PRR5 (PSEUDO-RESPONSE REGULATOR 5) plays antagonistic roles to CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1) in Arabidopsis thaliana.

In general, the clock (or oscillator) is central to circadian rhythms in many organisms. In the model higher plant Arabidopsis thaliana, the best candidates for clock components are CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1) and LHY (LATE ELONGATED HYPOCOTYL), which are homologous Myb-related transcription factors. It is also believed that TOC1 (TIMING OF CAB EXPRESSION 1) is another component of the central oscillator.

Molecular dissection of the promoter of the light-induced and circadian-controlled APRR9 gene encoding a clock-associated component of Arabidopsis thaliana.

In the model higher plant Arabidopsis thaliana, a number of circadian clock-associated protein components have recently been identified. Among them, a small family of ARABIDOPSIS PSEUDO-RESPONSE REGULATORS (APRR1/TOC1, APRR3, APRR5, APRR7, and APRR9) is interesting because the most probable clock component TIMING OF CAB EXPRESSION 1 (TOC1) belongs to this family. Several lines of evidence have already been accumulated to support the view that not only APRR1/TOC1 but also other APRR family members are crucial for a better understanding of the molecular link between circadian rhythm and light-signal transduction.

Circadian-controlled basic/helix-loop-helix factor, PIL6, implicated in light-signal transduction in Arabidopsis thaliana.

PHYTOCHROME-INTERACTING FACTOR-LIKE 6 (PIL6) is a member of the large family of basic/helix-loop-helix (bHLH) factors in Arabidopsis thaliana. This circadian-controlled transcription factor was previously suggested to interact with the clock component, TIMING OF CAB EXPRESSION 1 (TOC1). In this study, we isolated a loss-of-function mutant of PIL6, together with a transgenic line aberrantly expressing PIL6 in a manner independent of circadian rhythm.

A Link between circadian-controlled bHLH factors and the APRR1/TOC1 quintet in Arabidopsis thaliana.

APRR1 (ARABIDPSIS PSUEDO-RESPONSE REGULATOR 1) (or TOC1, TIMING OF CAB EXPRESSION 1) is believed to be a crucial component of biological clocks of Arabidopsis thaliana. Nevertheless, its molecular function remains to be fully elucidated. Based on the results of yeast two-hybrid and in vitro binding assays, we previously showed that APRR1/TOC1 interacts with certain bHLH factors (i.