Minisymposium 19: Gene regulation

Abs # 34004: Targets and function of WRKY53 during leaf senescence of Arabidopsis thaliana.

Presenter:	Zentgraf, Ulrike , ulrike.zentgraf@uni-tuebingen.de
Authors	Zentgraf, Ulrike  (A)   Miao, Ying  (A)   Laun, Thomas  (A)
Affiliations:	(A): ZMBP-General Genetics

Arabidopsis WRKY proteins comprise a family of plant specific zinc-finger-type transcription factors involved in the regulation of gene expression during pathogen defense, wounding, trichome development, and senescence. To understand the regulatory role of the senescence related WRKY53 factor, we identified targets of this transcription factor by a pull down assay using genomic DNA and recombinant WRKY53 protein. We isolated a number of candidate target genes including other transcription factors, also of the WRKY family, stress- and defense related genes, and senescence-associated genes (SAGs). The enhanced or reduced expression in the overexpressing and RNAi lines, respectively, strongly confirmed that these candidate genes are correct target genes. WRKY53 protein could bind to these different promoters in vitro and in vivo and it could act either as transcriptional activator or transcriptional repressor depending on the sequences surrounding the W-boxes. Target gene analyses revealed that WRKY53 is also involved in regulation of the catalase genes indicating that WRKY53 either plays a role in oxidative stress response or that the regulation of the hydrogen peroxide level might be involved in leaf senescence. WRKY53 can be induced by H2O2 and can regulate its own expression in a negative feed back loop. Besides WRKY53 itself, one GATA transcription factor and two kinases could by isolated with the yeast one hybrid system interacting with the WRKY53 promoter. MAPKK1 can interact with WRKY53 also on protein level in the yeast two hybrid system and is able to phophorylate WRKY53. The other kinase has a dual function: i) it can bind to WRKY53 promoter and can activate transcription and ii) is not able to phophorylate WRKY53 but can autophosphorylate. Our results suggest that WRKY53 acts in a complex transcription factor signalling network regulating senescence specific gene expression and that hydrogen peroxide might be involved in signal transduction.