To ensure that the initiation of flowering occurs at the correct time of year, plants need to integrate a diverse range of external and internal signals. In Arabidopsis, the photoperiodic flowering pathway is controlled by a set of regulators that include CONSTANS (CO). In addition, Arabidopsis plants also have a family of genes with homologies to CO known as CO-LIKE (COL) about which relatively little is known. In this paper, we describe the regulation and interactions of a novel member of the family, COL5. The expression of COL5 is under circadian and diurnal regulation, but COL5 itself does not appear to affect circadian rhythms. COL5, like CO, is regulated by GIGANTEA. Furthermore, COL5 is expressed in the vascular tissue. Using COL5 over-expressing lines we show that, under short days, constitutive expression of COL5 affects flowering time and the expression of the floral integrator genes, FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CO 1. Constitutive expression of COL5 partially suppresses the late flowering phenotype of the co-mutant plants. However, plants with loss of COL5 function do not show altered flowering. Taken together, our results suggest that COL5 has COL activity, but may either not have a role in regulating flowering in wild-type plants or may act redundantly with other flowering regulators.
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Acknowledgments This work was supported by ISF grant 0397386, BSF grant 0378415 and DIP grant 0307712. We would like to thank Alon Samach and David Greenberg (Hebrew University) for their insight and comments on the manuscript, Shai Yerushalmi (Hebrew University) for help with the luciferase imaging system, Maria Belitcky (Hebrew University) for her excellent technical assistance, Lilach Hassidim, Dana Darchy and Marcel Balassiano (Hebrew University) for the photographs, Laurent Courbesier and George Coupland (Max Planck Institute, Cologne) for the CO mutant seeds and David Somers (Ohio State University) for the ZTL mutant seeds.
- CONSTANS-LIKE 5