Early nuclear events in plant defence signalling: rapid gene activation by WRKY transcription factors.

Parsley WRKY proteins comprise a family of plant-specific zinc-finger-type factors implicated in the regulation of genes associated with pathogen defence. In vitro, these proteins bind specifically to functionally defined TGAC-containing W box promoter elements within the Pathogenesis-Related Class10 (PR-10) genes. Here we present in vivo data demonstrating that WRKY1 is a transcriptional activator mediating fungal elicitor-induced gene expression by binding to W box elements. In situ RNA hybridization revealed that the WRKY1 gene is rapidly and locally activated in parsley leaf tissue around fungal infection sites. Transient expression studies in parsley protoplasts showed that a specific arrangement of W box elements in the WRKY1 promoter itself is necessary and sufficient for early activation and that WRKY1 binds to such elements. Our results demonstrate that WRKY transcription factors play an important role in the regulation of early defence-response genes including regulation of WRKY1.