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5

Expression analysis of the Rpp1-mediated immune reaction to Phakopsora pachyrhizi using the Affymetrix Soybean Genome Array

Presenter: K. T. Schneider

All authors and affiliations: K. T. SCHNEIDER (1), J. J. Choi (1), N. L. Lum (2), D. J. Munroe (2), and R. D. Frederick (1). (1) Foreign Disease-Weed Science Research Unit, USDA-ARS, Fort Detrick, MD 21702; and (2) Laboratory of Molecular Technology, SAIC-Frederick, Inc., NCI-Frederick, Frederick, MD 21702

Asian soybean rust, caused by the fungal pathogen Phakopsora pachyrhizi, is a potential threat to U.S. soybean production. Asian soybean rust moved from South America and Africa to the United States and was first identified in the United States in 2004. No rust resistance currently exists in commercially available soybean cultivars. Four independent rust resistance genes (Rpp1-Rpp4) have been previously described from noncommercial soybean accessions. The Rpp1 gene confers an immune reaction, in which there are no visible symptoms. In an effort to understand the molecular basis of this specific host resistance, Affymetrix Soybean Genome Arrays were used to identify soybean genes that are expressed in the Rpp1 immune reaction. Soybean plants carrying the Rpp1 gene were sampled at four time points after inoculation with specific isolates of P. pachyrhizi: 6, 12, 24, and 48 h postinoculation. Genes that were induced or suppressed at least 1.5-fold with a P < 0.05 were identified by Blast X similarity searches to proteins in GenBank, and induced/suppressed genes from each time point were compared. Genes encoding heat shock proteins and lipases were differentially expressed at most time points, as were genes with similarity to peroxidases, chitinase, and extensins. In addition, several genes involved in protecting plants from oxidative stress were differentially expressed. This suggests that reactive oxidative species may play a role in the immune reaction. Other biochemical pathways that might be involved in rust resistance will be discussed.

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