A Circadian Clock-Regulated Toggle Switch Explains AtGRP7 and AtGRP8 Oscillations in Arabidopsis thaliana
Figure 1
Proposed network structure and mechanism of AtGRP7 and AtGRP8 auto-regulation and cross-regulation.
A) The circadian core oscillator is synchronized to the rhythm of a given external zeitgeber signal. It drives the slave oscillator composed of AtGRP7 and AtGRP8 (since the core oscillator genes LHY/CCA1 are assumed to inhibit the transcription of AtGRP7 and AtGRP8). AtGRP7 and AtGRP8 negatively auto-regulate and cross-regulate each other. B) The negative auto-regulation and cross-regulation involves an alternative splicing mechanism coupled to NMD [73]: The AtGRP7 pre-mRNA consists of two exons (green), separated by an intron (yellow) and bounded by the and
untranslated region (UTR) (gray). Its mature mRNA, with the intron completely spliced out, can produce functional protein (red). Both AtGRP7 as well as AtGRP8 protein can bind the AtGRP7 pre-mRNA and induce the production of an alternatively spliced mRNA variant, retaining the first half of the intron. This alternatively spliced mRNA cannot produce functional protein due to a premature termination codon and is degraded via NMD.