The gene pyk20 which has been isolated from Arabidopsis thaliana encodes a protein with a glutamine-rich domain in the C-terminal region. The transcription of this gene was shown to be induced in feeding sites of root-parasitic nematodes (Heterodera schachtii), in roots infected by a fungus-like organism (Plasmodiophora brassicae), by plant hormone treatment, and by wounding. In order to identify functional promoter regions seven different 5' and 3' pyk20 promoter (ppyk20) deletion fragments were fused to the uidA gene (gus) and transformed into A. thaliana plants. Histochemical analysis of plants containing the different ppyk20::uidA reporter constructs was performed during plant development in different plant tissues. Comparison of the promoter deletion constructs showed that the region between -277 and -1 bp is necessary to enhance the level of the GUS expression in nematode feeding sites and by plant hormone treatment. The region between -1912 and -278 is essential to provide specificity of GUS expression. Conserved regulatory elements were identified in the ppyk20 by sequence analysis. The activation pattern of ppyk20 makes it well suited to engineer resistance against nematodes and other pathogens.