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6

Microarray analysis of Rpp3-mediated resistance to soybean rust infection

Presenter: K. T. Schneider

All authors and affiliations: K. T. SCHNEIDER (1), M. van de Mortel (2), D. Nettleton (3), R. D. Frederick (1), T. J. Baum (2), and S. A. Whitham (2). (1) Foreign Disease-Weed Science Research Unit, USDA-ARS, Fort Detrick, MD 21702; (2) Department of Plant Pathology, Iowa State University, Ames, IA 50011; and (3) Department of Statistics, Iowa State University, Ames, IA

Phakopsora pachyrhizi, the causative agent of Asian soybean rust, is endemic in Asia and South America and was first observed in the United States in 2004. Commercially available U.S. soybean cultivars do not harbor any known rust resistance genes. Four independent rust resistance genes (Rpp1-Rpp4) have been described from noncommercial soybean accessions and confer phenotypes that range from immune (no visible symptoms) through resistant (reddish brown lesions combined with reduced sporulation) to fully susceptible (tan lesions and heavy sporulation), depending on the genotype of both the host plant and rust isolate studied. Gene expression profiling was used to identify and understand the soybean genes that are expressed in the Rpp3 resistant reaction. Soybean plants carrying the Rpp3 resistance gene were sampled at six time points after inoculation with specific isolates of soybean rust: 12, 24, 72, 144, 216, and 288 h. RNA was extracted from resistant and susceptible interactions at each time point, and gene expression was monitored using the Affymetrix Soybean Genome Array. Soybean genes that are differentially regulated following rust infection will be identified by mixed model analysis, and q values will be used to set a false discovery rate. Rust-responsive genes will be compared to known resistance pathways in other plant-microbe interactions with the goal of identifying signaling networks important for resistance to soybean rust. A comparison between rust-responsive genes in Rpp3-mediated resistance and genes identified in the Rpp1-immune reaction will serve as the basis for future investigations.

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