Project 1:  Analysis of light and circadian-clock regulation of CONSTANS transcription

The CONSTANS (CO) transcriptional regulator promotes flowering of Arabidopsis thaliana in long days characteristic of summer but not in short winter days. The activity of CO is therefore responsible for seasonal control of flowering in Arabidopsis. In response to long days, CO activates transcription of the FT gene, which encodes a small protein that is transmitted from the leaf, where day length is perceived, to the shoot apex, where flowers develop (reviewed by Turck et al (2008) Ann Review of Plant Biology 59, 573).

We recently showed that CO transcription is activated in long days by the action of an F-box ubiquitin ligase, FKF1 (Fornara et al (2009) Developmental Cell 17, 75). The FKF1 protein is specifically stabilized in long days and then promotes the ubiquitination of several DOF transcription factors that repress CO transcription. The stabilization of FKF1 in long days requires GIGANTEA protein, which interacts with FKF1 only in the light and therefore stabilizes it specifically in long days. We showed that in gi mutants, CO is not transcribed because FKF1 is not stabilized and the transcriptional repressors accumulate. However, in complex mutant backgrounds where GI and four genes encoding the transcriptional repressors are inactivated, CO is transcribed almost normally. This result indicates that CO transcription must be activated by an unknown pathway that acts independently of GI and the repressors that we have identified. This project is aimed at identifying components of this pathway through a combination of yeast one hybrid, CO promoter analysis, next generation sequencing of cDNAs and mutant identification.

Project 2: Molecular analysis of juvenility in the perennial species Arabis alpina

The life cycle of annual plants is restricted to a single year, while perennials live for many years and flower repeatedly. We recently described how differential regulation of a MADS box transcription factor between Arabis alpina and Arabidopsis thaliana plays an important part in contributing to perennial or annual life history, respectively (Wang et al (2009) Nature 459, 423). We have also shown how increased and broader expression of the TERMINAL FLOWER 1 (TFL1) gene in Arabis alpina compared to Arabidopsis thaliana represses flowering in the perennial species early in development conferring a juvenile phase to the life cycle. This project will exploit inter-species transfers of key flowering genes to identify changes in gene sequence that confer the differences in gene expression associated with evolution from perennial to annual life history, and examine the functional significance of these differences.