Ben-Naim, O., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Eshed, R., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Parnis, A., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Teper-Bamnolker, P., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Shalit, A., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Coupland, G., Max Planck Institute for Plant Breeding, D-50829 Cologne, Germany
Samach, A., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Lifschitz, E., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Eshed, R., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Parnis, A., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Teper-Bamnolker, P., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Shalit, A., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
Coupland, G., Max Planck Institute for Plant Breeding, D-50829 Cologne, Germany
Samach, A., Robert H. Smith Institute for Plant Sciences and Genetics, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University, Rehovot 76100, Israel
Lifschitz, E., Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
CONSTANS-Like (COL) proteins are plant-specific nuclear regulators of gene expression but do not contain a known DNA-binding motif. We tested whether a common DNA-binding protein can deliver these proteins to specific cis-acting elements. We screened for proteins that interact with two members of a subgroup of COL proteins. These COL proteins were Tomato COL1 (TCOL1), which does not seem to be involved in the control of flowering time, and the Arabidopsis thaliana CONSTANS (AtCO) protein which mediates photoperiodic induction of flowering. We show that the C-terminal plant-specific CCT (CO, CO-like, TIMING OF CAB EXPRESSION 1) domain of both proteins binds the trimeric CCAATq5 binding factor (CBF) via its HAP5/NF-YC component. Chromatin immunoprecipitation demonstrated that TCOL is recruited to the CCAAT motifs of the yeast CYC1 and HEM1 promoters by HAP5. In Arabidopsis, each of the three CBF components is encoded by several different genes that are highly transcribed. Under warm long days, high levels of expression of a tomato HAP5 (THAP5a) geneq6 can reduce the flowering time of Arabidopsis. A mutation in the CCT domain of TCOL1 disrupts the interaction with THAP5 and the analogous mutation in AtCO impairs its function and delays flowering. CBFs are therefore likely to recruit COL proteins to their DNA target motifs in planta. © 2006 The Authors.
