Particle gun acceleration appears to be a possible way to transform mycelium cells of obligate plant parasites growing on host surfaces, GUS expression was obtained in E. graminis f.sp. hordei cells after bombardment with the GUS gene under the control of the E. graminis f.sp. hordei beta-tubulin promoter. Three heterologous promoters, one from Aspergillus nidulans and two from Cochliobolus heterostrophus, gave very low or no expression of GUS.