ZTLs :ZEITLUPE proteins : Photoreceptors at blue wls .Circadian Rythm Oschillator 'entrainer'..
Enhancing / 'augmenting PHY/CRY flowering signals
ZEITLUPE is a circadian photoreceptor stabilized by GIGANTEA in blue light.
Abstract
The circadian clock is essential for coordinating the proper phasing of many important cellular processes. Robust cycling of key clock elements is required to maintain strong circadian oscillations of these clock-controlled outputs. Rhythmic expression of the Arabidopsis thaliana F-box protein ZEITLUPE (ZTL) is necessary to sustain a normal circadian period by controlling the proteasome-dependent degradation of a central clock protein, TIMING OF CAB EXPRESSION 1 (TOC1). ZTL messenger RNA is constitutively expressed, but ZTL protein levels oscillate with a threefold change in amplitude through an unknown mechanism. Here we show that GIGANTEA (GI) is essential to establish and sustain oscillations of ZTL by a direct protein-protein interaction. GI, a large plant-specific protein with a previously undefined molecular role, stabilizes ZTL in vivo. Furthermore, the ZTL-GI interaction is strongly and specifically enhanced by blue light, through the amino-terminal flavin-binding LIGHT, OXYGEN OR VOLTAGE (LOV) domain of ZTL. Mutations within this domain greatly diminish ZTL-GI interactions, leading to strongly reduced ZTL levels. Notably, a C82A mutation in the LOV domain, implicated in the flavin-dependent photochemistry, eliminates blue-light-enhanced binding of GI to ZTL. These data
establish ZTL as a blue-light photoreceptor, which facilitates its own stability through a blue-light-enhanced GI interaction. Because the regulation of GI transcription is clock-controlled, consequent GI protein cycling confers a post-translational rhythm on ZTL protein. This mechanism of establishing and sustaining robust oscillations of ZTL results in the high-amplitude TOC1 rhythms necessary for proper clock function.
https://www.ncbi.nlm.nih.gov/pubmed/17704763
[h=1]GIGANTEA is a nuclear protein involved in phytochrome signaling in
Arabidopsis[/h]
[h=2]Abstract[/h] In a genetic screen of available T-DNA-mutagenized
Arabidopsis populations for loci potentially involved in phytochrome (phy) signaling, we identified a mutant that displayed reduced seedling deetiolation under continuous red light, but little if any change in responsiveness to continuous far-red light. This behavior suggests disruption of phyB, but not phyA signaling. We have cloned the mutant locus by using the T-DNA insertion and found that the disrupted gene is identical to the
recently described GIGANTEA (GI) gene identified as being involved in control of flowering time. The encoded GI polypeptide has no sequence similarity to any known proteins in the database. However, by using β−glucuronidase-GI and green fluorescent protein-GI fusion constructs, we have shown that GI is constitutively targeted to the nucleus in transient transfection assays. Optical sectioning by using the green fluorescent protein-GI fusion protein showed green fluorescence throughout the nucleoplasm. Thus, contrary to previous computer-based predictions that GI would be an integral plasmamembrane-localized polypeptide, the data here indicate that it is a nucleoplasmically localized protein. This result is consistent with the proposed role in phyB signaling, given recent evidence that early phy signaling events are nuclear localized.
http://www.pnas.org/content/97/17/9789.abstract
More about ZTLs (blue light
flowering inhibiting-
to Cannabis - photoreceptors ) :
[h=1]The F-Box Protein ZEITLUPE Confers Dosage-Dependent Control on the Circadian Clock, Photomorphogenesis, and Flowering Time[/h].....the effect of the mutants and overexpressors on period in both light and dark suggests that ZTL
acts as more than a typical photoreceptor. It
may complex with one or more known photoreceptors under some circumstances (e.g., red, blue, or white light) and target one or more proteins for light-dependent degradation......
....
.Presumably for ZTL, under all conditions at least some of the targeted polypeptides are involved in the control of the pace of the oscillator. Hence, unlike the on/off light switch nature of the phytochromes, ZTL may act more like a Y-valve, redirecting the ubiquitinating potential of the participating SCF complex in one direction or another, depending on the light environment.....
http://www.plantcell.org/content/16/3/769.full
More simply ,put ..Blue light affects 'pace' of flowering and maturing time ...
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<=Anthocyanins ...
<= What really happens ,more or less.... 
<RQE per photon wavelength ( nanometers ) 
