title: The APRR3 component of the clock-associated APRR1/TOC1 quintet is phosphorylated by a novel protein kinase belonging to the WNK family, the gene for which is also transcribed rhythmically in Arabidopsis thaliana.
abstract: 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 h intervals in the order of APRR9-->APRR7-->APRR5-->APRR3-->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 underlying the circadian rhythm in A. 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.
authors.affiliation: Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan.
authors.forename: Masaya
authors.initials: M
authors.lastname: Murakami-Kojima
authors.forename: Norihito
authors.initials: N
authors.lastname: Nakamichi
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yamashino
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002940:Circadian Rhythm / Q000235:genetics; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics*; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D013379:Substrate Specificity; D014157:Transcription Factors; D014158:Transcription, Genetic; D000076204:WNK Lysine-Deficient Protein Kinase 1
chemical_list: C091601:ABI3 protein, Arabidopsis; C448162:APRR3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D010940:Plant Proteins; C411822:TOC1 protein, Arabidopsis; D014157:Transcription Factors; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D000076204:WNK Lysine-Deficient Protein Kinase 1; C465128:WNK1 protein, Arabidopsis