CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL Function Synergistically in the Circadian Clock of Arabidopsis

Sheen X Lu,Elaine M Tobin,Stephen M Knowles,Christos Andronis,May S Ong

doi:10.1104/pp.108.133272

Sheen X Lu, Elaine M Tobin + Show 3 more

Open Access

https://doi.org/10.1104/pp.108.133272

Copy DOI

Journal: Plant Physiology	Publication Date: Feb 13, 2009
Citations: 180	License type: CC BY 4.0

Affiliation: University of California, Los Angeles

Abstract

The circadian clock is an endogenous mechanism that coordinates biological processes with daily and seasonal changes in the environment. Heterodimerization of central clock components is an important way of controlling clock function in several different circadian systems. CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) are Myb-related proteins that function in or close to the central oscillator in Arabidopsis (Arabidopsis thaliana). Single mutants of cca1 and lhy have a phenotype of short-period rhythms. cca1 lhy double mutants show an even shorter period phenotype than the cca1 single mutant, suggesting that CCA1 and LHY are only partially functionally redundant. To determine whether CCA1 and LHY act in parallel or synergistically in the circadian clock, we examined their expression in both light-grown and etiolated seedlings. We have shown that LHY and CCA1 bind to the same region of the promoter of a Light-harvesting chlorophyll a/b protein (Lhcb, also known as CAB). CCA1 and LHY can form homodimers, and they also colocalize in the nucleus and heterodimerize in vitro and in vivo. In Arabidopsis, CCA1 and LHY physically interact in a manner independent of photoperiod. Moreover, results from gel filtration chromatography indicate that CCA1 and LHY are present in the same large complex in plants. Taken together, these results imply that CCA1 and LHY function synergistically in regulating circadian rhythms of Arabidopsis.

Highlights

The circadian clock is an endogenous mechanism that coordinates biological processes with daily and seasonal changes in the environment
In Arabidopsis (Arabidopsis thaliana), three genes have been suggested as core components of the central oscillator: CIRCADIAN CLOCK ASSOCIATED1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB EXPRESSION1 (TOC1)
A cca1 lhy Double Mutant Has More Severe Phenotypes Than a cca1 Single Mutant cca1 and lhy single loss-of-function mutants confer short periods (Green and Tobin, 1999; Alabadı et al, 2002; Mizoguchi et al, 2002) and an initial study showed that a cca1 lhy double loss-of-function mutant is unable to maintain rhythms of clockcontrolled RNAs for more than a few cycles under constant light (LL; Alabadı et al, 2002; Mizoguchi et al, 2002)

Summary

Introduction

The circadian clock is an endogenous mechanism that coordinates biological processes with daily and seasonal changes in the environment. CCA1 and LHY bind directly to the promoter of TOC1, CCA1 and LHY are closely related transcription factors that contain a single Myb domain (Wang et al, 1997; Schaffer et al, 1998) They both have circadian rhythms of expression peaking soon after dawn. Cca and lhy single mutants have short-period phenotypes, and overexpression of either gene causes arrhythmicity in expression of clock-regulated genes, leaf movement, and hypocotyl elongation and leads to dramatically reduced levels of endogenous CCA1 and LHY transcripts (Schaffer et al, 1998; Wang and Tobin, 1998; Green and Tobin, 1999; Alabadı et al, 2002; Mizoguchi et al, 2002). These observations suggest that CCA1 and LHY function synergistically in regulating the circadian rhythms of Arabidopsis

Methods

Results

Conclusion