Large-scale gene silencing by RNA interference (RNAi) offers the possibility to address gene function in eukaryotic organisms at a depth unprecedented until recently. Although genome-wide RNAi approaches are being carried out in organisms like Caenorhabditis elegans, Drosophila spp. or human after the corresponding tools had been developed, knock-down of only single or a few genes by RNAi has been reported in plants thus far. Here, we present a method for high-throughput, transient-induced gene silencing (TIGS) by RNAi in barley epidermal cells that is based on biolistic transgene delivery. This method will be useful to address gene function of shoot epidermis resulting in cell-autonomous phenotypes such as resistance or susceptibility to the powdery-mildew fungus Blumeria graminis f. sp. hordei. Gene function in epidermal cell elongation, stomata regulation, or UV resistance might be addressed as well. Libraries of RNAi constructs can be built up by a new, cost-efficient method that combines highly efficient ligation and recombination by the Gateway cloning system. This method allows cloning of any blunt-ended DNA fragment without the need of adaptor sequences. The final RNAi destination vector was found to direct highly efficient RNAi, as reflected by complete knock-down of a cotransformed green fluorescent protein reporter gene as well as by complete phenolcopy of the recessive loss-of-function mlo resistance gene. By using this method, a role of the t-SNARE protein HvSNAP34 in three types of durable, race-nonspecific resistance was observed.