A quadruple photoreceptor mutant still keeps track of time

Time measurement and light detection are inextricably linked. Cryptochromes , the blue light photoreceptors shared between plants and animals, are crit ical for circadian rhythms in flies and mice [1-3]. WC-1, a putative blue-l ight photoreceptor, is also essential for the maintenance of circadian rhyt hms in Neorospora [4]. In contrast, we report here that in Arabidopsis thal iana the double mutant lacking the cryptochromes cry1 and cry2, and even a quadruple mutant lacking the red/ far-red photoreceptor phytochromes phyA a nd phyB as well as cry1 and cry2, retain robust circadian rhythmicity. inte restingly, the quadruple mutant was nearly blind for developmental response s but perceived a light cue for entraining the circadian clock. These resul ts indicate that cryptochromes and phytochromes are not essential component s of the central oscillator in Arabidopsis and suggest that plants could po ssess specific photosensory mechanisms for temporal orientation, in additio n to cryptochromes and phytochromes, which are used for both spatial and te mporal adaptation.