Transcription factor CBF-1 is critical for circadian gene expression by modulating WHITE COLLAR complex recruitment to the frq locus.

Xuemei Cao,Yumeng Fan,Jiabin Duan,Yi Liu,Qun He,Hongda Li,Xiao Liu,Gregory P. Copenhaver

doi:10.1371/journal.pgen.1007570

Xuemei Cao, Yumeng Fan + Show 6 more

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https://doi.org/10.1371/journal.pgen.1007570

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Abstract

Transcription of the Neurospora crassa circadian clock gene frequency (frq) is an essential process in the negative feedback loop that controls circadian rhythms. WHITE COLLAR 1 (WC-1) and WHITE COLLAR 2 (WC-2) forms the WC complex (WCC) that is the main activator of frq transcription by binding to its promoter. Here, we show that Centromere Binding Factor 1 (CBF-1) is a critical component of the N. crassa circadian clock by regulating frq transcription. Deletion of cbf-1 resulted in long period and low amplitude rhythms, whereas overexpression of CBF-1 abolished the circadian rhythms. Loss of CBF-1 resulted in WC-independent FRQ expression and suppression of WCC activity. As WCC, CBF-1 also binds to the C-box at the frq promoter. Overexpression of CBF-1 impaired WCC binding to the C-box to suppress frq transcription. Together, our results suggest that the proper level of CBF-1 is critical for circadian clock function by suppressing WC-independent FRQ expression and by regulating WCC binding to the frq promoter.

Highlights

Circadian rhythms exist in almost all kingdoms of life [1,2,3]
We showed that the transcription factor Centromere Binding Factor 1 (CBF-1) functions as a repressor to modulate WC complex (WCC) recruitment to the C-box of frq promoter
Our data showed that deletion or overexpression of CBF-1 dampened circadian rhythm due to impaired WCC binding at the frq promoter

Summary

Introduction

The circadian clock is a highly conserved timekeeping system that allows organisms to anticipate and adjust to daily environmental changes [4]. These rhythms are generated by self-sustained molecular oscillators, based on transcription-translation negative feedback loops in eukaryotic model organisms [1]. In the N. crassa circadian system, WC-1 and WC-2, two PER-ARNT-SIM (PAS) domaincontaining transcription factors, form a heterodimeric complex (WCC) that initiates transcription of the clock gene frq through binding to PLRE and C-box regulatory sequences [9, 10]. FRQ protein dimerizes and forms a complex with FRH, functioning as the negative element in the circadian negative-feedback loop [11]. When FRQ protein becomes extensively phosphorylated, it is ubiquitinated by an E3 ligase complex and degraded through the proteasome, allowing the cycle to restart [19,20,21,22]

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