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Stefanie Traeger, Minou Nowrousian

• Many organisms use circadian clocks to adapt to daily changes in the environment. Major insights into the molecular mechanisms of circadian oscillators have been gained through studies of the model organism \(\textit {Neurospora crassa}\); however, little is known about molecular components of circadian clocks in other fungi. An important part of the \(\textit {N. crassa}\) circadian clock is the \(\textit {frequency (frq)}\) gene, homologs of which can be found in Sordariomycetes, Dothideomycetes, and Leotiomycetes, but not Eurotiomycetes. Recently, we identified a \(\it frq\) homolog in \(\textit {Pyronema confluens}\), a member of the early-diverging Pezizomycete lineage of filamentous ascomycetes. The \(\textit {P. confluens}\) FRQ shares many conserved domains with the \(\textit {N. crassa}\) FRQ. However, there is no known morphological phenotype showing overt circadian rhythmicity in \(\textit {P. confluens}\). To investigate whether a molecular clock is present, we analyzed \(\it frq\) transcription in constant darkness, and found circadian oscillation of \(\it frq\) with a peak in the subjective morning. This rhythm was temperature compensated. To identify additional clock-controlled genes, we performed RNA sequencing of two time points (subjective morning and evening). Circadian expression of two morning-specific genes was verified by reverse transcription quantitative polymerase chain reaction (RT-qPCR) over a full time course, whereas expression of two putative morning-specific and five putative evening-specific genes could not be verified as circadian. \(\it frq\) expression was synchronized, but not entrained by light. In summary, we have found evidence for two of the three main properties of circadian rhythms (free-running rhythm, temperature compensation) in \(\textit {P. confluens,}\) suggesting that a circadian clock with rhythmically expressed \(\it frq\) is present in this basal filamentous ascomycete.