Rpp1 encodes a ULP-NBS-LRR protein that controls immunity to Phakopsora pachyrhizi in soybean
K. PEDLEY (1), A. Pandey (2), A. Ruck (1), S. Whitham (3), M. Graham (4) (1) Foreign Disease-Weed Science Research Unit, United States Department of Agriculture-Agricultural Research Service, U.S.A.; (2) National Agri-Food Biotechnology Institute, India; (3) Department of Plant Pathology and Microbiology, Iowa State University, U.S.A.; (4) Corn Insects and Crop Genetics Research Unit, United States Department of Agriculture-Agricultural Research Service, U.S.A.

Phakopsora pachyrhizi is the causal agent of Asian soybean rust. Susceptible soybean plants infected by virulent isolates of P. pachyrhizi are characterized by tan-colored lesions and erumpent uredinia on the leaf surface. Germplasm screening and genetic analyses have led to the identification of six loci, Rpp1 – Rpp6, that provide varying degrees of resistance to P. pachyrhizi (Rpp). Two genes, Rpp1 and Rpp1b, map to the Rpp1 locus. Rpp1 is unique among the Rpp genes in that it confers an immune response (IR) to avirulent P. pachyrhizi isolates. The IR is characterized by a lack of visible symptoms, whereas resistance provided by Rpp1b – Rpp6 results in red-brown foliar lesions. Rpp1 has been mapped to a region spanning approximately 150 Kb on chromosome 18 between markers Sct_187 and Sat_064. To identify Rpp1 we constructed a bacterial artificial chromosome (BAC) library from the Rpp1-containing soybean accession PI 200492. Sequencing of a single 324 Kb contig spanning the Rpp1 locus identified three homologous nucleotide binding site-leucine rich repeat (NBS-LRR) candidate resistance genes between Sct_187 and Sat_064. These genes are unusual in that they are predicted to encode an N-terminal ubiquitin-like protease (ULP) domain. Silencing of the Rpp1 candidate genes abrogated the immune response in PI 200492. These data indicate that Rpp1 is a novel ULP-NBS-LRR protein and suggest that desumoylation of one or more host proteins may play a role in Rpp1-mediated resistance.    

Abstract Number: P17-582
Session Type: Poster