterial artificial chromosome (BAC) library from the resistant soybean accession PI 230970. Sequencing BACs that span the Rpp2 locus identified fourteen candidate genes with homology to the TIR-NLR family of resistance genes with integrated winged-helix (WH) domains. Of these, seven are predicted to encode full-length R proteins. Co-silencing the Rpp2 candidate genes compromised resistance in soybean accession PI 230970. Gene expression analysis suggests that a single gene, Rpp2C7PI, which shares greatest homology to Rpp2C6Wms82 (Glyma. 16G136600) in the Williams 82 reference genome, is responsible for Rpp2-mediated resistance.
Holan et al. (Thu,) studied this question.