Root exudate impact on gene expression of Sporisorium reilianum.

Sporisorium reilianum f.sp zeae, a basidiomycetous fungus belonging to Ustilaginaceae, is the causal agent of the maize head smut disease. This soilborne pathogen infects the host plant at the seedling stage by penetrating roots. The infection is systemic, and disease symptoms become apparent only after the onset of flower development when the fungal sori replace male or female inflorescences. In order to investigate the mechanism of infection, we analysed the transcriptome of the fungus in response to root exudates during the previous phase of infection. A suppression subtractive hybridization (SSH) was used to generate cDNA libraries representing genes differentially expressed in haploid cell forms of the fungus exposed to root exudates Leading to 960 ESTs. By using cDNA macroarray hybridization, we identified 36 ESTs which were differentially expressed in response to exudates application. In this first transcriptomic analysis realized on S. reilianum, we show that maize root exudates may affect gene expression of the fungus involved in cell respiration, cell wall development, metabolism and hypothetical proteins during the previous step of infection and could play an important role in fungi growth promotion and plant pathogenesis.