Early nuclear events in plant defence signalling: rapid gene activation byWRKY transcription factors

Parsley WRKY proteins comprise a family of plant-specific zinc-finger-type factors implicated in the regulation of genes associated with pathogen defe nce. In vitro, these proteins bind specifically to functionally defined TGA C-containing Mi box promoter elements within the Pathogenesis-Related Class 10 (PR-10) genes. Here we present in vivo data demonstrating that WRKY1 is a transcriptional activator mediating fungal elicitor-induced gene express ion by binding to W box elements. In situ RNA hybridization revealed that t he WRKY1 gene is rapidly and locally activated in parsley leaf tissue aroun d fungal infection sites. Transient expression studies in parsley protoplas ts shelved that a specific arrangement of W box elements in the WRKY1 promo ter itself is necessary and sufficient for early activation and that WRKY1 binds to such elements. Our results demonstrate that WRKY transcription fac tors play an important role in the regulation of early defence-response gen es including regulation of WRKY1.