Conidiation rhythm and light entrainment in superoxide dismutase mutant in Neurospora crassa.

Conidial formation in the filamentous fungus Neurospora crassa is regulated by nutritional conditions, light, and the circadian clock. We found that a sod-1 mutant, with a defective superoxide dismutase catalyzing the conversion of superoxide to hydrogen peroxide, had a slightly shorter period length than the wild type and clear conidial banding similar to a mutant of band (bd). However, unlike the bd mutant, the sod-1 mutant could sustain conidial banding with light pulses on a nutrient-rich medium, which involved an enhancement of the light-induced transcription of frequency (frq). sod-1 was hypersensitive to entrainment of the conidiation rhythm by light in race tubes. Furthermore, a frq(10); sod-1 double mutant showed conidiation rhythm in darkness and could be synchronized to light/dark cycles by the masking effect of light. These genetic analyses suggested that intracellular reactive oxygen species (ROS) act on circadian conidiation via multiple circadian clocks and output pathways.