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DEVELOPMENT AND HORMONE ACTION

A Putative CCAAT-Binding Transcription Factor Is a Regulator of Flowering Timing in Arabidopsis^{1,[C],[W],[OA]}

Department of Plants, Soils, and Climate (X.C., J.B., S.E., E.D., M.L., Y.W.), Center for Integrated BioSystems (D.C.), and Department of Biology (D.D.), Utah State University, Logan, Utah 84322; Syngenta Biotechnology, Inc., Research Triangle Park, North Carolina 27709 (J.K., T.Z.); and Diversa Corporation, San Diego, California 92121 (J.K.)

Flowering at the appropriate time of year is essential for successful reproduction in plants. We found that HAP3b in Arabidopsis (Arabidopsis thaliana), a putative CCAAT-binding transcription factor gene, is involved in controlling flowering time. Overexpression of HAP3b promotes early flowering while hap3b, a null mutant of HAP3b, is delayed in flowering under a long-day photoperiod. Under short-day conditions, however, hap3b did not show a delayed flowering compared to wild type based on the leaf number, suggesting that HAP3b may normally be involved in the photoperiod-regulated flowering pathway. Mutant hap3b plants showed earlier flowering upon gibberellic acid or vernalization treatment, which means that HAP3b is not involved in flowering promoted by gibberellin or vernalization. Further transcript profiling and gene expression analysis suggests that HAP3b can promote flowering by enhancing expression of key flowering time genes such as FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1. Our results provide strong evidence supporting a role of HAP3b in regulating flowering in plants grown under long-day conditions.

² These authors contribute equally to the article.

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: Yajun Wu (yajun.wu{at}usu.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.102079

^* Corresponding author; e-mail yajun.wu{at}usu.edu.

Received May 8, 2007; accepted July 5, 2007; published July 13, 2007.