Abstract
Simple SummaryWe observed that both the proximal GATA sequence in light-responsive elements (LREs) of the albino-3 promoter and the Zinc Finger Domain of WC-1 are involved in the dark-related repressive control mechanism of light-regulated genes.Light influences a wide range of physiological processes from prokaryotes to mammals. Neurospora crassa represents an important model system used for studying this signal pathway. At molecular levels, the WHITE COLLAR Complex (WCC), a heterodimer formed by WC-1 (the blue light photo-sensor) and WC-2 (the transcriptional activator), is the critical positive regulator of light-dependent gene expression. GATN (N indicates any other nucleotide) repeats are consensus sequences within the promoters of light-dependent genes recognized by the WCC. The distal GATN is also known as C-box since it is involved in the circadian clock. However, we know very little about the role of the proximal GATN, and the molecular mechanism that controls the transcription of light-induced genes during the dark/light transition it is still unclear. Here we showed a first indication that mutagenesis of the proximal GATA sequence within the target promoter of the albino-3 gene or deletion of the WC-1 zinc finger domain led to a rise in expression of light-dependent genes already in the dark, effectively decoupling light stimuli and transcriptional activation. This is the first observation of cis-/trans-acting repressive machinery, which is not consistent with the light-dependent regulatory mechanism observed in the eukaryotic world so far.
Highlights
Because of the ability to perceive light, organisms can sense the change of time and, anticipate their physiological needs [1,2,3]
Both WHITE COLLAR-1 (WC-1) and WHITE COLLAR-2 (WC-2) contain Pest Arnt Sim (PAS) domains that serve as versatile sensors and interaction modules in signal transduction, and they are necessary for their heterodimerization [18]
WC-1 is Essential for the Proper Assembly of White Collar Complex (WCC) on Light-Regulated Promoters (LRPs)
Summary
Because of the ability to perceive light, organisms can sense the change of time and, anticipate their physiological needs [1,2,3]. Light-induced responses are processes generating hierarchical cascades that involve regulation of gene clusters grouped in two large classes. ELRs show an average peak in mRNA expression at approximately 15 to 30 min after light stimulation Genes regulated in this way are the main circadian clock component frequency (frq), genes involved in carotenoid biosynthesis like albino-1 to albino-3 (al-1–al-3), or photoadaptation genes like vivid (vid) [5,10,11,12,13,14]. Extensive molecular and phenotypical screening led to the identification of only two genes, called wc-1 and wc-2, whose mutations abolished all light responses. WC-1 and WC-2 contain two zinc finger transcription factor plant-like domains [16,17] As transcription factors, both WC-1 and WC-2 bind specific promoter regions called light-responsive elements (LREs). A Neurospora wc-1 strain lacking the zinc finger domain has an impaired circadian rhythm, but it is still capable of gene activation by light [11,30]
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