The synchronization and adaptation of Neurospora crassa circadian and conidiation rhythms to short light-dark cycles

Abstract

Circadian clocks control the physiological and behavioral daily rhythms to adapt to the changing environment with a period of ~24 h. However, the influence and mechanism of extreme light-dark cycles on the circadian clock remain unclear. We show that, in the fungus Neurospora crassa under short LD cycles, both the growth rate and the ratio of microconidia production contributes to adaptation in LD12:12 (light for 12 h and dark for 12 h, periodically). Mathematical modeling and experiments demonstrate that in short LD cycles, the expression of the core clock protein FREQUENCY is entrained to the LD cycles when LD>3:3 while it free runs when T[≤] LD3:3. We investigated the changes in circadian/diurnal rhythms under a series of different LD conditions, and the results showed that conidial rhythmicity can be adapted to the short LD cycles. We further demonstrate that the existence of unknown blue light photoreceptor(s) and the circadian clock might promote the conidiation rhythms that resonate with the environment. A high-intensity light induced the expression of a set of downstream genes involved in various metabolic pathways. The ubiquitin E3 ligase FWD-1 and the previously described CRY-dependent oscillator system were implicated in regulating conidiation under short LD conditions.