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

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.

MYB transcription factor genes as regulators for plant responses: an overview

“…The R3-type, TRIPTYCHON (TRY), CAPRICE (CPC) and MYBL2, are likely to have evolved from R2R3-MYB genes and involved in the control of cellular morphogenesis (Pesch and Hulskamp 2009) and in secondary metabolism control (Dubos et al 2008). Those MYB-related genes of the evolutionarily older R1/R2-type, including CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), encode core components of the central circadian oscillator (Lu et al 2009 The various functions of MYB are enlisted in Table 1 and discussed below-…”

Deregulated Copper Transport Affects Arabidopsis Development Especially in the Absence of Environmental Cycles

“…Among the main central clock components in Arabidopsis are the single Myb domain transcription factors CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY; for review, see McClung, 2006;Harmer, 2009;Mas and Yanovsky, 2009). The LHY and CCA1 proteins bind to the same region of their target promoters, form homodimers or heterodimers, and colocalize within the nucleus, where they function synergistically (Lu et al, 2009). The loss-of-function double mutants lhy cca1 show short periods of free-running circadian rhythms, affected photoperiodic control of flowering time, modified hypocotyl length, and reduced plant height (Mizoguchi et al, 2002(Mizoguchi et al, , 2005Ito et al, 2007;Niwa et al, 2007;Lu et al, 2009).…”

Physiological and Genetic Bases of the Circadian Clock in Plants and Their Relationship with Herbicides Efficacy

“…At 12 p.m., the amounts of H 2 O 2 and catalases were higher in comparison to the evaluations conducted at 12 a.m. Since the transcription of the CCA1 gene reduces as the nighttime approaches (Lu et al, 2009), the activity of catalase enzymes also decreases, making plants more sensitive to the oxidative stress caused by the application of the paraquat herbicide during the evening.…”

“…The amounts of transcripts and proteins are highly abundant during the morning (Lu et al, 2009). These proteins act to inhibit the expression of the TOC1 (TIMING OF CAB EXPRESSION) gene, the main component of the evening phase of the circadian clock, also known as PRR1 (PSEUDO-RESPONSE REGULATOR 1).…”