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WHOLE PLANT AND ECOPHYSIOLOGY

Independent Roles for EARLY FLOWERING 3 and ZEITLUPE in the Control of Circadian Timing, Hypocotyl Length, and Flowering Time¹

Department of Plant Cellular and Molecular Biology, Plant Biotechnology Center, Ohio State University, Columbus, Ohio 43210 (W.-Y.K., D.E.S.); and Department of Biology, Kenyon College, Gambier, Ohio 43022 (K.A.H.)

The circadian clock regulates many aspects of plant development, including hypocotyl elongation and photoperiodic induction of flowering. ZEITLUPE (ZTL) is a clock-related F-box protein, and altered ZTL expression causes fluence rate-dependent circadian period effects, and altered hypocotyl elongation and flowering time. EARLY FLOWERING 3 (ELF3) is a novel protein of unknown biochemical function. elf3 mutations cause light-dependent circadian dysfunction, elongated hypocotyls, and early flowering. Although both genes affect similar processes, their relationship is unclear. Here we show that the effects of ZTL and ELF3 on circadian clock function and early photomorphogenesis are additive. The long period of ztl mutations and ELF3 overexpressors are more severe than either alone. Dark-release experiments showing additivity in phase advances suggest that the arrthymicity caused by ZTL overexpression and that of the elf3-1 mutation arise through independent pathways. A similar additive effect on hypocotyl elongation in red and blue light is also observed. In contrast, ELF3 and ZTL overexpressors act similarly to control flowering time in long days through the CONSTANS/FLOWERING LOCUS T (CO/FT) pathway. ZTL overexpression does not delay flowering through changes in GIGANTEA or FLAVIN-BINDING, KELCH REPEAT, F-BOX levels, but through a ZTL-mediated reduction in CO expression. In contrast, ELF3 negatively regulates CO, FT, and GIGANTEA transcript levels, as the expression of all three genes is increased in elf3-1. The elf3-1 co-1 double mutant flowers much earlier in long days than co-1, although FT message levels remain very low. These results show that elf3-1 can derepress late flowering through a CO-independent mechanism. ELF3 may act at more than one juncture, possibly posttranscriptionally.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: David E. Somers (somers.24@osu.edu).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.067173.

^* Corresponding author; e-mail somers.24{at}osu.edu; fax 614–292–5379.

Received June 27, 2005; returned for revision September 13, 2005; accepted September 15, 2005.

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