Overexpression of White Collar-1 (WC-1) activates circadian clock-associated genes, but is not sufficient to induce most light-regulated gene expression in Neurospora crassa.
Many processes in fungi are regulated by light, but the molecular mechanisms are not well understood. The White Collar-1 (WC-1) protein is required for all known blue-light responses in Neurospora crassa. In response to light, WC-1 levels increase, and the protein is transiently phosphorylated. To test the hypothesis that the increase in WC-1 levels after light treatment is sufficient to activate light-regulated gene expression, we used microarrays to identify genes that respond to light treatment. We then overexpressed WC-1 in dark-grown tissue and used the microarrays to identify genes regulated by an increase in WC-1 levels. We found that 3% of the genes were responsive to light, whereas 7% of the genes were responsive to WC-1 overexpression in the dark. However, only four out of 22 light-induced genes were also induced by WC-1 overexpression, demonstrating that changes in the levels of WC-1 are not sufficient to activate all light-responsive genes. The WC proteins are also required for circadian rhythms in dark-grown cultures and for light entrainment of the circadian clock, and WC-1 protein levels show a circadian rhythm in the dark. We found that representative samples of the mRNAs induced by over-expression of WC-1 show circadian fluctuations in their levels. These data suggest that WC-1 can mediate both light and circadian responses, with an increase in WC-1 levels affecting circadian clock-responsive gene regulation and other features of WC-1, possibly its phosphorylation, affecting light-responsive gene regulation.
Program in Biological Clocks, Department of Biology, Texas A & M University, College Station, TX 77843, USA.
Z A
ZA
Lewis
A
A
Correa
C
C
Schwerdtfeger
K L
KL
Link
X
X
Xie
R H
RH
Gomer
T
T
Thomas
D J
DJ
Ebbole
D
D
Bell-Pedersen
D002940:Circadian Rhythm / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D005656:Fungal Proteins; D015966:Gene Expression Regulation, Fungal / Q000528:radiation effects*; D005800:Genes, Fungal; D008027:Light; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000235:genetics*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics*
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D014157:Transcription Factors; C105589:wc-1 protein, Neurospora crassa