THE INTERPLAY OF LIGHT AND THE CIRCADIAN CLOCK - INDEPENDENT DUAL REGULATION OF CLOCK-CONTROLLED GENE CCG-2(EAS)

Ambient light is the major agent mediating entrainment of circadian rh ythms and is also a major factor influencing development and morphogen esis. We show that in Neurospora crassa the expression of clock-contro lled gene 2 (ccg-2), a gene under the control of the circadian clock a nd allelic to the developmental gene easy wettable (eas), is regulated by light in wild-type strains. Light elicits a direct and important p hysiological effect on ccg-2(eas) expression as demonstrated using sev eral mutant Neurospora strains. In white collar mutants (wc-1 and wc-2 ) that are 'blind' to blue light, ccg-2(eas) mRNA shows no variation f ollowing illumination with saturating light. By contrast, ccg-2(eas) m RNA is photoinduced in clock-null strains such as frequency9 (bd;frq9) . The results in the clock mutants show that an intact circadian oscil lator is not required for light induction of ccg-2(eas). Thus, ccg-2(e as) is subject to a dual regulation that involves separable regulation by light and circadian rhythm.