Modulation of Circadian Gene Expression and Metabolic Compensation by the RCO-1 Corepressor of Neurospora crassa

Neurospora crassa is a model organism for the study of circadian clocks, molecular machineries that confer approximate to 24-hr rhythms to different processes at the cellular and organismal levels. The FREQUENCY (FRQ) protein is a central component of the Neurospora core clock, a transcription/translation negative feedback loop that controls genome-wide rhythmic gene expression. A genetic screen aimed at determining new components involved in the latter process identified regulation of conidiation 1 (rco-1), the ortholog of the Saccharomyces cerevisiae Tup1 corepressor, as affecting period length. By employing bioluminescent transcriptional and translational fusion reporters, we evaluated frq and FRQ expression levels in the rco-1 mutant background observing that, in contrast to prior reports, frq and FRQ expression are robustly rhythmic in the absence of RCO-1, although both amplitude and period length of the core clock are affected. Moreover, we detected a defect in metabolic compensation, such that high-glucose concentrations in the medium result in a significant decrease in period when RCO-1 is absent. Proteins physically interacting with RCO-1 were identified through co-immunoprecipitation and mass spectrometry; these include several components involved in chromatin remodeling and transcription, some of which, when absent, lead to a slight change in period. In the aggregate, these results indicate a dual role for RCO-1: although it is not essential for core-clock function, it regulates proper period and amplitude of core-clock dynamics and is also required for the rhythmic regulation of several clock-controlled genes.