Lux

• 1. Discovery And Identification

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  In 2000, a team at the Plant Gene Expression Center in Berkeley sequenced the LUX gene within Arabidopsis thaliana. This work formed part of the larger Arabidopsis Genome Initiative project. Three years later, researchers from the Salk Institute for Biological Studies used cDNA arrays to identify where this gene expressed itself. By 2005, scientists at Nagoya University and the Scripps Research Institute studied null mutations to prove its necessity. They demonstrated that without LUX, circadian rhythms failed completely in A. thaliana.

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• 2. Molecular Structure And Composition

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  The LUX gene resides on the third chromosome of Arabidopsis thaliana and contains three exons. Upstream lies a promoter with an evening element sequence known as AAAATATCT. This specific DNA pattern appears frequently in genes expressed during the evening hours. The resulting protein spans 323 amino acids and features a Myb-like GARP family domain. This structure allows it to bind directly to DNA sequences for regulation purposes.

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• 3. Circadian Oscillator Mechanism

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  LUX associates with ELF3 and ELF4 proteins to form the Evening Complex during dusk hours. This complex represses transcription of the PRR9 gene which codes for Midday Complex components. PRR9 subsequently suppresses CCA1 and LHY genes that drive morning processes. Light input mechanisms remain unclear despite evidence linking UV-B radiation to induction. The system also represses its own transcription through self-regulation loops within the plant genome.

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• 4. Growth Regulation And Phenotypes

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  Mutants lacking functional LUX fail to repress PIF4 and PIF5 growth factors during nighttime hours. These factors normally inhibit elongation when bound by the Evening Complex. Without repression, early accumulation of PIF4 and PIF5 leads to premature growth. Consequently, these mutants display an elongated hypocotyl phenotype due to excess stem extension at night. Flowering timing shifts as well because PIF4 induces Flowering Locus T expression.

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• 5. Temperature Response Systems

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  High temperatures abolish the association between ELF3 and LUX proteins in experimental settings. Mutants show constitutively high expression of GI, LUX, PRR7, and PRR9 regardless of thermal changes. Normal plants reduce expression of these genes under varying temperature conditions. This suggests LUX detects thermal stress to maintain rhythmic gene output. Temperature may recruit EC components to targeted promoters or disrupt their binding affinity entirely.

• 6. Paralogous Gene Relationships

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  NOX protein forms a complex with ELF3 and ELF4 when LUX is absent from the system. NOX peaks in the late evening and binds DNA sequences similar to those targeted by LUX. Artificial microRNA experiments reveal both proteins are required to recruit the complex to PIF4 and PIF5 promoters. Overexpression of NOX creates long circadian periods while altering CCA1 and TOC1 levels. Null mutations in NOX do not stop rhythms unlike LUX nulls which cause arrhythmia.

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• 7. Evolutionary Orthologs Across Species

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  Pisum sativum contains an ortholog named STERILE NODES that controls photoperiod-sensitive flowering. Lines with this mutation form more vegetative nodes before blooming compared to standard varieties. Hordeum vulgare possesses HvLUX1 identified through the Bowman(eam10) locus mutation. Chlamydomonas reinhardtii features ROC15 and ROC75 as LUX equivalents without known ELF partners. These variants control circadian function but lack full Evening Complex formation outside Arabidopsis thaliana.

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