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7

Molecular characterization of the Asian soybean rust disease in resistant and susceptible soybean lines

Presenter: M. Van de Mortel

All authors and affiliations: M. VAN DE MORTEL (1), J. C. Recknor (2), D. S. Nettleton (2), C. V. Godoy (3), R. V. Abdelnoor (3), . M. R. Almeida (3), T. J. Baum (1), and S. A. Whitham (1). (1) Department of Plant Pathology and (2) Department of Statistics, Iowa State University, Ames, IA 50011; and (3) Embrapa Soybean, Cx P 231, Londrina, 86001-970, PR, Brazil

Our goal is to acquire critical molecular data on the Asian soybean rust (ASR) infection process in susceptible and resistant soybean cultivars. To define specific molecular events in the soybean plant that are associated with ASR resistance and susceptibility, we detected gene expression over a 7-day time course in both ASR- and mock-infected leaves from susceptible and resistant (Rpp2) cultivars by using Affymetrix Soybean GeneChip microarrays. Statistical analysis showed that 1,516 and 894 genes in the susceptible and resistant cultivars, respectively, significantly changed expression. Most genes were differentially expressed within the first 3 days after infection (dai), followed by a 2-day time period in which very few genes were differentially expressed. After 4 dai, host gene expression diverged again between mock- and ASR-infected leaves. Arabidopsis homologs were identified for 1,302 and 773 differentially regulated genes in the susceptible and resistant cultivars, respectively, which allowed us to perform functional classification. These analyses revealed that genes with functions in metabolism and disease/defense were statistically overrepresented in both the susceptible and resistant cultivars gene lists. ASR-regulated genes involved in signal transduction and energy generation were overrepresented in the susceptible cultivar, while genes with functions in transport and transcription were overrepresented in the resistant cultivar. ASR-regulated genes involved in post-transcriptional regulation or with no known function were underrepresented in both cultivars, and genes involved in cell structure, growth and development, and protein synthesis appeared to be underrepresented in the resistant cultivar.

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