Project description:Infection-related development of phytopathogenic fungi is initiated by sensing and responding to plant surface cues. This response results in the formation of specialized infection structures, so-called appressoria. To unravel the program inducing appressoria in the biotrophic smut fungus Ustilago maydis, we exposed cells to a hydrophobic surface and the cutin monomer 16-hydroxy hexadecanoic acid. Genome-wide transcriptional profiling under these appressorium-inducing in vitro conditions revealed dramatic transcriptional changes in almost 20% of the genes. Comparisons with the U. maydis sho1 msb2 double mutant, lacking two putative sensors for plant surface cues, revealed that these plasma membrane receptors regulate a small subset of the surface cue-induced genes. These genes comprised mainly secreted proteins including plant cell wall degrading enzymes that facilitate plant penetration and secreted effectors that are essential virulence factors, with functions after penetration. Our data also demonstrate specific effects on two transcription factors that redirect the transcriptional regulatory network towards appressorium formation and plant penetration. Thus, plant surface cues prime U. maydis for biotrophic development. Solopathogenic Ustilago maydis strain AM1 and its derivate AM1Δsho1Δmsb2 were grown to mid-log phase in YEPSL medium and resuspended in 2% YEPSL plus/minus 16-hydroxy hexadecanoic acid (HDA). The cell suspensions were sprayed on hydrophobic surface (Parafilm) and incubated for 12 h. As control, cells were sprayed on hydrophilic glass surface and incubated for 2 h. After RNA extraction Affymetrix microarrays were performed.
