Poster: Clocks

Abs # 775: The circadian-associated APRR1/TOC1 quintet of Arabidopsis thaliana, (III):Characterization of APRR3 and its associated novel protein kinase

Presenter:	Murakami, Masaya , masaya-k@mx7.freecom.ne.jp
Authors	Murakami, Masaya  (A)   Mizuno, Takeshi  (A)   Yamashino, Takafumi  (A)
Affiliations:	(A): Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University

In higher plants, clock-controlled circadian rhythms are a longstanding issue in physiology, and a newly emerging paradigm of molecular biology. In the model higher plant Arabidopsis thaliana, several genes have been proposed to encode potential clock-associated components, including a member (APRR1/TOC1) of the pseudo-response regulator family. We previously showed that transcripts of the APRR1/TOC1 family start accumulating after dawn rhythmically and sequentially at approximately 2 hr intervals in the order of APRR9->APRR7->APRR5->APRR1/TOC1. This and other results led us to propose that this APRR1/TOC1 quintet might play coordinate roles in the mechanism underlying circadian rhythms in higher plants. To gain further insight as to such an idea, we here attempt to identify proteins that interact with one of the quintet members, APRR3. The identified component is a novel protein kinase, named WNK1, which is considerably similar to, but clearly distinct from, mitogen-activated protein kinases (MAPKs). It was found that APRR3 is a substrate of this novel protein kinase, the gene for which also shows a rhythmic transcription profile that is well coincident with the APRR3 rhythm. These findings give new insight into the mechanisms underling the circadian rhythm in Arabidopsis thaliana, providing a molecular link between the putative clock component, APRR3, and WNK1, a novel protein kinase that might be implicated as a signal transducer. To further characterize the function of APRR3 with special reference to circadian rhythms, APRR3-overexpressing transgenic lines were established and characterized. These results will be discussed in the context of the APRR1/TOC1 quintet implicated in circadian rhythms in Arabidopsis thaliana.