Abstract
In Arabidopsis thaliana, central circadian clock genes constitute several feedback loops. These interlocking loops generate an ~24-h oscillation that enables plants to anticipate the daily diurnal environment. The identification of additional clock proteins can help dissect the complex nature of the circadian clock. Previously, LIGHT-REGULATED WD1 (LWD1) and LWD2 were identified as two clock proteins regulating circadian period length and photoperiodic flowering. Here, we systematically studied the function of LWD1/2 in the Arabidopsis circadian clock. Analysis of the lwd1 lwd2 double mutant revealed that LWD1/2 plays dual functions in the light input pathway and the regulation of the central oscillator. Promoter:luciferase fusion studies showed that activities of LWD1/2 promoters are rhythmic and depend on functional PSEUDO-RESPONSE REGULATOR9 (PRR9) and PRR7. LWD1/2 is also needed for the expression of PRR9, PRR7, and PRR5. LWD1 is preferentially localized within the nucleus and associates with promoters of PRR9, PRR5, and TOC1 in vivo. Our results support the existence of a positive feedback loop within the Arabidopsis circadian clock. Further mechanistic studies of this positive feedback loop and its regulatory effects on the other clock components will further elucidate the complex nature of the Arabidopsis circadian clock.
Highlights
The circadian clock in many organisms generates an ;24-h oscillation in biochemical, physiological, or behavioral processes to anticipate diurnal changes in the environment (Harmer et al, 2001; Young and Kay, 2001).The circadian system in plants can be separated into three general parts: the input pathway, central oscillator, and output pathway
Our previous study of steady state transcripts of oscillator genes measured by real-time quantitative RT-PCR showed that the lwd1 lwd2 double mutant has a short period phenotype (Wu et al, 2008)
To determine whether LIGHT-REGULATED WD1 (LWD1) and LWD2 regulate the transcriptional activities of oscillator genes, we generated transgenic Arabidopsis harboring promoter:luciferase fusions of central oscillator genes
Summary
The circadian system in plants can be separated into three general parts: the input pathway, central oscillator, and output pathway. The input pathway transmits environmental cues to the central oscillator, which generates a rhythm of the output genes for the control of many physiological progresses, such as photoperiodic flowering. Components functioning in input, central oscillator, or output pathways have been identified (Millar, 2004; Mas, 2005; Gardner et al, 2006; Hotta et al, 2007; Yakir et al, 2007; de Montaigu et al, 2010). PSEUDO-RESPONSE REGULATOR7 (PRR7) and PRR9 function in both the central oscillator and light input
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