Arabidopsis thaliana circadian clock is regulated by the small GTPase LIP1.
BACKGROUND
At the core of the eukaryotic circadian network, clock genes/proteins form multiple transcriptional/translational negative-feedback loops and generate a basic approximately 24 hr oscillation, which provides daily regulation for a wide range of processes. This temporal organization enhances the fitness of the organism only if it corresponds to the natural day/night cycles. Light is the most effective signal in synchronizing the oscillator to environmental cycles.


RESULTS
The lip1-1 (light insensitive period 1) mutant isolated from the model plant Arabidopsis thaliana displays novel circadian phenotypes arising from specific defects in the light input pathway to the oscillator. In wild-type plants, period length shortens with increasing light fluence rates and the phase of rhythms can be shifted by light pulses administered to dark-adapted plants. In contrast, in lip1-1, period length is nearly insensitive to light intensity and significantly larger phase shifts (delays) can be induced during the subjective night. The mutant also displays elevated photomorphogenic responses to red and blue light, which cannot be explained by the circadian defect, suggesting distinct functions for LIP1 in the circadian light input and photomorphogenesis. The LIP1 gene encodes a functional, plant-specific atypical small GTPase, and therefore we postulate that it acts similarly to ZEITLUPE at postranscriptional level.


CONCLUSIONS
LIP1 represents the first small GTPase implicated in the circadian system of plants. LIP1 plays a unique negative role in controlling circadian light input and is required for precise entrainment of the plant clock.
Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, Hungary.
Eva
E
Kevei
Péter
P
Gyula
Balázs
B
Fehér
Réka
R
Tóth
András
A
Viczián
Stefan
S
Kircher
Dean
D
Rea
Dulguun
D
Dorjgotov
Eberhard
E
Schäfer
Andrew J
AJ
Millar
László
L
Kozma-Bognár
Ferenc
F
Nagy
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D008027:Light; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism
D029681:Arabidopsis Proteins; D012333:RNA, Messenger; C525435:LIP1 small GTPase, Arabidopsis; D020559:Monomeric GTP-Binding Proteins