Abstract
Light is an important environmental cue that affects physiology and development of Neurospora crassa. The light-sensing transcription factor (TF) WCC, which consists of the GATA-family TFs WC1 and WC2, is required for light-dependent transcription. SUB1, another GATA-family TF, is not a photoreceptor but has also been implicated in light-inducible gene expression. To assess regulation and organization of the network of light-inducible genes, we analyzed the roles of WCC and SUB1 in light-induced transcription and nucleosome remodeling. We show that SUB1 co-regulates a fraction of light-inducible genes together with the WCC. WCC induces nucleosome eviction at its binding sites. Chromatin remodeling is facilitated by SUB1 but SUB1 cannot activate light-inducible genes in the absence of WCC. We identified FF7, a TF with a putative O-acetyl transferase domain, as an interaction partner of SUB1 and show their cooperation in regulation of a fraction of light-inducible and a much larger number of non light-inducible genes. Our data suggest that WCC acts as a general switch for light-induced chromatin remodeling and gene expression. SUB1 and FF7 synergistically determine the extent of light-induction of target genes in common with WCC but have in addition a role in transcription regulation beyond light-induced gene expression.
Highlights
Organisms synchronize their behavior and physiology with the geophysical day-night cycle by acute signal transduction of rhythmically reoccurring cues and via anticipatory processes controlled by circadian clocks
In this study we have investigated the roles of the Neurospora transcription factors (TFs) White Collar Complex (WCC) and SUB1 in light-activation of transcription
We found that the activity of the main blue-light photoreceptor WCC is essential for the activation of light-inducible genes
Summary
Organisms synchronize their behavior and physiology with the geophysical day-night cycle by acute signal transduction of rhythmically reoccurring cues and via anticipatory processes controlled by circadian clocks. Light-activation of WCC results in dynamic homo-dimerization of WCC protomers, which bind to specific light-responsive DNA elements (LREs) to activate transcription of target genes [15,19,20,21,22]. WCC is the core TF of the circadian clock of Neurospora It supports self-sustained circadian gene expression rhythms in the dark and synchronizes the circadian oscillator with rhythmic exogenous light cues [2,23,24,25,26]. The dark form of WCC supports a low amplitude circadian nucleosome occupancy rhythm at the socalled clock-box in the frq promoter [27,28] while light-activated WCC supports nucleosome remodeling at the light-responsive element (LRE) close to the transcriptional start site [29]. Substantial levels of sub are already expressed in the dark [19,30,31] and SUB1 target genes are still light-inducible to a lower extent in the absence of SUB1 [30] suggesting a more complex regulation of SUB1-dependent light-inducible genes
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