SUMMARY Despite considerable technical progress in past years, genetic manipulation of cereals remains a tedious task. Thus, transgenic approaches in monocot species to study plant-microbe interactions are limited to date. Transient gene expression in single epidermal cells mediated by particle bombardment has emerged recently as an attractive alternative for testing the impact of (over-)expressing or silencing single host genes in the context of cereal-powdery mildew interactions. The ease and pace of this assay enables the analysis of candidate genes within a fraction of the time needed to generate stable transgenic lines. Genetically encoded fluorescent sensors expressed in single cells are ideally suited to monitor gene expression, subcellular protein localization and changes of physiological parameters at the single cell level. Likewise, single cell gene expression can be employed to study protein-protein interactions of fluorophore-tagged polypeptides by fluorescence resonance energy transfer or fluorescence (cross) correlation spectroscopy. An integrated approach, combining single cell gene expression technology with modern cell biological tools and single cell sampling via laser capture microdissection, may provide in-depth insights into the molecular events in epidermal host cells in the course of cereal-mildew interactions.