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Abstract
Ustilago maydis (U. maydis) is the causal agent of corn smut and is responsible for significant yield losses of approximately $1.24 billion annually in the United States. The infected plants show gall formation on all the aerial parts of the plant. Significant economic loss occurs due to infected kernels that cannot be used for food or fuel production. Several methods are utilized to control corn smut disease however; host resistance is the only practical method for managing common smut. Currently, there are no known maize lines that are resistant to U. maydis. It is therefore necessary to identify new sources of resistance to U. maydis. We have identified maize, teosinte and maize-teosinte introgression lines (NILs) with a high level of resistance to U. maydis. This is the first report of the identification of new sources of resistance to U. maydis from teosinte and maize-teosinte NILs. The teosinte introgressed region present in the resistant NIL is 3.6Mbp in size and carries 7 genes that may be contributing to the resistant phenotype. To identify genes expressed in response and U. maydis infection in an incompatible reaction, transcriptome profiling was conducted on maize genotypes demonstrating resistance and susceptibility to U. maydis. Among the 17,555 genes monitored using Affymetrix GeneChip maize genome array, 5,639 genes showed significant differential expression between the control and U. maydis inoculated maize lines at 24 hours post inoculation (hpi). The up-regulated genes (1.5 fold change) were grouped into 7 categories, and were classified as genes coding for proteins associated with defense related genes, enzyme families, receptor like kinases, photosynthesis, regulation overview and transcription. The down regulated genes ( 1.5 fold change) were grouped into 10 categories representing genes involved in enzyme families, hormones, plant glycolysis, photosynthesis, metabolism, cell function, transcription, defense related genes, receptor like kinases and regulation overview. These findings provide insight into the complexity of biotrophic interactions in an incompatible interaction and indicate that the activation of plant defenses in response to U. maydis infection is similar to other biotrophic interactions.