LUX

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LUX ARRHYTHMO (LUX) is a gene in Arabidopsis thaliana that codes for the LUX ARRHYTHMO protein, a transcription factor needed for the plant’s circadian clock. LUX teams up with ELF3 and ELF4 to form the Evening Complex (EC), a key part of the plant’s clockwork that is active in the evening and helps repress the gene PRR9, which is part of the Midday Complex.

As part of the EC, LUX helps turn down the activity of several growth-related and clock genes. It represses PIF4 and PIF5, which are important for growth and flowering signals. By keeping these genes in check in the evening, the EC slows growth at night. LUX also keeps its own transcription in check as part of the clock’s feedback loops.

The LUX gene has an “evening element” (EE) in its promoter with the sequence AAAATATCT. This element helps regulate LUX expression, likely through binding by other clock proteins such as CCA1 and LHY. The LUX protein itself is 323 amino acids long and has a DNA-binding domain similar to other Myb-like transcription factors.

Mutations that remove LUX disrupt the clock, making plants arrhythmic and often causing longer hypocotyls due to excess night-time growth. Temperature can affect clock components, and LUX mutants show unusual, constitutively high expression of several clock and growth genes regardless of temperature changes. The EC’s ability to respond to temperature may depend on how LUX interacts with ELF3 and ELF4.

LUX has a paralog called NOX (BOA), which can partner with ELF3 and ELF4 when LUX is absent. NOX also binds similar DNA sequences and influences the clock, but knocking down NOX does not completely stop circadian rhythms, indicating LUX and NOX have distinct roles.

Similar genes exist in other species. For example, Pisum sativum has STERILE NODES (SN), a functional relative of LUX, and barley has HvLUX1. Other plants have related clock genes, but it is not always clear whether they form the same Evening Complex outside Arabidopsis.

LUX was first sequenced in 2000, and its expression in Arabidopsis was shown in 2003. In 2005, researchers demonstrated that LUX and the Evening Complex are necessary for proper circadian rhythms in Arabidopsis thaliana.