Poster: Vegetative Development

Abs # 440: Is the WRKY53 transcription factor ofArabidopsis thalianainvolved in regulation of leaf senescence?

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

Senescence is not a chaotic breakdown but an orderly loss of normal cell functions which is under control of the nucleus. As all forms of programmed cell death, it is highly regulated and consumes energy. However, until now, only few data are available concerning the regulating factors of senescence-associated gene expression. The SSH (suppression subtractive hybridization) was performed at a very early time point of leaf senescence when the first reduction of photochemical efficiency can be measured and cab transcripts begin to decline. One of the isolated senescence-associated genes (SAGs) turned out to be a member of the the WRKY superfamily of plant transcription factors. The mRNA level of WRKY53 increased substantially within the rosette leaves of a 6-week-old plant before the expression of SAG12 became detectable, was constant in all leaves of a 7-week-old plant and decreased again in 8-week-old plants. Target gene analyses with recombinant WRKY protein revealed that WRKY53 interacts with the promoter sequences of specific SAGs and of many transcription factors including its own promoter and promoters of other members of the WRKY family. In transient expression assays using Arabidopsis protoplasts it tuned out that WRKY53 can work as either activator or repressor depending on the target gene promoter. This indicates a complex network regulation of transcriptional regulation during leaf senescence. Currently, the expression patterns of different WRKY factors are analyzed in transgenic plants using promoter-GUS constructs. The senescence-specific relevance of WRKY53 is tested by overexpression and RNAi approaches.