Using a promoter tagging approach, a gene upregulated in nematode feeding structures (NFS) of Heterodera schachtii was identified in Arabidopsis thaliana plants. Sequence analysis of the transgenic line bearing gus reporter gene and the wild-type plant revealed that the T-DNA had been inserted into the promoter of the gene, however, with transcription start points at different sites for the gus reporter gene and for the endogenous gene. This tagged gene, designated pyk20, encodes a transcript of 2.6 kb. Southern blot analysis revealed a single gene copy for pyk20 in the Arabidopsis C-24 genome. Other cruciferous plants were shown to possess pyk20 or homologous genes. The predicted amino acid sequence of the PYK20 protein contains 695 residues with a molecular mass of 78 kDa and includes a glutamine-rich domain in the C-terminal region. IAA and kinetin treatment increased the level of the pyk20 transcript in the plant, whereas ABA treatment and temperature stress reduced the pyk20 transcript level. In-situ hybridisation and Northern blot analysis revealed that the gene is expressed in NFS. Based on homologies of the glutamine-rich domain, the biological role of the pyk20 gene product as a transcription factor is assumed.