Abstract
band
, an allele enabling clear visualization of circadianly regulated spore formation (conidial banding), has remained an integral tool in the study of circadian rhythms for 40 years.
bd
was mapped using single-nucleotide polymorphisms (SNPs), cloned, and determined to be a T79I point mutation in
ras-1
. Alterations in light-regulated gene expression in the
ras-1
bd
mutant suggests that the
Neurospora
photoreceptor WHITE COLLAR-1 is a target of RAS signaling, and increases in transcription of both
wc-1
and
fluffy
show that regulators of conidiation are elevated in
ras-1
bd
. Comparison of
ras-1
bd
with dominant active and dominant-negative
ras-1
mutants and biochemical assays of RAS function indicate that RAS-1
bd
displays a modest enhancement of GDP/GTP exchange and no change in GTPase activity. Because the circadian clock in
ras-1
bd
appears to be normal,
ras-1
bd
apparently acts to amplify a subtle endogenous clock output signal under standard assay conditions. Reactive oxygen species (ROS), which can affect and be affected by RAS signaling, increase conidiation, suggesting a link between generation of ROS and RAS-1 signaling; surprisingly, however, ROS levels are not elevated in
ras-1
bd
. The data suggest that interconnected RAS- and ROS-responsive signaling pathways regulate the amplitude of circadian- and light-regulated gene expression in
Neurospora
.