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

Consuelo Olivares-Yañez, Jillian Emerson, Arminja Kettenbach, Jennifer J Loros, Jay C Dunlap, Luis F Larrondo

Neurospora crassa is a model organism for the study of circadian clocks, molecular machineries that confer circa 24 h rhythms to different processes at the cellular and organismal level. 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 rco-1 (regulation of conidiation-1), the ortholog of the Saccharomyces cerevisiae Tup1 co-repressor, 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.