High impact information on CCA1

• Furthermore, the expression of both endogenous CCA1 and the related LHY gene was suppressed [1].
• Constitutive expression of CCA1 protein in transgenic plants abolished the circadian rhythm of several genes with dramatically different phases [1].
• The MYB transcription factors LHY and CCA1 negatively regulate TOC1 expression [2].
• Numerical simulations using the interlocking-loop model show that balancing LHY/CCA1 function against GI and other evening-expressed genes can largely account for temperature compensation in wild-type plants and the temperature-specific phenotypes of gi mutants [3].
• In wild-type Arabidopsis plants grown in continuous light, the EPR1 transcript exhibits circadian rhythmicity similar to that of CCA1 and LHY [4].

Biological context of CCA1

• We show that prr9 and prr5 null mutants have reciprocal period defects for multiple circadian rhythms, consistent with subtly altered expression patterns of CCA1 and TOC1 [5].
• We conclude that the CCA1 protein is a key element in the functioning of the phytochrome signal transduction pathway leading to increased transcription of this Lhcb gene in Arabidopsis [6].
• The circadian clock-associated 1 (CCA1) gene encodes a Myb-related transcription factor that has been shown to be involved in the phytochrome regulation of Lhcb1*3 gene expression and in the function of the circadian oscillator in Arabidopsis thaliana [7].
• CK2 beta-subunits stimulate binding of CCA1 to the CCA1 binding site on the Lhcb1*3 gene promoter, and recombinant CK2 is able to phosphorylate CCA1 in vitro [7].
• CCA1 phosphorylation by CK2 is necessary for its ability to form an homodimer [8].
• Our results indicate that CCA1 is an important clock-associated protein involved in circadian regulation of gene expression [9].
• LHY/CCA1-like genes are typified by the presence of nine highly conserved domains (C1-C9) in higher plants [10].

Associations of CCA1 with chemical compounds

• Lines of transgenic Arabidopsis plants expressing antisense RNA for CCA1 showed reduced phytochrome induction of the endogenous Lhcb1*3 gene, whereas expression of another phytochrome-regulated gene, rbcS-1A, which encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was not affected [6].
• Maintenance of the CCA1/LHY-TOC1 molecular oscillator at these temperatures in oil palm allows for the possibility that this system is involved in the control of isoprene emission rhythms [11].
• In addition, ethylene production is controlled by the TIMING OF CAB EXPRESSION 1 and CIRCADIAN CLOCK ASSOCIATED 1 genes, which are critical for all circadian rhythms yet tested in Arabidopsis [12].

Physical interactions of CCA1

• CKB3 interacts specifically with CCA1 both in a yeast two-hybrid system and in an in vitro interaction assay [7].
• A yeast two-hybrid (Y2H) assay revealed that only the Ser-484 site, not the other five Ser sites was critical for CCA1 homodimer formation [10].

Regulatory relationships of CCA1

• ELF3 is also necessary for light-induced CCA1/LHY expression, but it is neither light-induced nor clock-regulated during de-etiolation [13].
• ELF4 is a phytochrome-regulated component of a negative-feedback loop involving the central oscillator components CCA1 and LHY [13].
• However, GBSSI activity shows a clear oscillation with a period of 24 h that is altered in transgenic plants over-expressing CCA1 [14].

Other interactions of CCA1

• Reciprocal regulation between TOC1 and LHY/CCA1 within the Arabidopsis circadian clock [2].
• Evidence will be provided that PRR5 plays an antagonistic role(s) to the putative CCA1 clock component [15].
• The data are also consistent with LUX being necessary for activation of CCA1 and LHY expression [16].
• Genetic analysis suggests that SRR1 works both in the phyB pathway but also independently of phyB. srr1 mutants are affected in multiple outputs of the circadian clock in continuous light conditions, including leaf movement and expression of the clock components, CCA1 and TOC1 [17].
• Recently, this locus was identified as EARLY FLOWERING 4, a gene implicated in floral induction and regulating the expression of the gene CIRCADIAN CLOCK-ASSOCIATED 1 [18].

References