Minisymposium 27: Growth & Vegetative Development

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Abs # M2703: Regulation of WRKY53 transcription factor in the onset of leaf senescence of Arabidopsis

Presenter:	miao, ying       Contact Presenter
Authors	miao, ying  (A)   laun, thomas  (A)   zentgraf, ulrike  (A)
Affiliations:	(A): ZMBP (center of molecular biology of plants), department of general genetics, university of Tuebingen

The transcription factor WRKY53 plays an important role in the early stage of Arabidopsis senescence but almost nothing is known of how this factor is regulated. Here, we show that the WRKY53 protein exists in an active and inactive form. WRKY53 can interact with a MAP kinase kinase kinase (MEKK1) which contains a NLS and ser/thr protein kinase domain on the protein level and can be phosphorylated in vitro. The DNA binding affinity of WRKY53 is positively influenced by this phosphorylation. In addition, the expression of the WRKY53 gene is activated by MEKK1 binding directly to CA/TNNTG elements of the WRKY53 promoter regulating the switch of leaf age dependent to plant age dependent expression. Microarray data and northern blot results show that MEKK1 has the same expression pattern as WRKY53 during the developmental period of Arabidopsis plants. The inactive WRKY53 protein interacts with UPL, a putative polyubiquitin ligase E3 which consist of a HECT domain, a leucine zipper motif and a C-type lectin motif, and can be polyubiquitinated in vitro. Induction of UPL expression in transgenic plants leads to a decrease of the WRKY53 protein level. In contrast, an UPL knock-out line shows higher WRKY53 protein levels. The results indicate that MEKK1 positively regulates senescence by directly phosphorylating the WRKY53 transcription factor through a shortcut in the MAPK signaling cascade and UPL negatively regulates senescence by targeting WRKY53 for protein degradation.