Maize gene expression during infection with Ustilago maydis strain SG200Dpep1

The basidiomycete Ustilago maydis causes smut disease in maize. Colonization of the host plant is initiated by direct penetration of cuticle and cell wall of maize epidermis cells. The invading hyphae are surrounded by the plant plasma membrane and proliferate within the plant tissue. We identified a novel secreted protein, termed Pep1. Disruption mutants of pep1 are not affected in saprophytic growth and develop normal infection structures. However, Δpep1 mutants fail to penetrate the epidermal cell wall and elicit a strong plant defense response. Using Affymetrix maize arrays we identified about 110 plant genes which are differentially regulated in Δpep1 and wild type infections during the penetration stage. In three independent experiments plants were infected with the strain SG200Dpep1 which is derived from the solopathogenic U. maydis strain SG200. Samples from infected leaves were taken at 24 hours post infection. Samples were treated under the same conditions as described previously.