RNA-binding proteins and circadian rhythms in
Arabidopsis thaliana
An Arabidopsis transcript preferentially expressed at the end of the daily light period codes for the RNA–binding protein At GRP7. A reverse genetic approach in Arabidopsis thaliana has revealed its role in the generation of circadian rhythmicity: At GRP7 is part of a negative feedback loop through which it influences the oscillations of its own transcript. Biochemical and genetic experiments indicate a mechanism for this autoregulatory circuit: At grp7 gene transcription is rhythmically activated by the circadian clock during the day. The At GPR7 protein accumulates with a certain delay and represses further accumulation of its transcript, presumably at the post–transcriptional level. In this respect, the At GRP7 feedback loop differs from known circadian oscillators in the fruitfly Drosophila and mammals based on oscillating clock proteins that repress transcription of their own genes with a 24 h rhythm. It is proposed that the At GRP7 feedback loop may act within an output pathway from the Arabidopsis clock.