White collar-1, a DNA binding transcription factor and a light sensor

Area of Science:

• Mycology
• Molecular Biology
• Chronobiology

Background:

• Blue light influences numerous fungal physiological processes.
• The specific photoreceptors responsible for these light responses in fungi remain largely unidentified.
• In Neurospora crassa, the Per-Arnt-Sim (PAS) domain transcription factor white collar-1 (WC-1) is known to mediate all light responses.

Purpose of the Study:

• To investigate the role of the WC-1 protein in blue-light perception and circadian clock regulation in Neurospora crassa.
• To determine if WC-1 functions as the blue-light photoreceptor in this fungal species.

Main Methods:

• Genetic manipulation of the WC-1 protein, specifically removing its light, oxygen, or voltage (LOV) domain.
• Assessing light-dependent physiological responses, including circadian clock entrainment.
• Investigating temperature entrainment of the circadian clock in mutant strains.
• Biochemical analysis of the WC-1-WC-2 protein complex to identify associated chromophores.

Main Results:

• Deletion of the WC-1 LOV domain abolished all light responses, including circadian clock entrainment by light.
• WC-1-mediated dark activation of the frq gene remained unaffected in the mutant.
• The circadian clock in the mutant strain could still be entrained by temperature.
• Purified WC-1-WC-2 protein complexes were found to contain flavin-adenine dinucleotide (FAD) in stoichiometric amounts.

Conclusions:

• WC-1 functions as the primary blue-light photoreceptor in Neurospora crassa.
• This photoreceptor activity of WC-1 is essential for light entrainment of the circadian clock and other light-mediated responses.
• The presence of FAD in the WC-1 complex supports its role as a flavoprotein photoreceptor.