ZEITLUPE encodes a novel clock-associated PAS protein from Arabidopsis

We have conducted genetic screens for period length mutants in Arabidopsis using a transgenic bioluminescence phenotype. This screen identified mutati ons at a locus, ZEITLUPE (ZTL), that lengthen the free-running period of cl ock-controlled gene transcription and cell expansion, and alter the timing of the daylength-dependent transition from vegetative to floral development . Map-based cloning of ZTL identified a novel 609 amino acid polypeptide co nsisting of an aminoterminal PAS domain, an F box and six carboxy-terminal kelch repeats. The PAS region is highly similar to the PAS domain of the Ar abidopsis blue-light receptor NPH1, and the Neurospora circadian-associated protein WHITE COLLAR-1 (WC-1). The striking fluence rate-dependent effect of the ztl mutations suggests that ZTL plays a primary role in the photocon trol of circadian period in higher plants.