Editing Circadian clock (section)

=== Plant clocks ===
The circadian clock in plants has completely different components to those in the animal, [[fungus]], or bacterial clocks. The plant clock does have a conceptual similarity to the animal clock in that it consists of a series of interlocking transcriptional [[feedback loops]]. The genes involved in the clock show their peak expression at a fixed time of day. The first genes identified in the plant clock were [[TOC1 (gene)|TOC1]], [[CCA1]] and [[LHY]]. The peak expression of the CCA1 and LHY genes occurs at dawn, and the peak expression of the TOC1 gene occurs roughly at dusk. CCA1/LHY and TOC1 proteins repress the expression of each other's genes. The result is that as CCA1/LHY [[protein]] levels start to reduce after dawn, it releases the repression on the TOC1 gene, allowing TOC1 expression and TOC1 protein levels to increase. As TOC1 protein levels increase, it further suppresses the expression of the CCA1 and LHY genes. The opposite of this sequence occurs overnight to re-establish the peak expression of CCA1 and LHY genes at dawn. There is much more complexity built into the clock, with multiple loops involving the PRR genes, the [[ELF4|Evening Complex]] and the light sensitive GIGANTIA and ZEITLUPE proteins.