Arabidopsis MEKK1 can take a short cut: it can directly interact with senescence-related WRKY53 transcription factor on the protein level and can bind to its promoter.
Despite the importance of the senescence processes in plants, our knowledge on regulatory mechanisms of senescence is still poor. WRKY transcription factors have been shown to be involved in the regulation of leaf senescence. However, almost nothing is known about the upstream regulation of the senescence specific expression of WRKY factors. Therefore, we characterized proteins that bind and activate the promoter of WRKY53, which participates in leaf senescence in Arabidopsis thaliana. Surprisingly, a mitogen activated protein kinase kinase kinase (MEKK1) was identified as a DNA-binding protein. The binding motif for MEKK1 in the WRKY53 promoter could be characterized and promoter:GUS analyses revealed that this region is important for the switch of WRKY53 expression from a leaf age dependent to a systemic plant age dependent expression during bolting time. In addition to its promotor-binding activity, MEKK1 was also able to interact with the WRKY53 protein. Using bimolecular fluorescence complementation assays the complex formation of MEKK1 and WRKY53 could be localized predominately in the nucleus of Arabidopsis cells. MEKK1 could also phosphorylate WRKY53 in vitro and phosphorylation could increase DNA-binding activity of WRKY53 in vitro and transcription of a WRKY53 promoter driven reporter gene in vivo. These results suggest that MEKK1 is a bifunctional protein: it binds to the promoter of the WRKY53 gene regulating the switch from a leaf age dependent to a plant age dependent expression and it can phosopharylate WRKY53 in vitro increasing its DNA binding activity. Thus, MEKK1 might be able to take a very direct short cut in mitogen-activated protein kinase (MAPK) signalling by directly phosphorylating a transcription factor.
Miao
Ying
Y
Department of General Genetics, ZMBP (Centre of Molecular Biology of Plants), University of Tuebingen, Auf der Morgenstelle 28, Tuebingen, Germany.
Laun
Thomas M
TM
Smykowski
Anja
A
Zentgraf
Ulrike
U
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006861:Hydrogen Peroxide / Q000494:pharmacology; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000235:genetics; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C496136:WRKY53 protein, Arabidopsis; D006861:Hydrogen Peroxide; D048728:MAP Kinase Kinase Kinase 1